Myoclonus-dystonia and Silver Russell syndrome resulting from maternal uniparental disomy of chromosome 7

Transcription

1 Clin Genet 2013: 84: Printed in Singapore. All rights reserved Short Report 2012 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd CLINICAL GENETICS doi: /cge Myoclonus-dystonia and Silver Russell syndrome resulting from maternal uniparental disomy of chromosome 7 Sheridan MB, Bytyci Telegrafi A, Stinnett V, Umeh CC, Mari Z, Dawson TM, Bodurtha J, Batista DAS. Myoclonus-dystonia and Silver Russell syndrome resulting from maternal uniparental disomy of chromosome 7. Clin Genet 2013: 84: John Wiley & Sons A/S. Published by John Wiley & Sons Ltd, 2012 Myoclonus-dystonia (M-D) is a movement disorder that is often associated with mutations in epsilon-sarcoglycan (SGCE), a maternally imprinted gene at 7q21.3. We report a 24-year-old male with short stature (<5th percentile) and a movement disorder clinically consistent with M-D. Single nucleotide polymorphism (SNP) array did not identify significant copy number changes, but revealed three long continuous stretches of homozygosity on chromosome 7 suggestive of uniparental disomy. Parental SNP arrays confirmed that the proband had maternal uniparental disomy of chromosome 7 (mupd7) with regions of heterodisomy and isodisomy. mupd7 is the cause of approximately 5 10% of Silver Russell syndrome (SRS), a disorder characterized by prenatal and postnatal growth retardation. Although SRS was not suspected in our patient, these findings explain his short stature. SGCE methylation testing showed loss of the unmethylated paternal allele. Our findings provide a unifying diagnosis for his short stature and M-D and help to optimize his medication regimen. In conclusion, we show that M-D is a clinical feature that may be associated with SRS due to mupd7. Individuals with mupd7 should be monitored for the development of movement disorders. Conversely, individuals with M-D and short stature should be evaluated for SRS. Conflict of interest The authors confirm that there are no potential conflicts of interest with this manuscript. MB Sheridan a, A Bytyci Telegrafi a, V Stinnett b, CC Umeh c,zmari c,tm Dawson c,d, J Bodurtha a and DAS Batista a,b,e a McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA, b Cytogenetics and Microarray Laboratory, Kennedy Krieger Institute, Baltimore, MD, USA, c Department of Neurology, d Neuroregeneration Program, Institute for Cell Engineering and the Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA, and e Department of Pathology, Johns Hopkins University, Baltimore, MD, USA Key words: epsilon-sarcoglycan maternal uniparental disomy of chromosome 7 myoclonus-dystonia Silver Russell syndrome Corresponding author: Denise A.S. Batista, PhD, Cytogenetics Laboratory, Johns Hopkins University, 600 N. Wolfe St., Park Bldg. SB 202, Baltimore, MD 21287, USA. Tel.: ; fax: ; dbatist1@jhmi.edu Received 11 October 2012, revised and accepted for publication 10 December 2012 Myoclonus-dystonia (M-D; OMIM #159900) is a movement disorder characterized by bilateral, alcoholsensitive myoclonic jerks and dystonia typically diagnosed in the first 2 decades of life (1). The age of onset can range from 4 months to 75 years (2, 3). The M-D phenotype may include non-motor symptoms such as depression, obsessive compulsive disorder and panic attacks (4). It is associated with mutations in the epsilon-sarcoglycan gene (SGCE), located at 7q21.3 (5). SGCE is widely expressed with the highest levels in lung, heart, brain, and skeletal muscle (6). It is a component of the sarcoglycan complex in muscle, but a specific role for SGCE in the brain has not yet been described (7). SGCE is maternally imprinted and preferentially expressed from the paternal allele (8, 9). The inheritance pattern of M-D is autosomal dominant with variable penetrance dependent on the parent of origin of the mutation. Penetrance is nearly complete in paternal transmission and very rare in maternal transmission (10). Previously reported M-D-associated 368

