Molecular characterization of congenital myasthenic syndromes in Spain.

Congenital myasthenic syndromes (CMS) are a heterogeneous group of genetic disorders, all of which impair neuromuscular transmission. Epidemiological data and frequencies of gene mutations are scarce in the literature. Here we describe the molecular genetic and clinical findings of sixty-four genetically confirmed CMS patients from Spain. Thirty-six mutations in the CHRNE, RAPSN, COLQ, GFPT1, DOK7, CHRNG, GMPPB, CHAT, CHRNA1, and CHRNB1 genes were identified in our patients, with five of them not reported so far. These data provide an overview on the relative frequencies of the different CMS subtypes in a large Spanish population. CHRNE mutations are the most common cause of CMS in Spain, accounting for 27% of the total. The second most common are RAPSN mutations. We found a higher rate of GFPT1 mutations in comparison with other populations. Remarkably, several founder mutations made a large contribution to CMS in Spain: RAPSN c.264C > A (p.Asn88Lys), CHRNE c.130insG (Glu44Glyfs*3), CHRNE c.1353insG (p.Asn542Gluf*4), DOK7 c.1124_1127dup (p.Ala378Serfs*30), and particularly frequent in Spain in comparison with other populations, COLQ c.1289A > C (p.Tyr430Ser). Furthermore, we describe phenotypes and distinguishing clinical signs associated with the various CMS genes which might help to identify specific CMS subtypes to guide diagnosis and management.

Espectro mutacional de la distrofia muscular de Duchenne en España: estudio de 284 casos / Mutational spectrum of Duchenne muscular dystrophy in Spain: Study of 284 cases

Introducción: La distrofia muscular de Duchenne (DMD) es una enfermedad neuromuscular grave que afecta a uno de cada 3.500 varones nacidos y sigue un patrón de herencia ligada al cromosoma X. En esta enfermedad se observa una ausencia total de la distrofina, generalmente debida a mutaciones en el gen DMD, que altera la pauta de lectura y en torno al 80% de los casos son debidos a deleciones y duplicaciones de uno o más exones. Métodos: Se han revisado 284 casos de varones diagnosticados genéticamente de DMD entre los años 2007 y 2014. Estos pacientes provienen de 8 hospitales españoles de referencia que cubren la mayor parte del territorio español. Para la identificación de las mutaciones se realizaron las técnicas de reacción en cadena de la polimerasa multiplex, MLPA y secuenciación. Resultados: Los pacientes con DMD presentan en su mayoría grandes deleciones (46,1%) o grandes duplicaciones (19,7%) en el gen de la distrofina. El restante 34,2% corresponde al conjunto de mutaciones puntuales, destacando las sustituciones nucleotídicas tipo nonsense que aparecen en la mitad de los casos. Este estudio permitió identificar 23 nuevas mutaciones en DMD: 7 grandes deleciones y 16 mutaciones puntuales. Conclusiones: El algoritmo de diagnóstico genético aplicado por los centros participantes es el más adecuado para genotipificar a los pacientes con DMD. La especificidad genética de las distintas terapias en desarrollo pone de manifiesto la importancia de conocer la mutación de cada paciente, siendo un 38,7% de ellos susceptibles de participar en los ensayos clínicos actuales (AU)

Introduction: Duchenne muscular dystrophy (DMD) is a severe X-linked recessive neuromuscular disease that affects one in 3500 live-born males. The total absence of dystrophin observed in DMD patients is generally caused by mutations that disrupt the reading frame of the DMD gene, and about 80% of cases harbour deletions or duplications of one or more exons. Methods: We reviewed 284 cases of males with a genetic diagnosis of DMD between 2007 and 2014. These patients were selected from 8 Spanish reference hospitals representing most areas of Spain. Multiplex PCR, MLPA, and sequencing were performed to identify mutations. Results: Most of these DMD patients present large deletions (46.1%) or large duplications (19.7%) in the dystrophin gene. The remaining 34.2% correspond to point mutations, and half of these correspond to nonsense mutations. In this study we identified 23 new mutations in DMD: 7 large deletions and 16 point mutations. Conclusions: The algorithm for genetic diagnosis applied by the participating centres is the most appropriate for genotyping patients with DMD. The genetic specificity of different therapies currently being developed emphasises the importance of identifying the mutation appearing in each patient; 38.7% of the cases in this series are eligible to participate in current clinical trials (AU)

Mutational spectrum of Duchenne muscular dystrophy in Spain: Study of 284 cases. / Espectro mutacional de la distrofia muscular de Duchenne en España: estudio de 284 casos.

