Significance of genetic testing for paternal

Transcription

1 Significance of genetic testing for paternal uniparental disomy of chromosome 6 in neonatal diabetes mellitus Susan L. Christian, PhD, Barry H. Rich, MD, Charli Loebl, MS, Jeannette Israel, MD, Rohitkumar Vasa, MD, Kirk Kittikamron, BS, Rhonda Spiro, MD, Robert Rosenfield, MD, and David H. Ledbetter, PhD Two patients who presented at birth with neonatal diabetes mellitus (NDM) are described: one with paternal uniparental disomy for chromosome 6 and one with normal, biparental inheritance. The first child presented with low birth weight, macroglossia, hypertelorism, and club foot in addition to NDM. In this patient hyperglycemia was transient, and insulin treatment was discontinued at 4 months of age. The second child also presented with low birth weight but was normal in appearance, and insulin dependence continues after 5 years. Genetic analysis with polymorphic DNA markers for chromosome 6 indicated the presence of paternal uniparental disomy (UPD) in the first case and normal, biparental inheritance in the second case. Paternal UPD 6 has been reported in 8 previous cases of which 6 showed NDM. Three cases with paternal UPD 6 also included additional anomalies, such as macroglossia, not usually associated with NDM. Therefore the simultaneous finding of NDM and macroglossia should be a strong indicator for genetic testing. The genetic finding of paternal UPD 6 allows prediction of a transient, rather than permanent, form of diabetes mellitus and no increased recurrence risk of transient NDM in subsequent pregnancies. (J Pediatr 1999;134:42-6) Neonatal diabetes mellitus has been defined as hyperglycemia within the first month of life that lasts for at least 2 weeks and requires insulin therapy. 1 The incidence of NDM has been estimated at between 1:400,000 to 1:600,000 live births, and it may be ei- ther transient or permanent. 1,2 Other characteristics frequently observed in addition to neonatal diabetes include intrauterine growth retardation and failure to thrive; whereas macroglossia, umbilical hernia, and inguinal hernia have been observed in rare cases. 3-5 From the Departments of Human Genetics and Pediatrics, The University of Chicago, Illinois; Mercy Hospital, Chicago, Illinois; and Hope Children s Hospital, Oak Lawn, Illinois. Submitted for publication June 12, 1998; revision received Sept 4, 1998; accepted Sept 22, Reprint requests: David H. Ledbetter, PhD, Department of Human Genetics, The University of Chicago, 924 East 57th St, Chicago, IL Copyright 1999 by Mosby, Inc /99/$ /21/94580 The diabetic condition may be transient, permanent, or transient with a recurrence later in life. However, there are few data to differentiate between these subtypes in the neonatal period, which would aid the clinician in the likely prognosis. See editorial, p. 9. IUGR Intrauterine growth retardation NDM Neonatal diabetes mellitus PNDM Permanent neonatal diabetes mellitus TNDM Transient neonatal diabetes mellitus UPD Uniparental disomy UPD6pat Paternal uniparental disomy for chromosome 6 The genetics of NDM is poorly understood, and multiple genetic mechanisms are possible. However, there is now a strong association between transient neonatal diabetes mellitus and abnormalities of chromosome 6. Paternal uniparental disomy for chromosome 6 (UPD6pat) has been reported in 8 previous cases, 6 of which presented with TNDM. 2,6-8 Uniparental disomy, the inheritance of both copies of a chromosome from only one parent, is associated with maternal meiosis I nondisjunction events caused by advanced maternal age. 9 Paternal UPD is thought to arise from a postzygotic duplication of a monosomic conception. The presence of imprinted genes on a chromosome, that is, genes differentially expressed depending on the parental 42

