High-resolution breakpoint junction mapping of proximally extended D4Z4 deletions in FSHD1 reveals evidence for a founder effect.

Facioscapulohumeral muscular dystrophy (FSHD) is an inherited myopathy clinically characterized by weakness in the facial, shoulder girdle and upper a muscles. FSHD is caused by chromatin relaxation of the D4Z4 macrosatellite repeat, mostly by a repeat contraction, facilitating ectopic expression of DUX4 in skeletal muscle. Genetic diagnosis for FSHD is generally based on the sizing and haplotyping of the D4Z4 repeat on chromosome 4 by Southern blotting (SB), molecular combing or single-molecule optical mapping, which is usually straight forward but can be complicated by atypical rearrangements of the D4Z4 repeat. One of these rearrangements is a D4Z4 proximally extended deletion (DPED) allele, where not only the D4Z4 repeat is partially deleted, but also sequences immediately proximal to the repeat are lost, which can impede accurate diagnosis in all genetic methods. Previously, we identified several DPED alleles in FSHD and estimated the size of the proximal deletions by a complex pulsed-field gel electrophoresis and SB strategy. Here, using the next-generation sequencing, we have defined the breakpoint junctions of these DPED alleles at the base pair resolution in 12 FSHD families and 4 control individuals facilitating a PCR-based diagnosis of these DPED alleles. Our resultsshow that half of the DPED alleles are derivates of an ancient founder allele. For some DPED alleles, we found that genetic elements are deleted such as DUX4c, FRG2, DBE-T and myogenic enhancers necessitating re-evaluation of their role in FSHD pathogenesis.

FSHD1 and FSHD2 form a disease continuum.

OBJECTIVE: To compare the clinical features of patients showing a classical phenotype of facioscapulohumeral muscular dystrophy (FSHD) with genetic and epigenetic characteristics of the FSHD1 and FSHD2 loci D4Z4 and SMCHD1. METHODS: This is a national multicenter cohort study. We measured motor strength, motor function, and disease severity by manual muscle testing sumscore, Brooke and Vignos scores, clinical severity score (CSS), and age-corrected CSS, respectively. We correlated these scores with genetic (D4Z4 repeat size and haplotype; SMCHD1 variant status) and epigenetic (D4Z4 methylation) parameters. RESULTS: We included 103 patients: 54 men and 49 women. Among them, we identified 64 patients with FSHD1 and 20 patients with FSHD2. Seven patients had genetic and epigenetic characteristics of FSHD1 and FSHD2, all carrying repeats of 9-10 D4Z4 repeat units (RU) and a pathogenic SMCHD1 variant. In the remaining patients, FSHD was genetically excluded or remained unconfirmed. All clinically affected SMCHD1 mutation carriers had a D4Z4 repeat of 9-16 RU on a disease permissive 4qA haplotype. These patients are significantly more severely affected by all clinical scales when compared to patients with FSHD1 with upper-sized FSHD1 alleles (8-10 RU). CONCLUSION: The overlap between FSHD1 and FSHD2 patients in the 9-10 D4Z4 RU range suggests that FSHD1 and FSHD2 form a disease continuum. The previously established repeat size threshold for FSHD1 (1-10 RU) and FSHD2 (11-20 RU) needs to be reconsidered. CLINICALTRIALSGOV IDENTIFIER: NCT01970735.

Copy number variations and founder effect underlying complete IL-10Rß deficiency in Portuguese kindreds.

