Richard T. Moxley III a, *, Giovanni Meola b,1, Bjarne Udd c,1, Kenneth Ricker d,1. Workshop report

Transcription

1 Neuromuscular Disorders 12 (2002) Workshop report Report of the 84th ENMC Workshop: PROMM (Proximal Myotonic Myopathy) and Other Myotonic Dystrophy-Like Syndromes: 2nd Workshop th October, 2000, Loosdrecht, The Netherlands q Richard T. Moxley III a, *, Giovanni Meola b,1, Bjarne Udd c,1, Kenneth Ricker d,1 a Department of Neurology, University of Rochester, Box 673, 601 Elmwood Avenue, Rochester, NY 14642, USA b Department of Neurology, University of Milan, San Donato Hospital, Via Morandi, 30, San Donato Milanese, Milan, Italy c Department of Neurology, Vasa Central Hospital, Vasa, Finland d Department of Neurology, University of Wurzburg, An der Lehmgrube 9, D Reichenberg, Germany 1. Introduction: Then and now for PROMM Myotonic dystrophy (Steinert s disease) has been known for about 100 years. Its core features are myotonia, muscle weakness, and cataracts. Until recently, clinicians have considered this multisystem disorder to be a single and unique genetic disease entity [1]. It came as a surprise in 1994 that there was another disorder with similar core features [2,3]. However, this disorder seemed to have a sufficient number of different clinical and genetic features in the families studied to justify a separate designation, and the name given to this disorder was proximal myotonic myopathy (PROMM, OMIM *600109). The overall presentation of patients in these families suggested that they might have a clinically and genetically homogenous disease. For that reason, our last ENMC workshop on PROMM in 1997 [4] focused on the clinical and genetic differences between Steinert s disease (myotonic dystrophy; DM-1) and PROMM. The clinical course of PROMM appeared to be more favourable compared with myotonic dystrophy. Families with PROMM did not have the dreaded severe congenital form of illness that occurs in Steinert s disease. Abnormalities in the social and cognitive abilities of adults with PROMM were typically mild or absent in contrast to myotonic dystrophy. In PROMM, there was no prominent q The list of contributors to the workshop giving new data is given in the text in Section 12. * Corresponding author. Tel.: ; fax: address: tracy-forrester@urmc.rochester.edu (R.T. Moxley III). 1 Corresponding reporters for the workshop. weakness of the facial and bulbar muscles. These muscles seemed to have special protection as opposed to Steinert s disease in which deterioration of facial muscle strength, speech and swallowing is typical. In PROMM, manual dexterity remained largely intact, and hypersomnia and mental retardation were not prominent findings. In contrast, these problems are relatively common in Steinert s disease. The genetic basis of PROMM also appeared to be distinct from myotonic dystrophy. PROMM families did not link to the DM-1 locus on chromosome 19q, and unlike patients with Steinert s disease, they had a normal number of CTG repeats in the gene for myotonic dystrophy (DM-1 gene). All of these characteristic features of PROMM have not changed since the 1st ENMC Workshop in October 1997 [4]. They are still valid. However, new observations have occurred since our first workshop. These new observations indicate that certain families with PROMM have affected members with manifestations closely resembling those in myotonic dystrophy. For this reason, this 2nd ENMC Workshop on PROMM has concentrated mainly on the clinical and possible pathogenic similarities between myotonic dystrophy and PROMM. It has also become clear that PROMM is both clinically and genetically heterogeneous [5]. The turning point came in 1998, when Ranum et al. [6] described and mapped a large Minnesota family with myotonic dystrophy-like features to a new locus on chromosome 3q21. They named this locus DM-2. As a result, a new nomenclature has emerged and the gene locus for Steinert s disease/ myotonic dystrophy has received the name DM-1 [7]. Interestingly, it turns out that many families originally diagnosed with PROMM also map to the DM-2 locus. On the other hand, another group of PROMM families do not show /02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S (01)00284-X

2 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) linkage to this locus. One separately described family with marked proximal muscle wasting and weakness, and electrical (findings on electromyography) without clinical myotonia called proximal myotonic dystrophy [8], also mapped to the DM-2 locus [9]. At our first workshop in 1997 [4], we were uncertain whether this family represented a severe example of the PROMM syndrome or if they had another disorder. During this second workshop on PROMM, we have continued to discuss the spectrum of the manifestations of PROMM. In certain PROMM families, there is a wide range of symptoms. Some affected members have the usual, relatively mild, PROMM phenotype, and others have more severe symptoms with involvement of multiple organ systems. Symptoms in the more severely affected individuals often occur in an unpredictable way and are similar to those in Steinert s disease (myotonic dystrophy/dm-1). Some PROMM patients have developed dangerous cardiac problems (conduction block, sudden death, and dilated cardiomyopathy) [10]. Other complications, such as decreased cognitive function [11], have also occurred and may be more common than we indicated in our first workshop report in 1997 [4]. Further investigations are necessary to extend our knowledge of the genotype/phenotype relationships for families who do, and for families who do not, map to the DM- 2 locus. Continued research is also needed to isolate the DM- 2 gene and other new PROMM/DM-related genes (e.g. DM- 3, etc., genes not linked to chromosome 3q21). The goals for this 2nd ENMC Workshop on PROMM were: 1. to review the status of the search for PROMM genes, e.g. gene(s) linked to the DM-2 locus on chromosome 3q21 and those gene(s) not linked to 3q21; 2. to discuss the correlations between phenotype and genotype within different kindreds with PROMM and other DM-like disorders; 3. to consider different possible pathomechanisms that may underlie PROMM and other DM-related disorders; 4. to agree upon certain standardized clinical and laboratory methods to evaluate patients; 5. to review the recently published nomenclature and DNA testing guidelines for DM-1 and other DM-like disorders; 6. to revise our previously recommended diagnostic criteria, supportive findings, laboratory testing and treatment for PROMM [4]. To a large degree, we achieved