2 THE JOURNAL OF PEDIATRICS VOLUME 134, NUMBER 1 CHRISTIAN ET AL origin of the chromosome, may then cause disease expression when UPD is present. 9 We have recently studied 2 children with NDM, one with a transient course and one with permanent neonatal diabetes mellitus. Fig 1. Patient 1 as a newborn. CASE REPORTS Patient 1 A male infant was born by cesarean section at 36 weeks gestation to a 39- year-old woman (gravida 4, para 3, abortion 1) of mixed European descent. The father was 5 9 tall and the mother 5 1. The mother did not have gestational diabetes and had no family history of diabetes. Because of advanced maternal age, amniocentesis was performed and revealed a normal 46,XY male karyotype. Pregnancy was complicated by poor growth from 28 weeks and oligohydramnios. Apgar scores were 9 and 9 at 1 and 5 minutes, respectively, and no resuscitation was necessary. The infant was admitted to the special care nursery soon after birth because of respiratory distress. The infant weighed 1844 g (10th centile), the length was 43 cm (10th centile), and head circumference was 31 cm (20th centile). Physical examination was significant for severe lack of subcutaneous fat and muscle mass, macroglossia, thin upper lip with a flat philtrum, upturned nose (Fig 1), high square forehead, overlapping helix of the ears, and hyperextensible and hypotonic lower extremities with talipes equinovarus of the right foot. Results of high-resolution chromosome analysis were normal. In the nursery the infant was noted to have elevated blood sugar levels up to 442 mg/dl on the second day of life. Hyperglycemia was treated with 2 doses of subcutaneous regular insulin and appeared to subside, although the child was treated with low-glucose (2.5%) intravenous solutions until the fifth day of life. Subsequently, the child gained weight poorly on oral feedings. On day 14 the blood sugar was noted to be 692 mg/dl. There was neither ketonuria nor acidosis. Further endocrine evaluation was not significant for any other underlying primary endocrine pathology, and the infant was treated with mixed, diluted human neutral protamine Hagedorn (3 injections daily) and regular insulin. Proinsulin (<0.12 pmol/l) and C-peptide (<0.01 pm/ml) levels, determined while the patient was hyperglycemic on day 15, were very low. The infant was subsequently discharged home at approximately 1 month of age on a regimen of neutral protamine Hagedorn insulin, 3 times daily, and regular insulin. Glucose control was maintained with a total insulin dose of 1 to 1.2 U/kg/d for the first 2 months of life. By 3 months of age, the child was euglycemic on every preprandial glucose determination, and the insulin dose was reduced. Insulin therapy was discontinued at 4 months, and hemoglobin A 1c (5.2%) was normal at 5 months and remains normal. On physical examination the infant s length was 63.3 cm (between the 10th and 25th centiles), weight was 6.7 kg (with a cast) (25th centile), and head circumference was 42.2 cm (between 25th and 50th centiles). Outer canthal distance was 8.25 cm (>97th centile), and inner canthal distance was 3.35 cm (97th centile). The macroglossia present at birth appeared somewhat diminished as Fig 2. DNA polymorphism analysis of chromosome 6. Case 1 is presented in the left panel with the polymorphic marker D6S477.The father is heterozygous with alleles 1 and 2, and the mother is heterozygous with alleles 1 and 3; the patient shows a single allele 2, indicating UPD for chromosome 6. Case 2 is presented in the right panel with the polymorphic marker D6S276.The father is heterozygous with alleles 2 and 3, and the mother is heterozygous with alleles 1 and 4; the patient shows alleles 1 and 2, indicating normal, biparental inheritance. TNDM resolved and catch-up growth was achieved. Patient 2 A 2.26 kg male infant was born at 39 weeks gestation to a 23-year-old woman (gravida 1, para 1) by normal spontaneous vaginal delivery. Apgar scores were 9 and 9 at 1 and 5 minutes, respectively. There was no history of gestational diabetes; however, the family history was significant for type 2 diabetes mellitus in the maternal grandmother and maternal great grandmother. Both parents were of normal height. 43

3 CHRISTIAN ET AL THE JOURNAL OF PEDIATRICS JANUARY 1999 Table. Microsatellite markers analyzed The infant did not appear dysmorphic, and no abnormality was observed on physical examination. The child made normal neonatal progress and was discharged on the second hospital day. He initially did well with breast-feeding, and his weight increased to 2.4 kg by day 10. At 8 days of age the umbilical cord fell off, but persistent drainage was noted from the umbilicus. At 11 days of age he was seen by his pediatrician because of erythema about and unusual drainage from the umbilicus. He was admitted to the hospital and began receiving parenteral antibiotic therapy for omphalitis. Admission laboratory studies showed a blood glucose level of 551 mg/dl. No ketones were present in urine, and the child was not acidotic. The hyperglycemia was initially considered to be