Mutations in interleukin-10 receptor (IL-10R) genes are one cause of very early-onset inflammatory bowel disease with perianal lesions, which can be cured by hematopoietic stem cell transplantation. Using a functional test, which assesses responsiveness of peripheral monocytes to IL-10, we identified three unrelated Portuguese patients carrying two novel IL-10RB mutations. In the three patients, sequencing of genomic DNA identified the same large deletion of exon 3 which precluded protein expression. This mutation was homozygous in two patients born from consanguineous families and heterozygous in the third patient born from unrelated parents. Microsatellite analysis of the IL10RB genomic region revealed a common haplotype in the three Portuguese families pointing to a founder deletion inherited from a common ancestor 400 years ago. In the third patient, surface expression of IL-10R was normal but signaling in response to IL-10 was impaired. Complementary DNA sequencing and next-generation sequencing of IL10RB locus with custom-made probes revealed a ≈ 6 Kb duplication encompassing the exon 6 which leads to a frameshift mutation and a loss of the TYK2-interacting Box 2 motif. Altogether, we describe two novel copy number variations in IL10RB, one with founder effect and one preserving cell surface expression but abolishing signaling.

Targeted Exome Sequencing Identifies PBX1 as Involved in Monogenic Congenital Anomalies of the Kidney and Urinary Tract.

Congenital anomalies of the kidney and urinary tract (CAKUT) occur in three to six of 1000 live births, represent about 20% of the prenatally detected anomalies, and constitute the main cause of CKD in children. These disorders are phenotypically and genetically heterogeneous. Monogenic causes of CAKUT in humans and mice have been identified. However, despite high-throughput sequencing studies, the cause of the disease remains unknown in most patients, and several studies support more complex inheritance and the role of environmental factors and/or epigenetics in the pathophysiology of CAKUT. Here, we report the targeted exome sequencing of 330 genes, including genes known to be involved in CAKUT and candidate genes, in a cohort of 204 unrelated patients with CAKUT; 45% of the patients were severe fetal cases. We identified pathogenic mutations in 36 of 204 (17.6%) patients. These mutations included five de novo heterozygous loss of function mutations/deletions in the PBX homeobox 1 gene (PBX1), a gene known to have a crucial role in kidney development. In contrast, the frequency of SOX17 and DSTYK variants recently reported as pathogenic in CAKUT did not indicate causality. These findings suggest that PBX1 is involved in monogenic CAKUT in humans and call into question the role of some gene variants recently reported as pathogenic in CAKUT. Targeted exome sequencing also proved to be an efficient and cost-effective strategy to identify pathogenic mutations and deletions in known CAKUT genes.

Greater prevalence of PROKR2 mutations in Kallmann syndrome patients from the Maghreb than in European patients.

CONTEXT: Kallmann syndrome (KS) is a genetically heterogeneous developmental disorder that associates hypogonadotropic hypogonadism and anosmia. Various causative genes have been identified, but their respective involvement in different world regions is poorly documented. OBJECTIVE: We aimed to compare the prevalence of mutations in five routinely analyzed KS genes between Maghrebian and European patients. METHODS: Blood samples from 120 presumably unrelated Maghrebian patients were collected for DNA sequencing by the Sanger technique. The prevalence of the non-synonymous mutations in KAL1, FGFR1, FGF8, PROKR2, and PROK2 was determined for each gene, and compared with those previously obtained from the analysis of 712 European patients. RESULTS: Diverse mutations in PROKR2, a gene involved both in monogenic recessive and digenic/oligogenic KS transmission modes, were found in 23.3% of the Maghrebian patients, but only in 5.1% of the European patients (Fisher's exact test, P<0.001), whereas mutations in each of the other four KS genes were present either at similar frequencies in the Maghrebian and European patients (KAL1, PROK2, FGF8, from 6.6 to 0.8%; Fisher's exact test, P>0.4 for all comparisons) or at a lower frequency in Maghrebian patients (FGFR1, 5.0 vs 11.7%; Fisher's exact test, P<0.05). Homozygosity resulting from consanguineous marriages was not sufficient to account for the greater prevalence of PROKR2 mutations in the Maghrebian patients. CONCLUSIONS: The great prevalence of PROKR2 mutations in Maghrebian patients has practical consequences for molecular diagnosis of the disease and genetic counseling in the Maghrebian population.