these goals. Tables 1 3 Table 1 Diagnostic criteria for PROMM and related myotonic dystrophy-like disorders Mandatory inclusion criteria 1) Weakness: neck flexors, hip girdle muscles, and often, the flexor profundus muscles of fingers 2) Myotonia on electromyography (with detailed examination) 3) Cataracts: slit lamp examination demonstrates posterior, subcapsular, iridescent, lens opacities resembling the cataracts typically seen in myotonic dystrophy. Onset of cataracts is before 50 years of age. An exception to this is, if the cataracts have already been removed prior to 50 years of age 4) Autosomal-dominant inheritance: at least two generations; in large kindreds there must be male to male transmission 5) Normal size of CTG repeat in the gene for myotonic dystrophy Supportive findings Muscle and joint pain, fluctuating and episodic Stiffness/myotonia, often very mild or absent clinically Cardiac conduction defects Male hypogonadism: primary type hypogonadism Insulin resistance/glucose intolerance/ diabetes mellitus Compatible findings Calf hypertrophy Painful muscle cramps Intermittent muscle fasciculations Deep tendon reflexes preserved Intermittent episodes of chest pain CNS symptoms: cognitive impairment, hypersomnia, seizures Deafness: sensorineural Hypothyroidism GI symptoms: dysphagia, constipation Frontal baldness Hyperhidrosis Provocative conditions: pregnancy, hypothyroidism, hypoparathyroidism Unlikely findings Ophthalmoplegia Predominant distal wasting at onset

3 308 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) Table 2 Tests and findings supporting the diagnosis of PROMM and related myotonic dystrophy-like disorders Muscle biopsy findings Increased numbers of central nuclei; variation in fibre size; pyknotic clumps; scattered angular fibres; occasional ring fibres; type I fibre predominance; no preferential type I fibre atrophy The biopsy helps to exclude some other myopathic disorders Mitochondrial disorders Progressive dystrophinopathic muscular dystrophies Autosomal recessive limb girdle muscular dystrophies (antibody screening for different membrane associated proteins) Inclusion body myositis Glycogen storage disease, e.g. acid maltase deficiency Laboratory tests Creatine kinase: mildly elevated or normal Liver function: gamma glutamyl transferase mildly elevated or normal Electrocardiogram: increased frequency of cardiac conduction abnormality Thyroid function: normal TSH and T4 Glucose tolerance testing: may demonstrate increased insulin release following oral and intravenous glucose loading (findings typical for insulin resistance), and may show impaired glucose tolerance or occasionally diabetes mellitus Gonadal function testing: may demonstrate increased FSH, increased LH, and decreased testosterone levels in males Electromyography Electrical myotonia; normal or borderline slowing of nerve conduction; normal repetitive stimulation a Imaging of brain Occasional white matter changes appear on magnetic resonance imaging of brain, but MR is often normal PET shows abnormalities in frontal lobes in some patients a Comment: motor unit morphology may have myopathic or neuropathic features in different patients, and some patients have normal morphology of the motor unit potentials. summarize our revised recommendations for the diagnostic criteria for PROMM, the tests and findings supporting the diagnosis, and the treatment guidelines. Below are highlights of the workshop. 2. Advances in the molecular genetics of PROMM and other DM-like syndromes Over the past 2 1 / 2 years since the 1st ENMC Workshop Table 3 Treatment guidelines for PROMM and related myotonic dystrophy-like disorders Myotonia Often no treatment required. Phenytoin or mexiletine may be helpful. Serial monitoring of electrocardiogram is necessary during treatment with mexiletine Cataracts Surgical removal often becomes necessary Cardiac problems Serial monitoring of electrocardiogram is recommended to detect covert arrhythmia Pacemaker treatment may be necessary. Sudden death is a concern and detailed cardiac evaluation is necessary in families having such a history Muscle pain Occasionally, treatment with non-steroidal anti-inflammatory drugs or carbamazepine, or a short-term course of corticosteroid therapy may ameliorate this peculiar muscle pain. Severe attacks of pain have required intravenous opiates and benzodiazepines. Some patients have improved after Mexiletine. However, no consistently effective preventive treatment is known, and no controlled trials of treatment for this problem have occurred. Low dose tricyclic-antidepressant therapy may be an option to consider. Increased understanding of the origin of this pain is necessary Advice related to surgical procedures Patients need to be aware of the potentially increased risk of general anaesthesia as outlined below Referral of a PROMM patient for hip replacement surgery requires special consideration. Referred pain from the hip joint goes to the thigh, but the peculiar muscle pain in PROMM can sometimes mimic this referred pain from the hip Anaesthesia risk Avoid depolarizing muscle relaxants. Avoid abnormal elevation of serum potassium during anaesthesia. Target a concentration of 4 meq/l. Monitor postoperatively for rhabdomyolysis and renal failure, especially in patients having elevated levels of creatine kinase

4 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) on PROMM, we have learned about an intriguing genetic homogeneity in some kindreds with PROMM and related DM-like disorders. We have also learned, not surprisingly, that there is genetic heterogeneity in some families that have the typical characteristics of PROMM described in the report of our first workshop [4]. A major advance in our understanding of the gene defect(s) responsible for PROMM came in Dr Laura Ranum and colleagues described a large Minnesota kindred in whom many affected individuals had clinical signs and symptoms resembling myotonic dystrophy. These same patients had a normal size of the CTG repeat in the DM-1 gene. Dr Ranum and her co-workers named this disorder myotonic dystrophy type-2 (DM-2) and demonstrated linkage to chromosome 3q21 [6]. A companion report in 1999 by Dr John Day and colleagues, involving that same Minnesota family, described the different clinical manifestations. As a part of that report, Dr Day described certain affected individuals who had findings indistinguishable from previous descriptions of PROMM [12]. The clinical similarities between certain members of this Minnesota DM-2 family and patients with PROMM led Dr Kenneth Ricker and coworkers to perform