secondary to stress and was treated with fluid management and no supplemental insulin. Despite improvement in the appearance in the umbilicus, the hyperglycemia persisted over the next 2 days. On the third hospital Patient 1 Patient 2 Locus F Pt M Result Locus F Pt M Result pter pter D6S Pat UPD D6S Bip D6S D6S Bip D6S Pat UPD D6S Pat UPD D6S Bip D6S D6S D6S Pat UPD D6S Pat UPD D6S Pat UPD D6S D6S Pat UPD D6S Bip D6S Pat UPD D6S Bip D6S Pat UPD D6S Bip D6S Pat UPD D6S Pat UPD D6S D6S Pat UPD D6S Pat UPD D6S Bip qter qter F, Father; Pt, patient; M, mother; Pat UPD, paternal uniparental disomy; Bip, biparental; pter, terminal end of short arm of chromosome 6; qter, terminal end of long arm of chromosome 6. day an insulin drip (0.05 U/kg/h) was started, and the infant was transferred to The University of Chicago Hospitals. Physical examination demonstrated a normal-appearing infant. Initially, insulin supplementation up to 2.5 U/kg/d was required to control glucose levels. After blood sugar control was achieved, the child was weaned from the continuous insulin infusion to subcutaneous insulin (1 to 1.6 U/kg/d). At home the insulin requirement fell progressively over the first month of therapy to ~0.6 U/kg/day; however, the child could not be completely weaned. Home monitoring continued to show variation in blood glucose levels; the child continuously required insulin of at least 0.3 U/kg/d. The child continues to receive insulin therapy after 5 years. METHODS For DNA polymorphism analysis, blood samples were obtained from each patient and both parents. Whole-cell lysates were prepared from peripheral blood by using the QIAamp blood lysis kit (Qiagen Inc, Santa Clarita, Calif). Microsatellite markers were selected based on their localization along chromosome 6, and primer pairs were acquired from Research Genetics (Huntsville, Ala). The polymerase chain reactions were set up in a total volume of 10 µl. The reaction mixture contained 10 mmol/l Tris-HCl at ph 8.4, 50 mmol/l KCl, 1.5 mmol/l MgCl 2, 200 µmol/l of each deoxynucleotide triphosphate, and 0.5 units Amplitaq Gold (Perkin- Elmer). To this mixture was added 0.2 µmol/l γ-phosphorus 32-adenosine triphosphate labeled forward primer and 0.2 µmol/l unlabeled reverse primer. For each marker 3 reactions were set up; and 1 µl of lysate from father, patient, and mother was added to 9 µl of reaction mix. Polymerase chain reaction analysis was performed by using a Perkin- Elmer 9600 thermocycler. Initial denaturation was performed at 95 C for 10 minutes, followed by 35 cycles at 94 C for 30 seconds, annealing at 55 C for 30 seconds, and extension at 72 C for 30 seconds. Final extension was accomplished at 72 C for 5 minutes. Samples were separated on 6% acrylamide/5.6 mol/l urea/32% formamide gel and run for 2 to 3 hours at 50 o C. The wet gels were exposed on Kodak XAR-5 film for 1 to 18 hours at 70 C with 2 intensifying screens. RESULTS The results of the DNA polymorphism analysis, with microsatellite markers extending along the length of chromosome 6, are presented in the Table for each patient and both parents. Patient 1 shows inheritance of a single paternal allele for 13 informative markers of 16 studied (Table, Fig 2). The other 3 microsatellite markers also showed a single allele but were not 44

4 THE JOURNAL OF PEDIATRICS VOLUME 134, NUMBER 1 CHRISTIAN ET AL fully informative because of sharing of parental alleles. However, in no instance did the child demonstrate inheritance of an allele present in the mother that was not also present in the father. Together with the normal cytogenetic analysis, these results indicate the presence of 2 copies of the paternal chromosome 6 (ie, uniparental disomy) and a complete failure to inherit a maternal chromosome 6. Additionally, because all markers show a single paternal allele over the entire length of the chromosome, the child inherited 2 identical copies of the same chromosome 6 from the father, which is referred to as complete isodisomy. In contrast, patient 2 showed only normal, biparental results for 7 of the 9 polymorphic microsatellite markers studied in this family (Table, Fig 2). The other 2 markers were uninformative with inheritance of alleles shared by each parent. DISCUSSION NDM is a rare condition usually observed in conjunction with IUGR. 10 In those cases with TNDM, only 18% of patients required insulin for more than 6 months, and the longest observed duration has been 18 months. 