INTRODUCTION: Duchenne muscular dystrophy (DMD) is a severe X-linked recessive neuromuscular disease that affects one in 3500 live-born males. The total absence of dystrophin observed in DMD patients is generally caused by mutations that disrupt the reading frame of the DMD gene, and about 80% of cases harbour deletions or duplications of one or more exons. METHODS: We reviewed 284 cases of males with a genetic diagnosis of DMD between 2007 and 2014. These patients were selected from 8 Spanish reference hospitals representing most areas of Spain. Multiplex PCR, MLPA, and sequencing were performed to identify mutations. RESULTS: Most of these DMD patients present large deletions (46.1%) or large duplications (19.7%) in the dystrophin gene. The remaining 34.2% correspond to point mutations, and half of these correspond to nonsense mutations. In this study we identified 23 new mutations in DMD: 7 large deletions and 16 point mutations. CONCLUSIONS: The algorithm for genetic diagnosis applied by the participating centres is the most appropriate for genotyping patients with DMD. The genetic specificity of different therapies currently being developed emphasises the importance of identifying the mutation appearing in each patient; 38.7% of the cases in this series are eligible to participate in current clinical trials.

Isolated cardiomyopathy caused by a DMD nonsense mutation in somatic mosaicism: genetic normalization in skeletal muscle.

X-linked dilated cardiomyopathy is a pure cardiac dystrophinopathy phenotype mainly caused by DMD mutations that present a specific transcription effect in cardiac tissue. We report a 26-year-old male who presented with severe dilated cardiomyopathy and high creatine kinase. The patient did not complain of skeletal muscle weakness. A muscle biopsy showed mild dystrophic changes and a low proportion of dystrophin-negative fibres. A molecular study identified a nonsense DMD mutation (p.Arg2098X) in somatic mosaicism. The ratio of mutant versus normal allele in blood and skeletal muscle suggests selective pressure against mutant muscle cells, a process known as genetic normalization. We hypothesize that this process may have mitigated skeletal muscle symptoms in this patient. This is the second report of a DMD somatic mosaic with evidence of genetic normalization in muscle. Somatic DMD mutations should be considered in patients presenting with idiopathic dilated cardiomyopathy.

LMNA mutation in progeroid syndrome in association with strokes.

Hutchinson-Gilford progeria syndrome is a very rare but well-characterized genetic disorder that causes premature ageing. Clinical features affect growth, skeleton, body fat, skin, hair and the cardiovascular system. It is caused by mutations in LMNA gene, the most frequent being p.Gly608Gly (c.1824C > T) in exon 11. Here we present a four-year-old HGPS patient who presented several severe strokes and carried a heterozygous LMNA missense mutation in exon 2: p.Glu138Lys. This mutation is located far from the C-terminal region implicated in the posttranslational processing of prelamin A, but it lies within the rod domain of lamin A/C that represents a highly conserved domain specific to nuclear lamins. We hypothesize that this region could be involved in early and severe strokes in HGPS, such as those presented by our patient.

Abnormal expression of dysferlin in skeletal muscle and monocytes supports primary dysferlinopathy in patients with one mutated allele.

BACKGROUND: In some cases, a definitive confirmation of dysferlinopathy cannot be achieved by DNA test, because the mutation is detected in one allele only. PATIENTS AND METHODS: DYSFERLIN expression in skeletal muscle and peripheral blood monocytes (PBM) was studied by Western blot in two unrelated adult patients. The comparative C(T) method (ΔΔC(T) ) was used to calculate relative changes in dysferlin mRNA determined from real-time quantitative PCR experiments. The dysferlin gene was studied by direct sequencing of cDNA and genomic DNA and by Multiplex Ligation-dependent Probe Amplification (MLPA) analysis. RESULTS: A comparable severe reduction in dysferlin was demonstrated in both skeletal muscle and PBM. The expression of dysferlin mRNA was significantly reduced. A novel mutation in exon 47 (c.5289G>C) of the dysferlin gene in the heterozygous state, causing an amino acid change (p.Glu1763Asp), was detected in both patients. The MLPA analysis did not reveal any deletion or duplication. CONCLUSIONS: Dysferlin and/or dysferlin mRNA abnormalities are diagnostic for dysferlinopathy when mutational analysis detects a mutation in one allele only. Analysis of dysferlin mRNA can be helpful for distinguishing symptomatic heterozygotes from such patients.