linkage analysis in nine German families with PROMM to see if any of these families mapped to the DM-2 locus. Dr Ricker and co-workers found linkage in eight of these nine families to chromosome 3q21 [13]. These observations strongly suggested that many patients with PROMM have DM-2 or an allelic genetic disorder [14]. Recent studies have established linkage of the Finnish family previously described with proximal myotonic dystrophy by Dr Udd and co-workers [8] to the DM-2 locus [9]. This family has severe muscle wasting and weakness. Such severe clinical manifestations were originally thought to be inconsistent with the diagnosis of PROMM, since these findings differed with the milder phenotype described originally. This assumption now seems incorrect, at least for certain families that link to the DM-2 locus. It will be a challenge to identify the switch, the molecular pathomechanism, that permits potentially similar mutations at the 3q21 locus to cause severe wasting and weakness in some families, and, in other families, to cause only minimal weakness without wasting, as occurs in typical PROMM. It will also be a challenge to identify the common pathomechanisms that underlie the variable manifestations of the different PROMM syndromes and to use that information to clarify how mutations in different genes can lead to similar clinical findings. Not all families with the typical PROMM phenotype, as described in the 1st ENMC Workshop on PROMM in 1997, map to the chromosome 3q21 locus. Reports in 1999 [9,15] and 2000 [16] describe PROMM families that do not link to the DM-2 locus. It is clear now that PROMM is a syndrome that results from different mutations. However, despite this genetic heterogeneity, there appear to be common pathophysiological alterations shared by the different genetic forms of PROMM, and certain of these pathophysiological alterations also occur in myotonic dystrophy/dm-1. During this second workshop, Dr Laura Ranum and colleagues summarized the progress that they have made toward identifying the gene(s) at chromosome 3q21 responsible for DM-2/PROMM. Dr Ranum and her colleagues have performed clinical and genetic evaluations in 18 Minnesota families and 19 German families with linkage to chromosome 3q21. Affected individuals in these families have varied in their degree of muscle weakness and in its distribution, but all have displayed myotonia on electromyography. To obtain LOD scores and to focus the search for the gene, Dr Ranum has developed a genetic model and a series of liability classes for patients. They have made two fundamental assumptions about affected individuals in their model: (a), myotonia (on electromyography) becomes detectable by years of age; and (b), the phenocopy number is low in the general population, e.g. 1:1000. Dr Ranum and colleagues have narrowed the region containing the DM-2 locus from 3.0 to approximately 0.5 cm. Isolation of the gene appears to be close at hand. In addition to the progress being made by Dr Ranum and co-workers, Dr Ralf Krahe and colleagues also presented promising results of work in his laboratory. Dr Krahe has 46 PROMM families available for genetic studies, 11 of which link to chromosome 3q21. One of these families is the family originally described by Udd et al. with proximal myotonic dystrophy [8]. Dr Krahe and co-workers have used a genome-wide scan to search for the DM-3 locus in 3q21 non-linked families. They have used 400 markers to search at 10 cm intervals. Logarithm of the odds (LOD) scores are encouraging for two loci. Dr Krahe also mentioned that his group has genetic analyses in progress on DM-2 linked families for isolation of the gene and mutation(s). It is likely that within the next year, researchers will isolate the DM-2 and DM-3 (or more) genes. The following two sections of this report describe the clinical and laboratory characteristics of two categories of PROMM families: (a), those with established linkage to the DM-2 locus; and (b), those without linkage to chromosome 3q Clinical and laboratory findings in PROMM families with linkage to chromosome 3q21/DM-2 locus Dr Kenneth Ricker presented extensive new information describing 82 living patients from 15 PROMM families linked to the DM-2 locus. Table 4 summarizes this information. Dr Ricker also described three different clinical presentations of PROMM that he has observed. The first presentation was that of a patient having the typical, relatively mild, clinical course described for PROMM in the 1st ENMC Workshop [4]. The second was also a typical PROMM patient. However, sudden death occurred from a disturbance in cardiac conduction. The third presentation was of a patient who had a later onset of PROMM and who

5 310 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) Table 4 Summary of core complaints a and findings in 82 PROMM patients b from 15 German families that map to the DM-2 locus on chromosome 3q21 c Percentage of patients Age (years; n ¼ 82) at first core symptom Age of appearance of first core symptom based upon recollection of the patients Myotonia Weakness Cataract Clinical and laboratory features in the 82 PROMM patients linked to chromosome 3Q21 Electromyographic myotonia 97 Weakness 76 Elevation of creatine kinase d 73 Elevation of gamma glutamyl transferase d 70 Clinical myotonia 66 Cataract 47 Muscle pain 46 Tremor 28 Electrocardiographic abnormalities 21 Hypogonadism 18 a b c d Myotonia, weakness, cataracts. Thirty-four men; 38 women. These data were obtained by Dr Kenneth Ricker and colleagues. These elevations were episodic, not constantly present. unexpectedly developed a rapid deterioration in muscle function. This third patient complained of myotonia in his 40 s and muscle weakness in his 50 s. Three years after the onset of weakness, he progressed rapidly to severe quadriparesis. No obvious signs of stroke, no evidence of neuromuscular transmission disease, and no signs of polyneuropathy were apparent. Dr Ricker has seen three such rapidly progressive cases. Such patients have severe weakness of the neck, as well as proximal and distal weakness. Muscle biopsies and detailed imaging of the brain have not been performed in these three cases. Further evaluation is necessary to establish that the cause(s) for the rapid loss of muscle strength in these cases is a manifestation of PROMM. We presume that PROMM was the major factor. The cases of sudden death and of progressive severe weakness emphasize that PROMM is not necessarily a benign syndrome. There are more similarities to myotonic dystrophy than the initial reports have suggested [10]. The