Duchenne muscular dystrophy quantification of muscular parameters and prednisone therapy Beenakker, Ernesto Alexander Christiaan

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1 University of Groningen Duchenne muscular dystrophy quantification of muscular parameters and prednisone therapy Beenakker, Ernesto Alexander Christiaan IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2005 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Beenakker, E. A. C. (2005). Duchenne muscular dystrophy quantification of muscular parameters and prednisone therapy s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date:

2 CHAPTER 1 General Introduction.

3 Duchenne muscular dystrophy (DMD) is an X-linked recessive neuromuscular disorder clinically characterised by progressive muscle weakness starting in childhood and leading to death around the age of 20 years. 1 With an estimated birth prevalence of 1 in 4200 live born males, it is one of the most frequent neuromuscular disorders. 2 Clinical signs and symptoms Initial complaints in most boys with DMD are an abnormal gait with toe walking, frequent falls and difficulties with climbing stairs. There is often a history of delayed achievement of motor milestones. The mean age at diagnosis is between 4 and 5 years 3,4,5 when proximal muscle weakness is sufficiently severe to produce a waddling gait and problems with rising from the floor. On physical examination one may find mild proximal muscle weakness in the lower limbs with a Gowers sign, shortened ankle tendons and tendon reflexes that are still present. There is compensatory lumbar hyperlordosis, which disappears when the child is sitting. The calf muscles are large and feel quite firm or even rubbery due to replacement of muscle fibres by fibrofatty tissue. Besides muscle weakness mental impairment can be present in DMD. 6 Approximately 33% of the patients has an intelligence quotient - score below Due to the progressive nature of the muscle disease, there is a linear decline in muscle strength making the children wheelchair bound at a mean age of 9,5 years. 8 Scoliosis is a frequent complication that may require surgical intervention. Nocturnal hypoventilation may be the first sign of respiratory insufficiency. If present, the child awakens frequently, is afraid of sleep and has headaches in the early morning. Signs of cardiomyopathy are already present in 25% of patients under 6 years, up to 59% in those between ages 6 and 10, without giving any symptoms. 9 Eventually, DMD patients die from respiratory insufficiency due to intercurrent infection or aspiration, or from cardiac arrhythmia. Patients who do not receive artificial ventilation from an early stage die at a mean age of 19 years, those who are ventilated at a mean age of 25 years. 1 Pathophysiology DMD is caused by mutations of the dystrophin gene which is located on the short arm of the X-chromosome (Xp21). 10 The protein product, called dystrophin, is situated at the sarcolemma in muscle fibres 11,12 and is part of the dystrophin-glycoprotein-complex 12

4 (DGC). 13 The DGC provides a structural link between the actin cytoskeleton and the extracellular matrix, thereby stabilising the sarcolemma during cycles of muscle contraction and relaxation. 14 However, the precise mechanism by which dystrophin deficiency causes the destruction of muscle fibres is still unknown. Diagnosis The diagnosis of DMD is based on clinical signs and symptoms and confirmed by raised serum concentration of creatine kinase (CK), 15 absence of dystrophin in muscle biopsy, 16 and the finding of a mutation in the dystrophin gene. In all DMD patients serum CK is raised from birth onwards and exceeds at least 10 times the normal upper limit. 15 After 5 years of age the concentration slowly declines. The muscle biopsy shows abnormalities typical of muscular dystrophy such as necrosis and attempted regeneration of individual muscle fibres, increased variability of muscle fibre diameter with both hypertrophic and small fibres, and central nuclei. (Figure 1). In an end-stage biopsy, almost the entire muscle is replaced by fibrofatty tissue. To confirm the clinical diagnosis immunohistochemical analysis of the muscle biopsy is usually performed. If this shows complete absence or severe reduction of dystrophin with only an occasional fibre (less than 5%) staining positively, 16 further genetic analysis is performed. DMD must be differentiated from Becker muscular dystrophy (BMD), which is caused by mutations in the same gene but has a milder phenotype. Genetics Mutations in the dystrophin gene can cause DMD or BMD. This is explained by the reading frame hypothesis 17 which states that mutations that maintain the reading frame (in-frame mutations) generally result in abnormal but partly functional dystrophin and usually cause BMD. 18 In DMD patients however, mutations disrupt the reading frame (frame-shift mutations), which eventually leads to dystrophin deficiency. In DMD and BMD, 65% of the pathogenic changes are large partial deletions 19,20 usually deleting multiple exons and 5% are partial duplications 19,21 of one or more exons. Both can be detected by quantitative multiplex PCR or Southern blot analysis. These partial deletions/duplications are clustered in two hot-spot regions of the gene, one proximal region comprising exons 2-20 and one more distal region comprising exons in the gene. 19 Part of the remaining 35% of pathogenic changes are most likely explained by small duplications or deletions that are often missed by the 13

5 Figure 1. Muscle biopsy from a 5 years old DMD patient. techniques mentioned earlier. These small changes can be detected, however, by one of many different pre-screening methods or direct sequencing. One of the most sensitive methods is denaturing gradient gel electrophoresis (DGGE) which has a detection rate of almost 100%. 22,23 Therapy There is no cure for DMD. Treatment goals are to maintain function, prevent contractures, and provide psychological support to the child and its family. Main efforts should be directed towards keeping these children standing and walking as long as possible. Passive stretching exercises, use of splints to maintain the feet in a neutral position during the night, and use of long-leg braces for walking are important in this respect. Scoliosis can not be prevented and, if progressive, surgical correction is the only effective way to straighten the spine. Steroids do have a beneficial effect on muscle force and muscle function, but their use is not yet generally accepted because of uncertainties about both the positive and negative effects on the long run. Other treatments aiming at the correction of the gene defect itself are not yet available for clinical use. 14