A new phenotype of dysferlinopathy with congenital onset.

We report two patients with a new phenotype of dysferlinopathy presenting as congenital muscular disease. Both patients showed weakness in proximal lower limbs and neck flexor muscles at birth. The presence of normal CK levels during the first years should be noted. Initial MRI showed no abnormalities but short-time-inversion-recovery (STIR) sequences revealed a striking myoedema in gastrocnemius and hamstring muscles at the age of 5. Muscle biopsy showed mild dystrophic features and the absence of dysferlin. Dysferlin gene (DYSF) analysis revealed a p.Ala927LeufsX21 mutation in a homozygous state in both siblings. This new phenotype widens the clinical spectrum of dysferlin myopathies.

Symptomatic dysferlin gene mutation carriers: characterization of two cases.

OBJECTIVE: To describe two symptomatic dysferlin gene mutation carriers. METHODS: One patient had limb girdle weakness. His brother was diagnosed with limb girdle muscular dystrophy 2B with two mutations in the dysferlin gene (D625Y and E1734G). The second patient had distal weakness. He had two sons with Miyoshi myopathy with a homozygous mutation (G519R). We performed immunofluorescence (dystrophin, DAG proteins, dysferlin, caveolin-3), Western blot (dysferlin, caveolin-3, calpain-3), and real-time PCR (dysferlin) using skeletal muscle samples. We also studied dysferlin in peripheral blood monocytes (PBMs) by Western blot. RESULTS: In addition to the muscle weakness, both patients showed elevated creatine kinase and abnormal muscle MRI. They presented a mutation in only one allele after screening of the whole gene (skeletal muscle and monocyte mRNA and genomic DNA). A muscle biopsy specimen showed moderate dystrophic changes and patchy dysferlin expression in the sarcolemma. Western blot of both PBMs and skeletal muscle demonstrated a significant reduction in dysferlin. All the other proteins including caveolin-3 and calpain-3 were normal. Real-time PCR showed normal levels of dysferlin mRNA vs the patients' affected relatives. CONCLUSIONS: The diagnosis of symptomatic carriers of dysferlin mutations should be considered when a pathologic pattern of dysferlin protein is observed.

Dysferlin expression in monocytes: a source of mRNA for mutation analysis.

Dysferlin protein is expressed in peripheral blood monocytes. The genomic analysis of the DYSF gene has proved to be time consuming because it has 55 exons. We designed a mutational screening strategy based on cDNA from monocytes to find out whether the mutational analysis could be performed in mRNA from a source less invasive than the muscle biopsy. We studied 34 patients from 23 families diagnosed with dysferlinopathy. The diagnosis was based on clinical findings and on the absence of protein expression using either immunohistochemistry or Western blot of skeletal muscle and/or monocytes. We identified 28 different mutations, 13 of which were novel. The DYSF mutations in both alleles were found in 30 patients and only in one allele in four. The results were confirmed using genomic DNA in 26/34 patients. This is the first report to furnish evidence of reliable mutational analysis using monocytes cDNA and constitutes a good alternative to genomic DNA analysis.

[Muscular dystrophy due to a deficit of gamma-sarcoglycan. A report of three patients with the Delta-521t mutation]. / Distrofia muscular por déficit de gamma-sarcoglicano. Aportación de tres pacientes con la mutación Delta-521T.

INTRODUCTION: gamma-sarcoglicanopathies, also classified as limb girdle muscular dystrophy type 2C (LGMD2C) are a group of autosomal recessive muscular dystrophies due to mutations in 13q12 and subsequent g sarcoglican deficiency. The protein is one of the components of the dystrophin associated glycoprotein complex and is thought to impart structural integrity to the myofibre. The clinical course of the disease may be heterogeneous, ranging from severe forms with onset in the first decade and rapid progression resembling Progressive Duchenne muscular dystrophy (DMD) to milder forms with later onset and slower course. Cases hitherto reported in Spain corresponds to gypsie patients, homozygous for C283Y missense mutation. CASE REPORTS: Here, we report three new galician (Northwest Spain) patients (one male and one female sibling cases) with a severe DMD like muscular dystrophy homozygous for D 521T. In the first male familial case, initial diagnosis of DMD was made. On reevaluation fourteen years later, inmunohistochemical and molecular studies allowed for a definitive g sarcoglicanopathy diagnosis. CONCLUSIONS: Patients with a primary sarcoglycanopathy may be clinically indistinguishable from those with the primary dystrophinopathies. Probably, the diagnosis of LGMD are underestimated and a number of male patients diagnosed as DMD really corresponds to a recessive form o muscular dystrophy. Consequently, a definitive diagnosis rests on appropriate inmunohistochemical and molecular analysis, specially in those patients showing a normal pattern of dystrophin and/or suggestive for an autosomal recessive mode of inheritance.