genetic and other factors that trigger these serious complications in certain PROMM patients are unknown and need investigation. Dr John Day presented clinical information about the large Minnesota family (MN-1) that he and others originally described with myotonic dystrophy type-2/dm-2 [12]. Dr Day also presented the findings from 18 additional families with linkage to the DM-2 locus, giving a total of 71 affected individuals. Most patients were of German ancestry. Their initial diagnoses varied and included myotonic dystrophy (82%), polymyositis (9%) and mitochondrial myopathy (9%). Dr Day emphasized that cataracts typical for Steinert s disease and myotonia on electromyography were highly penetrant features in all of their cases of PROMM/ DM-2 linked to chromosome 3q21. A high percentage of the patients had selective weakness of the long flexors of the fingers: (a), thumb (39/46); (b), index (43/46); and (c), long finger (28/45). There was less weakness in the flexors of the fourth (17/45) and fifth fingers (16/45). Weakness of neck flexors (34/55) was more common than muscles of eye closure (7/55). Most patients had difficulty performing a deep knee bend, and approximately one-third had weakness of shoulder abduction. Dr Day indicated that preliminary studies of the effects of warming of the limbs prior to electromyography failed to provoke an increase of myotonia as others had reported previously [17]. More investigation of the effects of warming on myotonia in PROMM/DM-2 is necessary to establish its usefulness in unmasking or amplifying myotonia in this disorder. A high percentage of the patients in the original MN-1 family [12] reported excessive sweating. Dr Day noted, however, that in the other PROMM/DM-2 families, he evaluated that hyperhidrosis is a less prominent complaint. The significance of hyperhidrosis as a supportive feature in the diagnosis of PROMM/ DM-2 needs further clarification. Elevations of creatine kinase, facioscapulohumeral muscular dystrophy (FSH), and serum insulin were frequent in the PROMM/DM-2 patients described by Dr Day. The consensus of those attending this 2nd Workshop on PROMM was that the PROMM families linked to chromosome 3q21 and Minnesota families with myotonic dystrophy type-2/dm-2 have the same disorder, PROMM/DM-2. Dr Moxley and Dr Thornton gave an update on two large DM-2 linked families from the Rochester, NY area that they had described at the 1st Workshop on PROMM in They indicated that central nervous system (CNS) manifestations have become more prominent in affected

6 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) individuals. Three had developed cognitive deficiency since 1997: one man of 28 years of age; two women, one 42 and one 62 years of age. All had typical cataracts, mild clinical and electromyographic myotonia, and mild weakness of neck flexors and proximal leg muscles. All had normal strength of the long finger flexors. The father of the 28-year-old man had to take early retirement because of problems with his memory. He began to have cognitive disturbance in his 40 s, shortly after he first noticed grip myotonia. The father of the 42-year-old woman had developed the core features of PROMM in his 50 s, and in his 60 s had developed a movement disorder diagnosed as atypical Parkinson disease. Magnetic resonance (MR) of the brain in the three patients and in the two fathers revealed no masses, malformations, or demyelinating lesions. A search for abnormal laboratory values to account for the cognitive loss in these patients was negative. PROMM appears to be the cause. Dr Moxley and Dr Thornton also described the accidental discovery of three new patients with PROMM referred for electromyography by their primary care physicians to rule out radiculopathy. These observations suggest that we are underestimating the true prevalence of PROMM. A number of undiagnosed patients seem to have subclinical myotonia, and they attribute their symptoms, such as, stiffness, aches, and pains, to muscle overuse, root disease, arthritis, or simply to old age. Dr Meola presented three large Italian PROMM families linked to chromosome 3q21, including an interesting family with prominent seborrheic keratoses [18]. Affected members of this family had moderate proximal leg weakness, mild shoulder girdle weakness, cataracts, and hypogonadism, but they did not have weakness of the face, neck flexors, or finger flexors. They had no cardiac conduction disturbance. No characteristic clinical features were apparent to distinguish the PROMM patients with keratoses from PROMM families not having these skin lesions. Further study of the relationship between the presence of these keratoses and the pathomechanism of PROMM is needed. Dr Bassez has evaluated 23 patients with PROMM [19]. The patients are from 14 unrelated families (nine from France, three from Poland, one from Spain, one from North Africa, and six sporadic cases). He presented the findings from the first 13 of these patients. Initial symptoms were: (a), weakness (10/13); (b), muscle pain (2/13); and (c), unexplained elevation of serum creatine kinase (1/13). The location of the first weakness that the patients recalled was either in the hip girdle (11/13) or neck flexors (2/13). At the time of examination, all 13 had proximal weakness and 12/13 had distal weakness. Approximately half of the patients had muscle pain. Only 1/13 had clinical myotonia, while all had myotonia on electromyography. Cataracts occurred in 11/13. Abnormalities in cardiac conduction were relatively common in these 13 patients. Prolonged intraventricular conduction was present in 10/13, and clinical symptoms of cardiac disease occurred in 5/13. One died of sudden death, and one had atrial fibrillation. In one family, a mother with typical mild clinical features of PROMM had a son who had mental retardation diagnosed at the age of 3 years, and who now, at the age of 21 years, has myotonia on electromyography. This observation prompted a discussion of a possible congenital form of PROMM, and the similarity to the triplet repeat disease, DM-1, myotonic dystrophy. Dr Schneider indicated that she has two patients with mental retardation diagnosed early in childhood who also have developed findings of PROMM. However, there was agreement that more information is necessary to establish the existence of a congenital form of PROMM, and to clarify the possible role repeat expansion as the basis of PROMM. Dr Schneider summarized clinical information on 27 parent child pairs from ten families linked to chromosome 3q21. Her findings support the existence