2 Myoclonus-dystonia and Silver Russell syndrome mutations are predicted to cause loss of SGCE function (11). Mutations affecting the methylation status of SGCE have not been reported (1). Silver Russell syndrome (SRS; OMIM #180860) is characterized by intrauterine growth restriction and postnatal growth deficiency with proportionate short stature and normal head circumference (12). SRS is genetically heterogeneous with 30 60% of cases associated with hypomethylation of the paternal allele of imprinting center region (ICR1) at 11p15.5 (13), whereas approximately 5 10% of cases are due to maternal uniparental disomy of chromosome 7 (mupd7) (12). Patients with mupd7 should not express SGCE as they lack the paternal unmethylated SGCE allele. This genotype is consistent with an M-D phenotype, but abnormal movements are not part of the classically described SRS phenotype. There are, however, three previous reports of M-D-like movement disorders in five patients with SRS due to mupd7 (14 16). We report the sixth patient with SRS and M-D due to mupd7. Methods SNP array Blood samples were obtained from the proband, his brother, and parents with informed consent following the guidelines of the Institutional Review Board at the Johns Hopkins School of Medicine. Genomic DNA was extracted using the QIAamp kit (Qiagen, Valencia, CA) and single nucleotide polymorphism (SNP) array analysis was performed using the Illumina Human Omni1-Quad (1,000,000 markers) and the Illumina CytoSNP12 (300,000 markers) (Illumina, San Diego, CA). Allele ratios and signal intensity were analyzed with the CNV Partition algorithm in KaryoStudio (v ) and GenomeStudio (v ) (Illumina). Genotypes of SNPs on chromosome 7 from the proband and his parents were manually compared to determine the parent of origin of chromosome 7. Genomic positions are based on the February 2009 Human Genome Build (hg19). Karyotype and fluorescence in situ hybridization A high-resolution karyotyping was performed using phytohemagglutinin-stimulated blood lymphocytes following standard G-banding protocols. Fluorescence in situ hybridization (FISH) was performed on interphase nuclei using two commercially available probes on chromosome 7 (LSI D7S522,7q31 SpectrumOrange/CEP 7 SpectrumGreen Probe; Abbott Molecular, Des Plaines, IL). SGCE methylation DNA samples were treated with sodium bisulfite using the QiagenEpiTect Bisulfite Kit (Qiagen). A 197- nucleotide region in the SGCE promoter was amplified from 2 ng of bisulfite-converted DNA using the PyroMark PCR Kit (Qiagen) and a commercially available biotinylated SGCE PCR primer pair (Pyro- MarkCpG Assay PM ; Qiagen) according to the manufacturer s specifications. The resulting nonbiotinylated strand was sequenced on a Pyromark Q24 system (Qiagen). Case report The proband is a 24-year-old man with short stature evaluated for jerking of the arms and shoulders with unknown etiology. He was born at 42 weeks gestation and was small for gestational age at 2.3 kg (<3rd percentile). His adult height (151.9 cm) and weight (52.7 kg) are both below the fifth percentile and he is significantly shorter than his parents (midparental percentile: 25 50th percentile). The proband was macrocephalic (56 cm, >90th percentile). Dysmorphic features included mild frontal bossing, triangular face, deep set eyes, mild fifth finger clinodactyly, arm length discrepancy and three café au lait spots. There was no history of developmental delay or school difficulties. His brother also has short stature ( cm, <5th percentile) without abnormal movements. The patient s abnormal movements began at about 7 years of age as difficulty in writing and throwing. He currently has intermittent, action-induced myoclonic jerking of both his hands and arms and transient actioninduced dystonic posturing of his hands and arms. The frequency of his abnormal movements decreases with alcohol intake. He has a history of anxiety attacks. His symptoms were substantially reduced by clonazepam. Results SNP array showed a male genotype with no significant copy number changes. However, there were three long continuous stretches of homozygosity on chromosome 7 (Fig. 1a,b). Two segments were on the short arm between