An ancient founder mutation in PROKR2 impairs human reproduction.

Congenital gonadotropin-releasing hormone (GnRH) deficiency manifests as absent or incomplete sexual maturation and infertility. Although the disease exhibits marked locus and allelic heterogeneity, with the causal mutations being both rare and private, one causal mutation in the prokineticin receptor, PROKR2 L173R, appears unusually prevalent among GnRH-deficient patients of diverse geographic and ethnic origins. To track the genetic ancestry of PROKR2 L173R, haplotype mapping was performed in 22 unrelated patients with GnRH deficiency carrying L173R and their 30 first-degree relatives. The mutation's age was estimated using a haplotype-decay model. Thirteen subjects were informative and in all of them the mutation was present on the same ~123 kb haplotype whose population frequency is ≤10%. Thus, PROKR2 L173R represents a founder mutation whose age is estimated at approximately 9000 years. Inheritance of PROKR2 L173R-associated GnRH deficiency was complex with highly variable penetrance among carriers, influenced by additional mutations in the other PROKR2 allele (recessive inheritance) or another gene (digenicity). The paradoxical identification of an ancient founder mutation that impairs reproduction has intriguing implications for the inheritance mechanisms of PROKR2 L173R-associated GnRH deficiency and for the relevant processes of evolutionary selection, including potential selective advantages of mutation carriers in genes affecting reproduction.

Study of LPIN1, LPIN2 and LPIN3 in rhabdomyolysis and exercise-induced myalgia.

BACKGROUND: Recessive LPIN1 mutations were identified as a cause of severe rhabdomyolysis in pediatric patients. The human lipin family includes two other closely related members, lipin-2 and 3, which share strong homology and similar activity. The study aimed to determine the involvement of the LPIN family genes in a cohort of pediatric and adult patients (n = 171) presenting with muscular symptoms, ranging from severe (CK >10 000 UI/L) or moderate (CK <10 000 UI/L) rhabdomyolysis (n = 141) to exercise-induced myalgia (n = 30), and to report the clinical findings in patients harboring mutations. METHODS: Coding regions of LPIN1, LPIN2 and LPIN3 genes were sequenced using genomic or complementary DNAs. RESULTS: Eighteen patients harbored two LPIN1 mutations, including a frequent intragenic deletion. All presented with severe episodes of rhabdomyolysis, starting before age 6 years except two (8 and 42 years). Few patients also suffered from permanent muscle symptoms, including the eldest ones (≥ 40 years). Around 3/4 of muscle biopsies showed accumulation of lipid droplets. At least 40% of heterozygous relatives presented muscular myalgia. Nine heterozygous SNPs in LPIN family genes were identified in milder phenotypes (mild rhabdomyolysis or myalgia). These variants were non-functional in yeast complementation assay based on respiratory activity, except the LPIN3-P24L variant. CONCLUSION: LPIN1-related myolysis constitutes a major cause of early-onset rhabdomyolysis and occasionally in adults. Heterozygous LPIN1 mutations may cause mild muscular symptoms. No major defects of LPIN2 or LPIN3 genes were associated with muscular manifestations.

A founder effect at the EPCAM locus in Congenital Tufting Enteropathy in the Arabic Gulf.

Mutations of the EPCAM gene have been recently identified in Congenital Tufting Enteropathy (CTE), a severe autosomal recessive gastrointestinal insufficiency of childhood requiring parenteral nutrition and occasionally intestinal transplantation. Studying seven multiplex consanguineous families from the Arabic peninsula (Kuwait and Qatar) we found that most patients were homozygote for a c.498insC mutation in exon 5. The others carried a novel mutation IVS4-2A→G. Both mutations were predicted to truncate the C-terminal domain necessary to anchorage of EPCAM at the intercellular membrane. Consistently, immunohistochemistry of intestinal biopsies failed to detect the EPCAM protein at the intercellular membrane level. The c.498insC mutation was found on the background of a minimal common haplotype of 473kb suggesting a very old founder effect (5000-6000 yrs).