of anticipation in the PROMM families linked to the DM-2 locus [20]. Symptoms began, on average, 1.8 decades earlier in the child compared with the parent. This observation is consistent with the possibility that there may be a congenital form of PROMM. It also supports the hypothesis that PROMM linked to the DM-2 locus may result from an unstable expansion of DNA. Dr Johnson pointed out that there are certain trinucleotide repeat diseases, such as spinocerebellar ataxia type 7, that lack congenital cases. However, Dr Harper emphasized that an absence of clearly documented congenital cases indicates that PROMM does differ in a fundamental way from myotonic dystrophy, DM-1. Dr Schneider has examined a total of 100 families with PROMM, and the total number of parent child pairs is 63 from 38 families. As specific gene probes become available, it will be possible for her to extend her study of anticipation in PROMM families linked to DM-2 and to search for evidence of anticipation in those PROMM families not linked to chromosome 3q21. These future investigations will help to determine if similar genetic mechanisms are associated with the similar clinical manifestations that occur in linked and non-linked kindreds. Dr Rogers provided additional data on a large DM-2 linked PROMM family, to supplement their previously published data [21]. He emphasized that the muscle biopsy samples obtained in selected patients from this family showed an increased number of fibres with central nuclei and an increased number of small angular fibres. These alterations are the same as those described by others and are the same as those described for PROMM in the 1st Workshop on PROMM [4]. Dr Udd reviewed data on Finnish families with DM-2 linked PROMM/PDM (proximal myotonic dystrophy) and focused primarily on the muscle biopsy findings. The muscle specimens from moderately weak muscles show an increase in central nuclei, nuclear clumps, scattered highly atrophic fibres, only occasionally necrotic fibres, and fibres with rimmed vacuoles. In the later stage of the

7 312 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) disease in the proximal myotonic dystrophy family, there was fibrosis and fatty accumulation more in a perifascicular location and less in the endomysium. Most of the small fibres were type 2, detected in larger numbers by immunohistochemistry than by ATPase reaction. Dr Udd encouraged further studies of muscle biopsy specimens and reemphasized the suggestion of Dr Thornton given at the first workshop [4] that we develop a protocol for different laboratories to use in the examination of muscle tissue from patients with PROMM. Whether the findings on muscle biopsy in the Finnish patients with PROMM represent the severe end of the spectrum of pathological changes in muscle that result from mutations at the DM-2 locus requires clarification. It is possible that some of these findings represent an additional pathological process associated with some unique feature of the specific mutation in chromosome 3q21 that causes PROMM. 4. Clinical and laboratory findings in PROMM families without linkage to chromosome 3q21/DM-2 locus Dr Schulte-Mattler presented clinical data on a large East German family with PROMM not linked to the DM-2 locus [16]. Of the ten family members examined, five patients had myotonia, and three of these had cataracts. Another had typical cataracts for PROMM, but had no myotonia on electromyography and no weakness. Three of the five patients with myotonia had weakness of neck flexors and proximal hip/ thigh muscles. This weakness developed in their 40 s and 50 s. Muscle biopsy revealed an increased number of central nuclei and an increased variation of fibre diameter. The findings in this PROMM family are indistinguishable from those in most of the unlinked families. Dr Schulte-Mattler also mentioned that his group has evaluated 21 more PROMM patients from 14 unrelated families, but the families are too small to permit linkage studies. Interestingly, 17 are female and only four are male. Initial symptoms occurred between 20 and 58 years of age with 63% having weakness, 50% having muscle pain, and 37% having muscle stiffness. All had myotonia on electromyography. Three patients developed weakness, muscle pain, and myotonia during pregnancy. These symptoms disappeared quickly after delivery. Two patients had clinical signs of CNS dysfunction accompanied by normal MR studies of the brain. Another three patients had confluent white matter alterations on MR of the brain, but no clinical symptoms of CNS disease. Dr Ricker described 12 patients from three different PROMM families not linked to the DM-2 locus. Six were male and six were female, and they ranged in age of onset of their first symptoms from 21 to 52 years of age. Five presented with myotonia, five with weakness, and one with cataracts as their first symptom. Three of the 12 had all three core symptoms, e.g. myotonia, weakness, and cataracts. They ranged in age from 47 to 66 years. Five of 12 had two core symptoms and ranged in age from 42 to 68 years. Three of 12 had one core feature and ranged in age from 24 to 45 years. There was a gender effect on strength. The men appeared to have less weakness, while women had a similar degree of weakness compared with individuals from PROMM families linked to the DM-2 locus. The degree of clinical myotonia was very mild and required electromyography for definite identification. Dr Meola presented clinical and laboratory data on a fivegeneration family from Northern Italy that was not linked to the DM-2 locus to supplement their previously published data [22]. There are 11 definitely affected individuals who have had symptoms for an average of 17.5 ^ 10 years (mean ^ SD). Of the seven family members examined, only two had clinical myotonia and four had cataracts. The age of onset ranged from the 2nd to 4th decades. Three of seven had weakness of the legs as their initial symptom, two had myalgia and two had myotonia. Three of the seven complained of muscle cramps. Two had hand tremor. No patient had frontal balding or hyperhidrosis. One had loss of hearing. On follow-up examination 6 years later, all patients showed progression of proximal weakness in their shoulders (grade 3 1 /5; MRC grade). Most were unable to arise from a squat and they needed to hold the railing to climbs stairs. However, none of the patients reported major limitations at work or at home. Tendon reflexes were preserved in all patients at their initial examination and were unchanged or increased on follow-up examination 6 years later. Muscle