Distrofia muscular por déficit de -sarcoglicano. Aportación de tres pacientes con la mutación Delta-521T / Muscular dystrophy due to a deficit of g-sarcoglycan. A report of three patients with the Delta-521t mutation

Introducción. Las Gamma-sarcoglicanopatías o distrofias de cinturas tipo 2C (LGMD2C) constituyen un grupo de distrofias musculares progresivas de herencia autosómica recesiva debidas a mutaciones en 13q12 y al déficit subsiguiente de Gamma-sarcoglicano, uno de los constituyentes del complejo de proteínas asociado a la distrofina (DAP) que contribuye de forma primordial a la integridad de la membrana muscular. Desde el punto de vista clínico, su curso es en general similar al de la distrofia muscular progresiva tipo Duchenne, si bien algunas mutaciones determinadas se han asociado a un fenotipo menos grave. Los casos descritos en España corresponden en su mayoría a la mutación C283Y, exclusiva de la raza gitana. Casos clínicos. Describimos tres nuevos casos de pacientes gallegos (dos hermanos, varón y mujer) afectos de g-sarcoglicanopatía con fenotipo DMD, homocigotos para la mutación Delta-521T. En el primero de los casos familiares (varón) se efectuó el diagnóstico inicial de DMD, que permitió una reevaluación 14 años más tarde del establecimiento del diagnóstico definitivo en base a los hallazgos inmunohistoquímicos y moleculares. Conclusiones. El patrón clínico e histopatológico de las sarcoglicanopatías primarias puede ser indistinguible del de la DMD, hecho que sugiere que un número no determinado de casos de DMD en varones corresponde en realidad a formas autosómico recesivas de distrofias de cinturas (LGMD). El diagnóstico definitivo, en todo caso, de distrofia muscular debe establecerse sobre bases inmunohistoquímicas y moleculares apropiadas, y este hecho es de especial relevancia en los casos de varones con fenotipo DMD y patrón normal de distrofina, y en los casos sugerentes de un patrón de herencia autosómico recesivo (AU)

[Early onset adhalinopathy (LGMD2D) mimicking congenital muscular dystrophy]. / Adhalinopatía primaria (LGMD2D) de inicio en los primeros meses de la vida que simula una distrofia muscular congénita.

INTRODUCTION: The recent discovery of the dystrophin-associated complex of glycoproteins led to the delineation of sarcoglycanopathies, a phenotypically similar to dystrophinopathies group of clinically heterogeneous and progressive muscular dystrophies. The objective of this paper is to report the clinical, biochemical, histological, immunohistochemical and molecular genetics characteristics observed in a case of adhalinopathy (alpha-sarcoglycanopathy or LGMD2D) presenting in early months of life and resembling congenital muscular dystrophy. CLINICAL CASE: An 12-year old school boy, the third son of a healthy, young, non consanguineous couple, presented at birth with bilateral cleft lip, cleft palate and mild hypotonia. At age 6 months it was believed he suffered from a benign form of congenital muscular dystrophy on the basis of clinical, biochemical, electrophysiological and histological findings. From 5 years onwards he had frequent falls and climbing stairs had become increasingly difficult. Also, a positive Gowers 'sign, mild calf hypertrophy, high serum creatine-phosphokinase level and myopathic electromyographic features were present; otherwise, cardiological evaluation and intelligence were normal. A repeated muscular biopsy at 10 years showed dystrophic features as well as selective deficiency of adhalin on immunostaining. DNA analysis demonstrated the patient being homozygote for a R77C mutation. Actually, a marked lumbar lordosis and waddling gait, an impossibility of climbing stairs and arising from the floor in addition to absent rotulian reflexes and mild Achilles retraction are present. CONCLUSIONS: LGMD2D may present in the first months of life mimicking congenital muscular dystrophy. It seems reasonable that biopsies of all new cases of muscular dystrophies be selectively immohistochemical analyzed, and when it is possible the diagnosis should be confirmed by DNA analysis.