TAC3 and TACR3 defects cause hypothalamic congenital hypogonadotropic hypogonadism in humans.

CONTEXT: Missense loss-of-function mutations in TAC3 and TACR3, the genes encoding neurokinin B and its receptor NK3R, respectively, were recently discovered in kindreds with nonsyndromic normosmic congenital hypogonadotropic hypogonadism (CHH), thus identifying a fundamental role of this pathway in the human gonadotrope axis. OBJECTIVE: The objective of the study was to investigate the consequences on gonadotrope axis of TAC3 deletion and TACR3 truncation in adult patients with normosmic complete CHH. RESULTS: We identified three unrelated patients with the same homozygous substitution in the TAC3 intron 3 acceptor splicing site (c.209-1G>C) and three siblings who bore a homozygous mutation in the TACR3 intron 2 acceptor splicing site (c.738-1G>A). We demonstrated that these two mutations, respectively, deleted neurokinin B and truncated its receptor NK3R. We found in three patients with TAC3 mutation originating from Congo and Haiti a founding event in a more distant ancestor by means of haplotype analysis. We calculated that time to this common ancestor was approximately 21 generations. In several patients we observed a dissociation between the very low LH and normal or nearly normal FSH levels, this gonadotropin responding excessively to the GnRH challenge test. This particular hormonal profile, suggests the possibility of a specific neuroendocrine impairment in patients with alteration of neurokinin B signaling. Finally, in these patients, pulsatile GnRH administration normalized circulating sex steroids, LH release, and restored fertility in one subject. CONCLUSION: Our data demonstrate the hypothalamic origin of the gonadotropin deficiency in these genetic forms of normosmic CHH. Neurokinin B and NK3R therefore both play a crucial role in hypothalamic GnRH release in humans.

Involvement of the modifier gene of a human Mendelian disorder in a negative selection process.

BACKGROUND: Identification of modifier genes and characterization of their effects represent major challenges in human genetics. SAA1 is one of the few modifiers identified in humans: this gene influences the risk of renal amyloidosis (RA) in patients with familial Mediterranean fever (FMF), a Mendelian autoinflammatory disorder associated with mutations in MEFV. Indeed, the SAA1 alpha homozygous genotype and the p.Met694Val homozygous genotype at the MEFV locus are two main risk factors for RA. METHODOLOGY/PRINCIPAL FINDINGS: HERE, WE INVESTIGATED ARMENIAN FMF PATIENTS AND CONTROLS FROM TWO NEIGHBORING COUNTRIES: Armenia, where RA is frequent (24%), and Karabakh, where RA is rare (2.5%). Sequencing of MEFV revealed similar frequencies of p.Met694Val homozygotes in the two groups of patients. However, a major deficit of SAA1 alpha homozygotes was found among Karabakhian patients (4%) as compared to Armenian patients (24%) (p = 5.10(-5)). Most importantly, we observed deviations from Hardy-Weinberg equilibrium (HWE) in the two groups of patients, and unexpectedly, in opposite directions, whereas, in the two control populations, genotype distributions at this locus were similar and complied with (HWE). CONCLUSIONS/SIGNIFICANCE: The excess of SAA1alpha homozygotes among Armenian patients could be explained by the recruitment of patients with severe phenotypes. In contrast, a population-based study revealed that the deficit of alpha/alpha among Karabakhian patients would result from a negative selection against carriers of this genotype. This study, which provides new insights into the role of SAA1 in the pathophysiology of FMF, represents the first example of deviations from HWE and selection involving the modifier gene of a Mendelian disorder.

Permanent muscle weakness in McArdle disease.