biopsies were performed in two patients. There was an increase in the number of central nuclei, an increased variation of fibre diameter and no atrophy of type I fibres. Electrocardiograms on initial evaluation and at follow-up showed no cardiac arrhythmias. Computed tomography (CT)/MR imaging of the brain showed no significant alterations. Dr Lipsi presented a kindred with PROMM not linked to the DM-2 locus in which two unrelated individuals married and both had myotonia. The female had a history of dominantly inherited myotonia in her family, but there was no history of cataracts. The male also had myotonia without a clearly defined family history. All three of their children had early onset of symptoms, with myotonia beginning in early childhood and proximal weakness occurring between 13 and 19 years of age. One developed cataracts at the age of 17 years. Another had cardiac arrhythmia by the age of 28 years. Linkage studies have not been performed in the mother s family to determine if there is linkage on her side of the family to a mutation in either the skeletal muscle sodium or chloride channels. The early onset of symptoms in this kindred raises the possibility of gene interaction, such that mutations in the sodium or chloride channel may exert an accelerating effect on the clinical manifestations in PROMM. Later in the workshop, Dr Jurkat-Rott spoke about a similar inducing or amplifying effect caused by a mutation in the chloride channel occurring in combination with PROMM.

8 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) PROMM families with undetermined linkage Dr Keith Johnson briefly described several families in which linkage to 3q21 is equivocal. Two of these families had affected individuals with weakness and myotonia closely resembling the weakness and myotonia in myotonic dystrophy, DM-1, but none of the affected individuals had cataracts. How these families fit into the clinical spectrum of PROMM requires further study. Dr Lipsi reviewed clinical data on several Italian PROMM families without established linkage to the DM-2 locus. In one family, an affected individual had severe dysphagia, mental retardation, weakness, and was unable to ambulate at the age of 30 years. In another kindred, there was an earlier age of onset of symptoms in three successive generations, suggesting possible anticipation in that PROMM kindred. Dr Meola described another Italian family without established linkage to the DM-2 locus. There were seven affected individuals, five women and two men. Proximal weakness was severe and resembled that observed in proximal myotonic dystrophy described by Udd and colleagues [8]. The patients also had elevated levels of cholesterol, as did the patients reported by Udd. However, these patients had prominent grip and percussion myotonia unlike the patients described by Dr Udd. To complete this section of the workshop, Dr Udd described a new PROMM kindred with four generations that had originally been diagnosed as having myotonic dystrophy before DNA testing. All affected individuals had a normal size of the CTG repeat in the DM gene. At present, there is no established linkage in this kindred to the DM-2 locus. One interesting finding that appears on analysis of the family tree is the appearance of anticipation. Affected individuals in the second generation have all had an earlier onset of symptoms. The initial symptom in the affected individuals was proximal leg weakness, and eventually, all developed marked difficulty in arising from a chair or climbing stairs. Calf hypertrophy occurred commonly in the second generation. Affected individuals in this generation developed symptoms earlier in life. Later in the course of the disease, most affected individuals develop significant weakness of ankle stabilizers. They walk with their knees flexed to help maintain their balance. This way of walking is very similar to that of patients with classical myotonic dystrophy. Cataracts, tremor, and cardiac conduction disturbances have also occurred in the affected individuals in this kindred over time, as has male hypogonadism. The symptoms and findings in this family and in the other families without established linkage to the DM-2 locus described above by Drs Johnson, Lipsi, and Meola are similar to those observed in the families definitely linked or not linked to the 3q21/DM-2 locus. This similarity provides a strong clinical argument that the different underlying genetic defects have a common underlying pathophysiological alteration. Once the DM-2 and DM-3 (and additional loci) genes are known, we anticipate that these putative shared pathophysiological alterations will be easier to identify. In the meantime, we may be able to obtain clues from some of the unusual manifestations that occur in PROMM. 6. Unusual phenotypes in families with PROMM To start this portion of the workshop, Dr Ricker presented selected examples of peculiar borderline cases from families with PROMM to emphasize the wide variability that occurs in this syndrome. He described a small family in which one affected individual had the phenotype typically associated with a motor neuropathy. In another family, the grandmother first manifested signs of PROMM at 70 years of age and developed a rapidly progressive asymmetric weakness resembling atypical motor neuron disease. The mother developed myalgias at 41 years of age, cataracts and proximal leg weakness in her mid 40 s, and myotonia at 47 years of age. Her symptoms followed the more typical course originally described for PROMM. The patient, who was 21 years of age, developed her first signs of PROMM during pregnancy. This family emphasizes not only the unusual asymmetric rapid weakness that can occur with the late onset of PROMM, but also demonstrates an example of the earlier onset of symptoms in successive generations very suggestive of anticipation. Dr Ricker also mentioned that at present, there are approximately 180 PROMM families in Germany. He and his colleagues have investigated 120 of these families. Twenty-three of these families have more than three living affected individuals. Out of this large group of families, 15 definitely map to the 3q21/DM-2 locus, while three families have been definitely excluded from the DM-2 locus. The majority of these German families require future gene testing to establish which genetic form of PROMM has affected their members once the PROMM and other DM-related disease genes have been isolated [14,23]. Other participants in the workshop described unusual phenotypes of PROMM. Dr Bassez described a family of five generations in which certain affected individuals had early onset of dementia. Dr Meola reported a case of a PROMM patient who initially had delayed motor milestones as a child, developed depression at 28 years of age, and psychosis at 29 years of age. At the age of 40, he developed diabetes, at the age of 50, muscle cramping, and at the age of 60, proximal muscle weakness. Electromyography revealed myotonia, creatine kinase was elevated three-fold, and MR imaging of the brain showed cortical atrophy with normal appearance of the white matter. Dr Meola asked whether all of the symptoms in this patient directly relate to PROMM or whether they represent separate disorders that caused retardation of motor development, psychosis, diabetes, and PROMM. It may be that this patient has an unusual phenotype of PROMM. Dr Udd presented a family in which there was a 54-year-