6 Outline of the thesis This thesis consists of two parts. The first part (Chapters 2-5) describes the results of diagnostic studies concerning muscle force, functional ability, calf circumference and ultrasonographic findings in DMD patients and healthy controls. Establishing reference values is important for several reasons such as for diagnostic purposes, for determining the extent and progression of the disease, and for evaluating possible effects of certain treatments. The second part of this thesis (Chapter 6-7) deals with the issue of prednisone therapy in DMD. Chapter 1, gives a short overview of the clinical, pathological and genetic aspects of DMD. In Chapter 2, reference values for maximum muscle force in normal children are described. In Chapter 3, these reference values are applied in ambulant DMD patients to assess the extent of muscle weakness and functional impairment. In Chapter 4, the extent of calf enlargement in ambulant DMD patients is compared with that in healthy controls. In Chapter 5, a complete set of quantitative ultrasonographic findings in biceps and quadriceps muscles of healthy children is presented. These data are applied in children with proven neuromuscular disease to evaluate their additional diagnostic value. In Chapter 6, a review of all aspects considering steroid treatment in DMD is given, based on the available literature. In Chapter 7, the results of a randomised controlled trial of the effects of prednisone on muscle function and the quality of life in ambulant DMD patients are presented. Finally, a summary and conclusions concerning this thesis are given. 15

7 Reference List 1. Eagle M, Baudouin SV, Chandler C et al. Survival in Duchenne muscular dystrophy: improvements in life expectancy since 1967 and the impact of home nocturnal ventilation. Neuromuscul. Disord. 2002;12: Essen van AJ, Busch HF, Meerman te G J et al. Birth and population prevalence of Duchenne muscular dystrophy in The Netherlands. Human Genetics. 1992;88: Mohamed K, Appleton R, Nicolaides P. Delayed diagnosis of Duchenne muscular dystrophy. Europ. J. Paediatr. Neurol. 2000;4: Crisp DE, Ziter FA, Bray PF. Diagnostic delay in Duchenne s muscular dystrophy. JAMA. 1982;247: Felisari G, Martinelli Boneschi F, Bardoni A et al. Loss of Dp140 dystrophin isoform and intellectual impairment in Duchenne dystrophy. Neurology. 2000;55: Cohen HJ, Molnar GE, Taft GE. The genetic relationship of progressive muscular dystrophy (Duchenne type) and mental retardation. Dev. Med. Child. Neurol. 1968;10: Bresolin N, Castelli E, Comi GP et al. Cognitive impairment in Duchenne muscular dystrophy. Neuromuscul. Disord. 1994;4: Essen van AJ, Verhij JBGM, Reefhuis J et al. The natural history of Duchenne muscular dystrophy. Analysis of data from Dutch survey and review of age related events. Thesis AJ van Essen 1997; Chapter 3;49-68: ISBN Nigro G, Comi LI, Politano L et al. The incidence and evolution of cardiomyopathy in Duchenne muscular dystrophy. Int. J. Cardiol. 1990;26: Monaco AP, Kunkel LM. Cloning of the Duchenne/Becker muscular dystrophy locus. Adv. Hum. Genet. 1988;17: Zubrzycka-Gaarn EE, Bulman DE, Karpati G et al. The Duchenne muscular dystrophy gene product is localized in sarcolemma of human skeletal muscle. Nature. 1988;333: Bonilla E, Samitt CE, Miranda AF et al. Duchenne muscular dystrophy: deficiency of dystrophin at the muscle cell surface. Cell. 1988;54: Campbell KP, Kahl SD. Association of dystrophin and an integral membrane glycoprotein. Nature. 1989;338: Petrof BJ, Shrager JB, Stedman HH et al. Dystrophin protects the sarcolemma from stresses developed during muscle contraction. Proc. Natl. Acad. Sci. USA 1993;90: Zatz M, Rapaport D, Vainzof M et al. Serum creatine-kinase (CK) and pyruvate-kinase (PK) activities in Duchenne (DMD) as compared with Becker (BMD) muscular dystrophy. Neurol. Sci. 1991;102: Bakker E, Jennekens F, Visser de M et al. European Neuro Muscular Centre. Diagnostic Criteria for Neuromuscular Disorders. London: Royal Society of Medicine Press, 1997: Monaco AP, Bertelson CJ, Liechti-Gallati S et al. An explanation for the phenotypic differences between patients bearing partial deletions of the DMD locus. Genomics. 1988;2:

8 18. Koenig M, Beggs AH, Moyer M et al. The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion. Am. J. Hum. Genet. 1989;45: Den Dunnen JT, Grootscholten PM, Bakker E et al. Topography of the Duchenne muscular dystrophy (DMD) gene: FIGE and cdna analysis of 194 cases reveals 115 deletions and 13 duplications. Am. J. Hum. Genet. 1989;45: Koenig M, Hoffman EP, Bertelson CJ et al. Complete cloning of the Duchenne muscular dystrophy (DMD) cdna and preliminary genomic organization of the DMD gene in normal and affected individuals. Cell. 1987;50: Hu XY, Ray PN, Murphy EG et al. Duplicational mutation at the Duchenne muscular dystrophy locus: its frequency, distribution, origin, and phenotypegenotype correlation. Am. J. Hum. Genet. 1990;46: Guldberg P, Guttler F. A simple method for identification of point mutations using denaturing gradient gel electrophoresis. Nucleic Acids Res. 1993;21: Guldberg P, Henriksen KF, Guttler F. Molecular analysis of phenylketonuria in Denmark: 99% of the mutations detected by denaturing gradient gel electrophoresis. Genomics. 1993;17:

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