McArdle disease is an autosomal recessive muscle glycogenosis. In the typical clinical presentation, only exercise-related symptoms are noted. Nevertheless, permanent weakness may occur, usually late in life. In this study we report on the clinical and genetic features of fixed muscle weakness in McArdle disease. Among the 80 McArdle patients being followed at the Institute of Myology of the Salpêtrière Hospital, 9 patients have permanent weakness. The diagnosis of McArdle disease was confirmed by muscle biopsy and genetic investigations. Two patterns of muscle weakness and wasting were noted: (1) proximal and symmetric in 5 patients; and (2) asymmetric, mimicking facioscapulohumeral dystrophy (FSHD) in 4 patients. Computerized tomography scan showed fatty infiltration in the shoulder and pelvic girdle muscles. There was no clear correlation between genotype and the severity of muscle weakness. Proximal muscle weakness appeared after the age of 40 years and affected 11% of subjects in our series of 80 McArdle patients. Among patients over 40 years of age, 37.5% had muscle weakness.

The inspection paradox and whole-genome analysis.

One of the major challenges of modern biology is distinguishing meaningful patterns from the random fluctuations of DNA sequences resulting from chromosome shuffling in each generation. A disease-causing mutation is more likely to be found in a large recombination interval. The paradoxical observation that causal genetic variants are more likely to be found in larger intervals is a consequence of sampling bias and is known as the inspection paradox. According to this paradox, the interval containing a fixed point (the causal gene variant) is around double the length of an interval not subject to this constraint, but this average doubling of length is attenuated or neutralized at the ends of chromosomes, where the distribution of interval sizes gradually returns to normal. This prediction is experimentally testable. The consequences of sampling biases for haplotype patterns are small in large studies of many families, but may be more marked when trying to counsel an individual family, because the doubling of the size of segments is only a large-number average, and the effect may be much larger for an unusual number of recombination events. The challenge of identifying a causal signature from haplotype patterns is illustrated by the problem of the proportion of X-linked mutations in pairs of affected brothers.

Population history and infrequent mutations: how old is a rare mutation? GUCY2D as a worked example.

The mosaic pattern of haplotypes observed around a single mutation results from one or several founder events. The difficulties involved in calculating the age of the variant are greatly reduced by assuming a single event, but this simplification may bias analysis of the genealogy of the mutation. However, if it is assumed that more than one founder event occurred, the number of genealogies is very large and the likelihood of every possible tree could not be realistically calculated. A multipoint approach is required, given the number of independent variables needed to describe a complex bifurcating genealogy. Starting from the observation that a limited number of parameters is needed for calculation of the simplest models of bifurcating genealogies, we show that the probability density of a two-ancestor model genealogy can be simply described as an algebraic function in a closed form, two coalescence times being calculated simultaneously without compromising accuracy. Implementation in a Bayesian framework is facilitated by the simplicity of the function, which describes the reciprocal relationship between the region of complete linkage disequilibrium and the branch length of the tree. We illustrate the use of haplotype information about allele-sharing decay around a mutation as a genetic clock, using data for two GUCY2D mutations in Mediterranean populations.

Origin of the prevalent SFTPB indel g.1549C > GAA (121ins2) mutation causing surfactant protein B (SP-B) deficiency.

The SFTPB gene indel g.1549C > GAA (121ins2) accounts for about 2/3 of the mutant alleles underlying complete surfactant protein B deficiency. It is unclear, however, whether its prevalence is due to recurrent mutation or a founder effect. The underlying mutational mechanism was therefore sought through the analysis of local DNA sequence complexity. A relatively complex two-step process was proposed: the first step involving slipped mispairing mediated by a direct repeat and generating an AGAA micro-insertion, the second step involving hairpin loop resolution resulting in a CA micro-deletion. The possibility of a founder effect was then assessed by typing 8 intragenic SNPs in 17 independent 121ins2 chromosomes from 10 probands, with parental non-121ins2 chromosomes serving as controls. The 121ins2 chromosomes were assigned to three discrete haplotypes, whilst control chromosomes were distributed between 10 of the 11 observed parental haplotypes. The 121ins2 mutation was in strong and significant linkage disequilibrium (LD) with the tightly linked marker g.1580T/C (|D'| = 1; P approximately 0.024), although only moderate LD was found with the rest of the locus (|D'| approximately 0.54; P approximately 0.136). Data on haplotype structure and the locus LD pattern, obtained from 81 independent Western-European chromosomes, were consistent with the three mutation-bearing haplotypes having originated from a common ancestor by recombination. Interestingly, all families harboring the 121ins2 indel had ancestors from a region of Northwestern Europe populated by Frankish/Saxon migration. Taken together, these data are consistent with the view that an indel mutation occurred on a relatively common SFTPB haplotype and now accounts for the majority of (and possibly all) extant 121ins2 chromosomes.