9 314 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) old PROMM patient who had congenital hypotonia. This patient only walked after 2 years of age. He stopped walking at 16 years and was noted to have mild mental retardation. He developed clinical signs of myotonia at 27 and generalized muscle atrophy at 44 years of age. On laboratory testing, he had evidence of hypogonadism and cerebellar hypoplasia. He had a muscle biopsy at 54 years of age. It showed prominent central nuclei and increased fibrosis. His sister died when she was 30 years of age. At that time, she had cataracts and mental retardation. There was no autopsy. His parents are still alive and well into their 70 s. Does this patient have an unusual form of PROMM? Does this family represent autosomal recessive form of the PROMM syndrome? Answers to these questions await the isolation of the genes responsible for PROMM and other DM-like disorders and the precise determination of the natural history of these different PROMM syndromes. 7. Assessment standards for evaluation of patients As the different gene mutations are identified that lead to the PROMM phenotype and the other DM-like disorders, it will become increasingly important to establish reliable, practical, clinical and laboratory methods to assess the various manifestations of these disorders. Ideally, these methods of assessment will provide a means to define the natural history for each of the multisystem manifestations that occur in PROMM and the other DM-like disorders. Symptoms and findings related to muscle weakness and myotonia need to be quantitated. However, in many patients, involvement of other organs, such as the heart, the brain, the eyes, and the endocrine system, lead to clinical problems of greater concern than the symptoms due to the alterations in skeletal muscle function. In an earlier session of the workshop, Drs Meola, Ricker, Bassez, Udd, Thornton, and Moxley gave examples of PROMM patients afflicted with disabling symptoms caused by either altered function of the heart or the brain. Dr Meola, in this section of the workshop, reviewed the new findings concerning the heart and the brain in patients with PROMM Heart Defects in cardiac conduction are well known in myotonic dystrophy/dm-1. However, at present, there is a limited amount of information published describing serious cardiac problems (conduction block, sudden death, dilated cardiomyopathy) in PROMM [10]. The anecdotal reports given in this workshop that indicate serious cardiac problems in several PROMM families represent the largest number of cases of cardiac dysrhythmias described thus far. More detailed publications of the prevalence and the natural history of cardiac alterations in PROMM are necessary. We recommend the establishment of a core of routine measurements of cardiac function (ECG, 24 h Holter, ECHO) which will be part of the routine, initial work-up of PROMM patients, especially those with a family history of cardiac conduction disturbance or sudden death. It still appears that the majority of patients with PROMM do not have serious disturbances of cardiac conduction. Dr Meola and colleagues have described a large Italian PROMM family that was not linked to the DM-2 locus in which none of the affected members had arrhythmias, angina, pectoris, or shortness of breath after exercise. Twenty-four hour Holter monitoring at their initial and follow-up examinations did not detect any abnormality in cardiac conduction [18]. This contrasts with the natural history typical for myotonic dystrophy, DM-1. Patients with DM-1 often have disturbances in cardiac conduction, which increase in frequency, as they grow older. The exact frequency of cardiac abnormalities in PROMM, whether linked or not linked to the DM-2 locus, remains to be established. Further investigations are necessary to extend our knowledge of the genotype/phenotype for cardiac involvement Brain The workshop recommends establishing appropriate methods for evaluating brain function, as well as structure, in PROMM. Recent reports demonstrate that alterations of brain structure and function occur in PROMM [5,11,24]. The first reports of CNS involvement came when Hund and colleagues described six patients with PROMM [24] who had no clinical signs of brain dysfunction, but had many confluent white matter lesions on MRI of the brain. These alterations in the white matter were similar to those described in cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Based upon present reports, the majority of PROMM patients with CNS problems do not have extensive alterations in the white matter [22]. Many patients have no diagnostic abnormalities on MR of the brain but have alterations of brain function. Dr Meola and colleagues performed a battery of neuropsychological tests on patients with PROMM and compared them with patients with myotonic dystrophy, DM-1. There were significant impairments in visual spatial function in both groups. Patients with PROMM had similar but less severe alterations in neuropsychological function compared with those in patients with DM-1. Since the neuropsychological defects could not be explained by abnormalities of brain structure, these patients underwent positron emission tomography (PET) studies of the brain. Both PROMM and DM-1 patients had a reduction in cerebral blood flow (CBF) in the frontal and temporal lobes [11]. The PROMM patients in these studies came from families without linkage to the DM-2 locus. It is possible that the cognitive dysfunction associated with reduced CBF observed in this subset of PROMM patients may not occur in PROMM patients with linkage to the 3q21/DM-2/ PROMM locus. Further investigations are necessary to confirm and extend these findings.