Adhalinopatía primaria (LGMD2D) de inicio en los primeros mesesde la vida que simula una distrofia muscular congénita / Early onset adhalinopathy (LGMD2D) mimicking congenital muscular dystrophy

Introducción. El reciente descubrimiento del complejo de proteínas relacionadas con la distrofina ha permitido delimitar un grupo de distrofias musculares progresivas clínicamente heterogéneo, denominadas sarcoglicanopatías, y con un curso evolutivo semejante al de las distrofinopatías. El objetivo de este trabajo es presentar las características clínicas, bioquímicas, histológicas, inmunohistoquímicas y genético-moleculares de una niño con una adhalinopatía (alfa-sarcoglicanopatía o LGMD2D) de inicio en los primeros meses de la vida y que simulaba una distrofia muscular congénita. Caso clínico. Niño de 12 años, tercer hijo de padres jóvenes y no consanguíneos, que nació con labio leporino bilateral, fisura palatina completa y discreta hipotonía. A los 6 meses, en función de criterios clínicos, bioquímicos séricos, neurofisiológicos e histológicos, se estableció el diagnóstico presuntivo de distrofia muscular congénita de posible curso benigno. Ulteriormente, a partir de los 5 años, se aprecia de forma progresiva torpeza motora, caídas frecuentes, dificultad para subir escaleras, presencia de signo de Gowers y ligera pseudohipertrofia de ambos gemelos, persistencia del aumento de la creatina fosfocinasa sérica y del patrón miopático en la electromiografía, siendo normal su inteligencia y la exploración cardiológica. En una nueva biopsia muscular, realizada a los 10 años, persiste el patrón histológico compatible con distrofia muscular, y las técnicas inmunohistoquímicas demuestran una deficiencia selectiva en adhalina (alfa-sarcoglicano). El análisis del correspondiente gen confirma homocigosis para la mutación R77C. Actualmente, presenta una marcha de ánade en el límite máximo, acentuada lordosis lumbar, pseudohipertrofia de ambas pantorrillas, arreflexia rotuliana, ligera retracción aquílea, imposibilidad para subir escaleras e incorporarse del suelo y moderada afectación del cinturón escapular. Conclusiones. La presente observación sugiere que, de forma excepcional, la LGMD2D puede debutar clínicamente en los primeros meses de la vida y simular una distrofia muscular congénita, circunstancia que obliga, con fines diagnósticos, a realizar a nivel muscular y de forma secuencial los inmunomarcajes específicos y, posteriormente, dependiendo de sus resultados, el correspondiente estudio genético molecular (AU)

Distal anterior compartment myopathy: a dysferlin mutation causing a new muscular dystrophy phenotype.

We report a family with a new phenotype of autosomal recessive muscle dystrophy caused by a dysferlin mutation. The onset of the illness is distal, in the muscles of the anterior compartment group. The disease is rapidly progressive, leading to severe proximal weakness. Muscle biopsy showed moderate dystrophic changes with no vacuoles. Dysferlin immunostaining was negative. Gene analysis revealed a frameshift mutation in the exon 50 (delG5966) of the DYSF gene. This phenotype further demonstrates the clinical heterogeneity of the dysferlinopathies.

Control de calidad en el laboratorio de diagnóstico prenatal / Quality control in the prenatal diagnosis laboratory

No disponible

Homogeneous phenotype of the gypsy limb-girdle MD with the gamma-sarcoglycan C283Y mutation.

OBJECTIVE: To characterize the clinical phenotype of LGMD2C in gypsies. BACKGROUND: Limb-girdle muscular dystrophy (LGMD) in gypsies of Western Europe is caused by a homozygous C283Y mutation on the same haplotype, suggesting a founder effect. METHODS: We performed clinical, laboratory, and muscle imaging studies of 40 patients. RESULTS: Mean age at onset was 5.3 years. One half of the patients had loss of ambulation by the age of 12; 13% still could walk after age 16. Calf hypertrophy, scapular winging, macroglossia, and lumbar hyperlordosis were common. Girdle, trunk, and proximal limb flexor muscles had earlier and more severe involvement. Cardiomyopathy was not observed. Five patients in the third decade of life required mechanical ventilation. Scoliosis was common in the nonambulatory stage. CONCLUSIONS: LGMD2C in gypsy patients with C283Y mutation presents a rather homogeneous phenotype, characterized by an initial Duchenne-like progressive course followed by a more prolonged survival rate possibly due to the absence of early respiratory impairment and cardiac failure.

Novel mutations in the muscle chloride channel CLCN1 gene causing myotonia congenita in Spanish families.