Variable hypomethylation of D4Z4 in facioscapulohumeral muscular dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) progressively affects the facial, shoulder, and upper arm muscles and is associated with contractions of the polymorphic D4Z4 repeat array in 4q35. Recently, we demonstrated that FSHD alleles are hypomethylated at D4Z4. To study potential relationships between D4Z4 hypomethylation and both residual repeat size and clinical severity, we compared the clinical severity score with D4Z4 methylation in unrelated FSHD patients. Correcting the clinical severity score for age at examination improves the parameter to define clinical severity and provides further support for hypomethylation of FSHD alleles. However, a linear relationship between repeat size and clinical severity of the disease cannot be established. Interestingly, FSHD can be separated in two clinical severity classes: patients with residual repeat sizes of 10 to 20 kb are severely affected and show pronounced D4Z4 hypomethylation. In contrast, patients with repeat sizes of 20 to 31kb show large interindividual variation in clinical severity and D4Z4 hypomethylation. Because the majority of familial FSHD cases are represented in this interval and considering the overt variation in clinical severity in these familial cases, it thus is imperative to develop comprehensive allele-specific assays monitoring total D4Z4 methylation to investigate whether interindividual variation in D4Z4 methylation can be translated into a prognostic factor for clinical severity.

Polymorphism of the D4Z4 locus associated with facioscapulohumeral muscular dystrophy 1A in Shanghai population.

OBJECTIVE: To investigate the D4Z4 repeats on chromosome 4q35 in normal individuals in Shanghai and analysis the polymorphism of the D4Z4 locus. METHODS: The length of D4Z4 repeats on chromosome 4q35 in 191 normal individuals in Shanghai was determined by pulsed-field gel electrophoresis and Southern blotting after double digestion with Eco RI and Bln I. The number of short D4Z4 repeats was counted after partial digestion with Kpn I. RESULTS: Among 191 normal individuals in Shanghai, seventeen showed the size of D4Z4 fragments ranged from 22 to 34 kb, i.e. 8.9% of individuals had fewer numbers of D4Z4 repeats. Of these 17 individuals, sixteen showed the short D4Z4 fragment on chromosome 4q35, and one low D4Z4 fragment was correlated to 4q35--> 10q26 translocation. CONCLUSION: The frequency of individuals having fewer numbers of D4Z4 repeats on chromosome 4q35 in Shanghai population is higher than that in Caucasian population although the short D4Z4 fragment on chromosome 4q35 is associated with facioscapulohumeral muscular dystrophy. These findings suggest that other factors may also contribute to facioscapulohumeral muscular dystrophy.

Mutation history of the roma/gypsies.