11 Approximately one third to one half of the patients proved to have PNDM. 1,12,13 Macroglossia in an infant with TNDM and IUGR was initially described by Dacou-Voutetakis et al 14 in These authors identified 2 additional cases in the literature 3,15 and suggested that TNDM, IUGR, and macroglossia may represent a new syndrome. 14 Subsequently, 6 other infants, in addition to our Patient 1, have been reported with the simultaneous findings of TNDM, IUGR, and macroglossia. 2,4,5,8 Additional anomalies in these cases included right inguinal hernia 3 ; anemia and umbilical hernia 4 ; and asymmetric growth retardation, large fontanelles, hypospadias, umbilical hernia, and bilateral inguinal hernias. 5 Molecular analysis of 5 cases showed the presence of UPD6pat in 3 cases 2,8 (patient 1 this report), a paternal interstitial duplication of 6q22-q23 in one case, 16 and normal, biparental inheritance in one case from a firstcousin marriage. 2 Recent follow-up studies on several patients with TNDM have demonstrated resumption of a diabetic state, in some instances insulin-resistant, in late childhood or adolescence. 11,17-20 However, UPD studies have not been performed in these cases. Long-term follow-up of one patient with UPD6pat showed recurrence of diabetes requiring insulin therapy at 13 years of age, 2,21 whereas the patients in the other reported cases are currently too young to rule out recurrence at a later age. Only rarely has NDM been reported with other dysmorphic features suggestive of a specific syndrome. Wolcott-Rallison syndrome, which includes permanent diabetes mellitus and multiple epiphyseal dysplasia or spondyloepiphyseal dysplasia, is an autosomal recessive genetic disorder. 22 Low birth weight is not a prominent feature, and onset of diabetes generally occurs after the first month of life. The limb abnormalities present in this syndrome clearly differentiate it from the TNDM observed with UPD6pat. Although UPD is a sporadic event with a low recurrence risk, familial cases of TNDM have also been reported Affected siblings have been observed in ~26% of PNDM and 28% of TNDM cases. 13 In one family 3 siblings with the same father and 3 different mothers were born with TNDM. 26,27 One of these siblings showed recurrence of diabetes mellitus requiring insulin therapy at 15 years of age, whereas a second sibling was healthy at 19 years. 27 NDM has also been observed in first cousins: one child showed TNDM and the other PNDM, 28 suggestive of additional modes of inheritance involved in NDM. The gene or genes causing TNDM are still unknown; however, the candidate region on chromosome 6 has been refined to the q22-q23 region. 29 One gene involved in glucose metabolism, the membrane glycoprotein PC-1, an inhibitor of insulin-receptor tyrosine kinase, is located within this region and has been suggested to have a role in insulin resistance and type 2 diabetes. 30 However, the importance of this gene in the occurrence of later type 2 diabetes in some of these patients might be easier to explain than the role for this gene in the initial presentation with insulin deficiency. NDM is a rare disorder with multiple modes of inheritance and multiple outcomes. Identifying patients with UPD6pat allows the clinician to predict a transient, rather than permanent, course for diabetes mellitus. Additionally, the recurrence risk of UPD in subsequent pregnancies would be predicted to be low. Although one patient with UPD6pat has been confirmed to show recurrence of diabetes mellitus at a later age, additional patients require long-term follow-up to determine whether recurrence of diabetes mellitus occurs on a consistent basis. REFERENCES 1. von Mühlendahl KE, Herkenhoff H. Long-term course of neonatal diabetes. N Engl J Med 1995;333: Shield JPH, Gardner RJ, Wadsworth EJK, Whiteford ML, James RS, Robinson DO, et al. Aetiopathology and genetic basis of neonatal diabetes. Arch Dis Child 1997;76:F39-F Gerrard JW, Chin W. The syndrome of transient diabetes. J Pediatr 1962;61: Salerno M, Gasparini N, Sandomenico ML, Franzese A, Tenore A. Two interesting cases of transient neonatal diabetes mellitus. J Pediatr Endocrinol 1994;7: Battin M, Yong C, Phang M, Daaboul J. Transient neonatal diabetes mellitus and macroglossia. J Perinatol 1996;16: Temple IK, James RS, Crolla JA, Sitch FL, Jacobs PA, Howell WM, et al. An imprinted gene(s) for diabetes? Nat Genet 1995;9:

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