10 R.T. Moxley III et al. / Neuromuscular Disorders 12 (2002) Skeletal muscle: weakness, wasting, and myotonia The 1st PROMM Workshop Report and subsequently published reports have emphasized that both the weakness and myotonia in PROMM often vary in severity, sometimes from day to day, sometimes from week to week, sometimes at longer intervals [25]. In order to define more precisely the natural history of the myotonia and weakness in PROMM (both linked and without linkage to the DM-2/3q21 locus) and in the other DM-like disorders, the members of the 84 th ENMC Workshop have recommended that we identify reliable methods to measure muscle strength, muscle mass, and myotonia. Dr Moxley presented examples of questionnaire instruments to assess muscle function and muscle pain. He also distributed handout materials that described and critiqued various clinical and laboratory methods that can be used to evaluate strength, muscle mass, myotonia, hormonal disturbances (insulin resistance; thyroid dysfunction), electrodiagnostic findings, muscle biopsy morphological results, and the findings observed on different imaging studies. These materials constitute the basis for ongoing work by the PROMM workshop participants to develop specific recommendations for the most appropriate methods to define the natural history of the different clinical and laboratory manifestations of PROMM. We anticipate that certain of these methods will prove useful in determining the efficacy of various treatments in future therapeutic trials. The specific information contained in the handout materials is too detailed to include in this summary of the workshop. In the future, another PROMM workshop will devote a major portion of time to developing specific methods to assess disease manifestations and these methods will be described in detail in that workshop report. 8. Pathomechanism, modifying genes, and animal models 8.1. Pathomechanism Dr Ashizawa discussed the three different mechanisms considered to be the basis for the multisystem manifestations in myotonic dystrophy, DM-1, and raised the possibility that some portion of these mechanisms may contribute to the manifestations in PROMM. In myotonic dystrophy, the three proposed genetic pathomechanisms are: (a), an abnormal expression of the DM protein kinase (may contribute to cardiac symptoms); (b), an altered expression of the flanking genes Six5 (3 0 end of DMPK gene may contribute to cataracts) and DMWD (5 0 end of DMPK gene may contribute to testicular and brain manifestations); and (c), a toxic gain of function due to the accumulation of CUG mrna transcripts in the myonuclei (cause alterations in processing/splicing, binding of transcription factors may contribute to the myotonia and myopathy). The clinical phenomenon of anticipation is present not only in DM-1, but also in PROMM/DM-2 linked to 3q21 [6,12,20]. This raises the possibility that the DM-2 form of PROMM may result from some type of unstable nucleotide repeat and have a pathomechanism that is similar to myotonic dystrophy, DM- 1. Discovery of the DM-2 gene will help to clarify this possibility Modifying genes Dr Jurkat-Rott presented data on the possible interactive effects of the human skeletal muscle chloride channel mutation, R894X, on PROMM, myotonic dystrophy, and other myotonic disorders. Patients with PROMM and myotonic dystrophy not uncommonly have elevated levels of gamma glutamyl transferase (GGT) in the blood. Based upon their initial observations in PROMM patients, who also have the R894X mutation in the chloride channel, Dr Jurkat-Rott and colleagues reached three tentative conclusions. They suspect that the R894X mutation accentuates myotonia, increases the elevation of GGT, and contributes to the episodic nature of symptoms in PROMM. Dr Peter Harper recommended that sib pair studies and other approaches will prove useful in establishing more conclusively if the R894X mutation is acting as a modifier gene in PROMM and related disorders [26] Animal model Dr Charles Thornton discussed the results of studies performed in his laboratory using a transgenic mouse model of myotonic dystrophy that he and his colleagues have developed [27]. Dr Thornton and co-workers have produced a transgene using the human skeletal muscle actin gene containing either long CTG repeats (250 repeats) or short CTG repeats (five repeats). In mice overexpressing the long repeat, there is an accumulation of CUG repeats in the myonuclei. Within 6 weeks, the mice develop myotonia, and several weeks later, they develop muscle weakness. The mice appear to have developed the myotonia and myopathy as a direct result of the toxic accumulation of the long repeat mrna transcripts. This pathophysiological effect of the CTG repeat expansion in the transgene has occurred without any influence on the DM protein kinase gene or any local structural effect on homologues of Six5 or DMWD genes. These findings raise the possibility that the toxic accumulation of certain types of repeat expansions in the myonuclei may cause symptoms independent of a direct effect on the gene containing such a mutation. It may be that the similar clinical manifestations that occur in PROMM and myotonic dystrophy result from repeat expansions that are similar in their pathological effect despite being associated with different genes on different chromosomes. The eminent discovery of the different gene defects that cause the PROMM syndrome will move us closer toward confirming this speculation.