Mutations in the muscular voltage-dependent chloride channel gene (CLCN1), located at 7q35, lead to recessive and dominant myotonia congenita. We report four novel mutations identified in this gene, after clinical, electromyographic, and genetic studies performed on 13 unrelated families. Two of the four mutations (2512insCTCA and A218T) were identified in families with Thomsen's disease, one (Q658X) in a family with Becker's disease, and the fourth (R669C) in a presumably sporadic patient with the Becker phenotype. Although identification of the mutations allows us to establish some genotype/phenotype correlations, this does not wholly account for the clinical heterogeneity and the inheritance patterns of the disease.

Calpainopathy-a survey of mutations and polymorphisms.

Limb-girdle muscular dystrophy type 2A (LGMD2A) is an autosomal recessive disorder characterized mainly by symmetrical and selective atrophy of the proximal limb muscles. It derives from defects in the human CAPN3 gene, which encodes the skeletal muscle-specific member of the calpain family. This report represents a compilation of the mutations and variants identified so far in this gene. To date, 97 distinct pathogenic calpain 3 mutations have been identified (4 nonsense mutations, 32 deletions/insertions, 8 splice-site mutations, and 53 missense mutations), 56 of which have not been described previously, together with 12 polymorphisms and 5 nonclassified variants. The mutations are distributed along the entire length of the CAPN3 gene. Thus far, most mutations identified represent private variants, although particular mutations have been found more frequently. Knowledge of the mutation spectrum occurring in the CAPN3 gene may contribute significantly to structure/function and pathogenesis studies. It may also help in the design of efficient mutation-screening strategies for calpainopathies.

[Alterations in functional proteins. Calpaine-3 deficiency]. / Alteraciones en las proteínas funcionales. Déficit de calpaína 3.

INTRODUCTION: Muscular dystrophies due to calpain deficiency are the first example of a muscular dystrophy due to the mutation of a gene codifying for a non-structural enzymatic protein of unknown function and substrate. DEVELOPMENT: More than 70 mutations have been described in the gene structure, localized to chromosome 15. Although the time course and topography is fairly homogeneous, correlation between the different mutations and the phenotype has still to be analyzed. The age of onset of symptoms is usually between 8 and 14, with no difference between the sexes. There is a slow but uniformly progressive course starting in the pelvis and extending to the shoulder and the distal musculature. Almost all patients are confined to a wheelchair twenty years after onset of the disease. There is no facial, oculomotor or bulbar involvement and gemellar pseudohypertrophy is rare. However, a winged scapula and marked lumbar hyperlordosis is universal. No cardiac or cognitive changes have been observed. Muscle CT shows a pattern of atrophy, mainly of the posterior and medial muscle compartments and of the posterosuperficial group of the legs, which varies depending on the time the disorder has been present. This condition is the commonest etiological group of the dystrophy syndromes, especially of those of late infancy or juvenile onset, in the open populations studied to date. Muscle biopsy, stained by all methods available, is essential to rule out other types of progressive dystrophies secondary to deficiencies of structural proteins.

Severe limb girdle muscular dystrophy in Spanish gypsies: further evidence for a founder mutation in the gamma-sarcoglycan gene.

Limb-girdle muscular dystrophy type 2C (LGMD2C) is an autosomal recessive muscular dystrophy with primary gamma-sarcoglycan deficiency, generally associated with a severe clinical course. gamma-sarcoglycan, a 35kDa dystrophin-associated protein, is encoded by a single gene on chromosome 13q12. Six different mutations have been described in that gene, and it has been proved they are the origin of the disease. One of these mutations (C283Y), a G-->A transition in codon 283, was recently and exclusively identified in Gypsy patients from different European countries. We report the study of 11 LGMD2C unrelated Gypsy families (nine Spanish and two Portugese). The muscle biopsies of these patients showed a drastically decreased immunostaining with alpha and gamma-sarcoglycan antibodies. All the patients were homozygous for C283Y missense mutation, and all affected chromosomes (patients and heterozygous relatives) carried the allele 5 (112 bp) of the intragenic microsatellite D13S232. Unexpectedly, this allele is most frequent in the Caucasian population but not in the normal Gypsy population. The clinical severity of all patients demonstrates that the C283Y missense mutation in a homozygous state causes a severe LGMD2C (DMD-like). The elevated number of families ascertained let us assume that LGMD2C is prevalent in the Gypsy population, and that all the families have inherited a founding mutation.