bands 7p22.3 7p21.3 and 7p21.3 7p13 from nucleotide 10,704 (the first SNP on this platform) to 8,249,663 and 9,173,694 to 44,142,792, respectively. The third stretch of homozygosity was on the long arm of chromosome 7 between bands 7q21.3 and 7q31.33 from nucleotide 97,616,154 to 125,604,657. No other large regions of homozygosity were seen. Large homozygous region(s) confined to one chromosome are suggestive of chromosomal uniparental disomy with regions of isodisomy and heterodisomy. To test this hypothesis, the proband and both of his parents were genotyped using an Illumina 300K array that contained 15,344 SNPs on chromosome 7. The genotypes of the 7065 SNPs present in the regions of loss of heterozygosity (LOH) were consistent with maternal isodisomy. The 8279 SNPs outside of the LOH regions were identical between the proband and his mother at all but one SNP. This one discordant SNP was determined to be a genotyping error in the patient s mother. Collectively, these data are consistent with mupd7 with segments of heterodisomy and 369

3 Sheridan et al. (a) (b) Fig. 1. Illumina Omni1-Quad single nucleotide polymorphism (SNP) array indicates three regions with loss of heterozygosity (LOH) on chromosome 7. (a) B allele frequencies of single SNPs across the entire length of chromosome 7 are represented as data points. The three regions of LOH lack heterozygous (AB) calls and are shaded in light gray. Arrows indicate the locations of the five crossover events. (b) Log R ratio for individual probes on chromosome 7 is represented as data points. There are no significant copy number gains or losses on chromosome 7. These plots were generated using GenomeStudio software. isodisomy due to five meiotic crossover events on chromosome 7. A high-resolution chromosome analysis showed a normal male karyotype. FISH showed no evidence of chromosome 7 trisomy in 508 interphases examined. The patient s brother with short stature was also genotyped using SNP array and showed biparental inheritance of chromosome 7. Because of the patient s M-D-like phenotype, we assessed the methylation status of SGCE. We predicted that his SGCE promoter would be completely methylated because he carries two maternal SGCE alleles. DNA samples from both of the proband s parents as well as his brother were used as controls. We used sodium bisulfite treatment followed by pyrosequencing to determine the methylation status of four CpG residues within the SGCE promoter in these four individuals (Fig. 2a). These residues are part of a differentially methylated CpG island that extends 1117 nucleotides upstream and 552 nucleotides downstream of SGCE (8). In individuals with biparental inheritance of chromosome 7, approximately 50% of the CpG residues at these four loci should be methylated. This was the pattern observed in the controls (Fig. 2b). Conversely, these four residues were % methylated in the proband. These data confirm that the SGCE promoter is fully methylated in the proband, consistent with M-D. Discussion Utilizing SNP array, we identified extended regions of homozygosity on chromosome 7 in a patient with short stature and M-D. Parental analysis of SNP array genotyping showed that the patient had mupd7 with segments of isodisomy and heterodisomy. This scenario can be explained by the occurrence of five crossover events followed by a segregation error leading to an aneuploid oocyte. Because there are pericentromeric heterozygous SNPs, this event probably occurred during maternal meiosis I (17). The high number of crossovers and relative proximity of one to the centromere may have led to entanglement of the maternal meiotic bivalent resulting in either non-disjunction or precocious separation of sister chromatids (18). This aneuploid gamete, when fertilized, resulted in a zygote with trisomy 7 and subsequent loss of the paternal chromosome 7 homolog by trisomy rescue. No cells with trisomy 7 were identified in the patient s lymphocytes, suggesting that this trisomy rescue event occurred very early in development. Although the diagnoses of SRS or M-D had not been previously considered in this