The 8-10 million European Roma/Gypsies are a founder population of common origins that has subsequently split into multiple socially divergent and geographically dispersed Gypsy groups. Unlike other founder populations, whose genealogy has been extensively documented, the demographic history of the Gypsies is not fully understood and, given the lack of written records, has to be inferred from current genetic data. In this study, we have used five disease loci harboring private Gypsy mutations to examine some missing historical parameters and current structure. We analyzed the frequency distribution of the five mutations in 832-1,363 unrelated controls, representing 14 Gypsy populations, and the diversification of chromosomal haplotypes in 501 members of affected families. Sharing of mutations and high carrier rates supported a strong founder effect, and the identity of the congenital myasthenia 1267delG mutation in Gypsy and Indian/Pakistani chromosomes provided the best evidence yet of the Indian origins of the Gypsies. However, dramatic differences in mutation frequencies and haplotype divergence and very limited haplotype sharing pointed to strong internal differentiation and characterized the Gypsies as a founder population comprising multiple subisolates. Using disease haplotype coalescence times at the different loci, we estimated that the entire Gypsy population was founded approximately 32-40 generations ago, with secondary and tertiary founder events occurring approximately 16-25 generations ago. The existence of multiple subisolates, with endogamy maintained to the present day, suggests a general approach to complex disorders in which initial gene mapping could be performed in large families from a single Gypsy group, whereas fine mapping would rely on the informed sampling of the divergent subisolates and searching for the shared genomic region that displays the strongest linkage disequilibrium with the disease.

Refined genetic mapping of autosomal recessive chronic distal spinal muscular atrophy to chromosome 11q13.3 and evidence of linkage disequilibrium in European families.

Chronic distal spinal muscular atrophy (Chronic DSMA, MIM (*)607088) is a rare autosomal recessive disorder characterized by a progressive motor weakness and muscular atrophy, predominating in the distal parts of the limbs. A form of Chronic DSMA gene has been previously mapped to chromosome 11q13 in the 10.3 cM interval defined by loci D11S1889 and D11S1321. By linkage analysis in 12 European Chronic DSMA families, we showed that a disease gene maps to chromosome 11q13.3 (Z(max)=6.66 at theta=0.00 at the DSM4 locus) and suggested that this condition is genetically homogeneous. Recombination events allowed us to reduce the genetic interval to a 2.6 cM region, telomeric to the IGHMBP2 gene, excluding this gene as the disease causing gene in Chronic DSMA. Moreover, partial linkage disequilibrium was found between three rare alleles at loci D11S1369, DSM4 and D11S4184 and the mutant chromosome in European patients. Analysis of the markers at these loci strongly suggests that most Chronic DSMA chromosomes are derived from a single ancestor. Refinement of the Chronic DSMA locus will hopefully allow to test candidate genes and lead to identification of the disease-causing mutations.

FOunder effect in patients with Unverricht-Lundborg disease on reunion island.

PURPOSE: Unverricht-Lundborg disease (ULD) is the most frequent form of progressive myoclonus epilepsy. ULD is caused mostly by a homozygous expansion of a dodecamer repeat in the cystatin B gene (CSTB) promoter. We present here a clinical and molecular study of 14 ULD patients originating from Reunion Island, a French island in the Indian Ocean. METHODS: These ULD patients were clinically evaluated, and the diagnosis of ULD was confirmed molecularly. We analyzed 12 microsatellites flanking CSTB and estimated the date of introduction of the ULD mutation on Reunion Island. RESULTS: These cases were clinically very similar, with the typical myoclonus syndrome associated with generalized tonic-clonic seizures, cerebellar involvement and, in some cases, mild mental deterioration. The mean age at onset was 9.6 years (range, 5-14 years), and the mean disease duration was 27 years (range, 5-47 years). The 14 patients harbored the typical ULD mutation, with variable degrees of expansion (mean of 56.3 repeats; range, 49-63). A founder effect was detected, with all but one of the Reunion ULD chromosomes displaying expansions belonging to the same haplotype, 1-1-1-2-6-4-3. We estimated the date of arrival of the most recent common ancestor (MRCA) of these patients on Reunion Island to the middle of the eighteenth century. CONCLUSIONS: These Reunion ULD patients displayed a homogeneous phenotype. Our molecular results are compatible with the instability of the repeat expansion and revealed a founder effect in Reunion ULD patients and the existence of a MRCA about 12 generations ago.