patient, the identification of mupd7 provides a unifying diagnosis for his physical features and movement disorder. His short stature, relative macrocephaly, facial features, mild fifth finger clinodactyly, and arm length discrepancy are all consistent with SRS. Similarly, his myoclonus and dystonia that began at age 7 is typical for M-D due to loss of SGCE expression. He was initially prescribed clonazepam to control his abnormal movements, but recently began having more frequent symptoms and was switched to carbamazepine. Following the diagnosis of M-D, his medication was switched back to a higher dose of clonazepam, as this has been reported to be an effective treatment for myoclonic jerks as seen in M-D (19, 20). Decreased severity of symptoms with alcohol consumption, as observed in our patient, is a hallmark feature of M-D (5). Additionally, M-D is consistent 370

4 Myoclonus-dystonia and Silver Russell syndrome (a) (b) Fig. 2. Loss of the unmethylated SGCE allele in the proband. (a) A diagram of the genomic location of the CpG island in the SGCE promoter. The methylation status of the four underlined CpG dinucleotides was assessed in the patient and his family members using sodium bisulfite treatment followed by pyrosequencing. This graphic was constructed using the UCSC Genome Browser (GRCh37/hg19). (b) Summary of SGCE promoter CpG methylation studies. with the patient s panic attacks as individuals with M-D have been described to have an increased frequency of psychiatric features including anxiety disorders (4). A comprehensive search of the literature identified three additional reports of abnormal movements in SRS. The phenotypes of these five patients are described in Table 1. All patients with mupd7 should lack SGCE expression due to loss of the paternal SGCE allele, yet our patient is only the sixth to have been described with M-D-like features. The fact that mupd7 accounts for only 5 10% of SRS explains why abnormal movements are not a well-established feature of the SRS phenotype. Additionally, the majority of subjects with mupd7 who have been reported in the literature are young. M-D typically develops in the first or second decade of life (1), so it is possible that abnormal movements develop after the initial mupd7 diagnosis and evaluation. For example, myoclonic jerks and dystonia were only noted at 17 years in the mupd7 patient reported by Guettard et al. (14). Long-term follow-up may be necessary to determine the actual frequency of M-D in this population. There is also the potential for additional genetic or Table 1. Movement disorder phenotype of previously reported maternal uniparental disomy of chromosome 7 (mupd7) patients Age (years) mupd7 Age at presentation of movement disorder (years) Movement disorder phenotype References Guettard et al. (14) 36 + a 17 Shock-like myoclonic jerks of the upper limbs, trunk, and face; mild dystonia b 6 + <6 Generalized myoclonus with shock-like jerks of Stark et al. (15) all four extremities; no dystonia Intermittent episodes of head shaking Wakeling et al. (16) Slight tremor affecting left arm Wakeling et al. (16) + Myoclonic jerks in infancy (3 weeks to 1 year) Wakeling et al. (16) which resolved Intermittent, action-induced myoclonic jerking of both hands and arms; transient action-induced dystonic posturing of hands and arms Current report, data not available. a This patient had mupd7 and an abnormal mosaic karyotype (47,XY+mar[22]/46,XY[11]) with a small marker chromosome derived from chromosome 7. b mrna studies confirmed that this patient lacked SGCE expression. 371

5 Sheridan et al. environmental factors that could relax SGCE imprinting and lead to sufficient expression to allow for some mupd7 patients to escape the M-D phenotype. Despite only being reported in six patients, our findings illustrate that the presence of M-D differentiates SRS due to mupd7 vs other causes. Because of the variability of the age of onset of M-D this distinction may not be possible in young SRS patients. Nevertheless, this is important, as currently the genetic etiology of SRS cannot be predicted based on clinical features alone (16, 21). Moreover, similar to our patient, it is also possible that some individuals with M-D who have short stature could have undiagnosed SRS. Thus, testing for mupd7 in any patient with short stature and M-D should be considered. Acknowledgements We thank the members of the Kennedy Krieger Cytogenetics and Microarray and Johns Hopkins Cancer Cytogenetics laboratories, especially Elizabeth Wohler, Laura Morsberger and Patricia Long, for their technical support and Julie Hoover-Fong and Hans Bjornsson for helpful advice. Methylation studies were conducted at Genetic Resources Core Facility at Johns Hopkins University. Special thanks to the patient and his family for their participation. This work was supported by the NIH [5P30 HD (D. A. S. B.); NINDS NS38377 (T. M. D)]. T. M. D. is the Leonard and Madlyn Abramson Professor in Neurodegenerative Diseases. References 1. Kinugawa K, Vidailhet M, Clot F, Apartis E, Grabl D, Roze E. Myoclonus-dystonia: an update. Mov Disord 2009: 24 (4): Valente EM, Edwards MJ, Mir P et al. The epsilon-sarcoglycan gene in myoclonic syndromes. Neurology 2005: 64 (4): Foncke EM, Gerrits MC, van Ruissen F et al. Distal myoclonus and late onset in a large Dutch family with myoclonus-dystonia. Neurology 2006: 67 (9): Peall KJ, Waite AJ, Blake DJ, Owen MJ, Morris HR. Psychiatric disorders, myoclonus dystonia, and the epsilon-sarcoglycan gene: a systematic review. Mov Disord 2011: 26 (10): Zimprich A, Grabowski M, Asmus F et al. Mutations in the gene encoding epsilon-sarcoglycan cause myoclonus-dystonia syndrome. Nat Genet 2001: 29 (1): Ettinger AJ, Feng G, Sanes JR. Epsilon-sarcoglycan, a broadly expressed homologue of the gene mutated in limb-girdle muscular dystrophy 2D. J Biol Chem 1997: 272 (51): Ritz K, van Schaik BD, Jakobs ME et al. SGCE isoform characterization and expression in human brain: implications for myoclonus-dystonia pathogenesis? Eur J Hum Genet 2011: 19 (4): Grabowski M, Zimprich A, Lorenz-Depiereux B et al. The epsilonsarcoglycan gene (SGCE), mutated in myoclonus-dystonia syndrome, is maternally imprinted. Eur J Hum Genet 2003: 11 (2): Muller B, Hedrich K, Kock N et al. Evidence that paternal expression of the epsilon-sarcoglycan gene accounts for reduced penetrance in myoclonus-dystonia. Am J Hum Genet 2002: 71 (6): Tezenas du Montcel S, Clot F, Vidailhet M et al. Epsilon sarcoglycan mutations and phenotype in French patients with myoclonic syndromes. J Med Genet 2006: 43 (5): Grunewald A, Djarmati A, Lohmann-Hedrich K et al. Myoclonusdystonia: significance of large SGCE deletions. Hum Mutat 2008: 29 (2): Wakeling EL. Silver-Russell syndrome. Arch Dis Child 2011: 96 (12): Gicquel C, Rossignol S, Cabrol S et al. Epimutation of the telomeric imprinting center region on chromosome 11p15 in Silver-Russell syndrome. Nat Genet 2005: 37 (9): Guettard E, Portnoi MF, Lohmann-Hedrich K et al. Myoclonusdystonia due to maternal uniparental disomy. Arch Neurol 2008: 65 (10): Stark Z, Ryan MM, Bruno DL, Burgess T, Savarirayan R. Atypical Silver-Russell phenotype resulting from maternal uniparental disomy of chromosome 7. Am J Med Genet A 2010: 152A (9): Wakeling EL, Amero SA, Alders M et al. Epigenotype-phenotype correlations in Silver-Russell syndrome. J Med Genet 2010: 47 (11): Conlin LK, Thiel BD, Bonnemann CG et al. Mechanisms of mosaicism, chimerism and uniparental disomy identified by single nucleotide polymorphism array analysis. Hum Mol Genet 2010: 19 (7): Gabriel AS, Thornhill AR, Ottolini CS et al. Array comparative genomic hybridisation on first polar bodies suggests that nondisjunction is not the predominant mechanism leading to aneuploidy in humans. J Med Genet 2011: 48 (7): Kyllerman M, Forsgren L, Sanner G, Holmgren G, Wahlström J, Drugge U. Alcohol-responsive myoclonic dystonia in a large family: dominant inheritance and phenotypic variation. Mov Disord 1990: 5 (4): Kurlan R, Behr J, Medved L, Shoulson I. Myoclonus and dystonia: a family study. Adv Neurol 1988: 50: Kotzot D. Maternal uniparental disomy 7 and Silver-Russell syndrome - clinical update and comparison with other subgroups. Eur J Med Genet 2008: 51 (5):