Primary adhalinopathy: a common cause of autosomal recessive muscular dystrophy of variable severity.

Marked deficiency of muscle adhalin, a 50 kDa sarcolemmal dystrophin-associated glycoprotein, has been reported in severe childhood autosomal recessive muscular dystrophy (SCARMD). This is a Duchenne-like disease affecting both males and females first described in Tunisian families. Adhalin deficiency has been found in SCARMD patients from North Africa Europe, Brazil, Japan and North America (SLR & KPC, unpublished data). The disease was initially linked to an unidentified gene on chromosome 13 in families from North Africa, and to the adhalin gene itself on chromosome 17q in one French family in which missense mutations were identified. Thus there are two kinds of myopathies with adhalin deficiency: one with a primary defect of adhalin (primary adhalinopathies), and one in which absence of adhalin is secondary to a separate gene defect on chromosome 13. We have examined the importance of primary adhalinopathies among myopathies with adhalin deficiency, and describe several additional mutations (null and missense) in the adhalin gene in 10 new families from Europe and North Africa. Disease severity varies in age of onset and rate of progression, and patients with null mutations are the most severely affected.

Deficiency of dystrophin-associated proteins in Duchenne muscular dystrophy patients lacking COOH-terminal domains of dystrophin.

Dystrophin, the protein product of the Duchenne muscular dystrophy (DMD) gene, is a cytoskeletal protein tightly associated with a large oligomeric complex of sarcolemmal glycoproteins including dystroglycan, which provides a linkage to the extracellular matrix component, laminin. In DMD, the absence of dystrophin leads to a drastic reduction in all of the dystrophin-associated proteins, causing the disruption of the linkage between the subsarcolemmal cytoskeleton and the extracellular matrix which, in turn, may render muscle cells susceptible to necrosis. The COOH-terminal domains (cysteine-rich and carboxyl-terminal) of dystrophin have been suggested to interact with the sarcolemmal glycoprotein complex. However, truncated dystrophin lacking these domains was reported to be localized to the sarcolemma in four DMD patients recently. Here we report that all of the dystrophin-associated proteins are drastically reduced in the sarcolemma of three DMD patients in whom dystrophin lacking the COOH-terminal domains was properly localized to the sarcolemma. Our results indicate that the COOH-terminal domains of dystrophin are required for the proper interaction of dystrophin with the dystrophin-associated proteins and also support our hypothesis that the loss of the dystrophin-associated proteins in the sarcolemma leads to severe muscular dystrophy even when truncated dystrophin is present in the subsarcolemmal cytoskeleton.

Are cysteine-rich and COOH-terminal domains of dystrophin critical for sarcolemmal localization?

It has been hypothesized that the tight localization of dystrophin at the muscle membrane is carried out by its cysteine-rich and/or carboxyl domains. We report the results of biochemical and immunocytochemical investigations of dystrophin in muscle from a 1-yr-old patient with a large deletion that removes the distal part of the dystrophin gene, thus spanning the exons coding for the cysteine-rich and the carboxy-terminal domains, and extends beyond the glycerol kinase and congenital adrenal hypoplasia genes. Immunological analysis of muscle dystrophin shows that the deletion results in the production of a truncated, but stable, polypeptide correctly localized at the sarcolemma. These data indicate that neither the cysteine-rich domain, nor the carboxyl domain, are necessary for the appearance of normal dystrophin sarcolemmal localization.

Illegitimate transcription. Application to the analysis of truncated transcripts of the dystrophin gene in nonmuscle cultured cells from Duchenne and Becker patients.

We have previously demonstrated that there is a low level of transcription of tissue-specific genes in every cell type. In this study, we have taken advantage of this phenomenon, called illegitimate transcription, to analyze the muscle-type dystrophin mRNA in easily accessible cells such as lymphoid cells, fibroblasts, and peripheral blood cells from Duchenne and Becker muscular dystrophies with known internal gene deletion. The results showed that, in the studied regions surrounding the deletions, processing of truncated transcripts is identical in specific (muscle tissue) and in nonspecific cells (lymphoid cells). In Becker cases with out-of-frame deletions, the already described alternatively spliced species found in muscle samples were also found in nonspecific cells. These results demonstrate that illegitimate transcripts are a bona fide version of tissue-specific mRNA, and that they represent a useful material to investigate the qualitative consequences of gene defects at the mRNA level.

A novel mutation in DAX1 causes delayed-onset adrenal insufficiency and incomplete hypogonadotropic hypogonadism.

Mutations in the DAX1 gene cause X-linked adrenal hypoplasia congenita (AHC) and hypogonadotropic hypogonadism (HHG). In affected boys, primary adrenal insufficiency occurs soon after birth or during early childhood; HHG is recognized at the expected time of puberty. In this report, we describe the novel phenotype of a man who presented with apparently isolated adrenal insufficiency at 28 years of age. Examination revealed partial pubertal development and undiagnosed incomplete HHG. Gonadotropin therapy did not improve his marked oligospermia, suggesting a concomitant primary testicular abnormality. Genomic analysis revealed a novel missense mutation, I439S, in DAX1. The mutant DAX-1 protein was studied for its ability to function as a transcriptional repressor of target genes. Consistent with the patient's mild clinical phenotype, the I439S mutation conferred intermediate levels of repressor activity of DAX-1 when compared with mutations associated with classic AHC. This unique case extends the clinical spectrum of AHC to include delayed-onset primary adrenal insufficiency in adulthood and milder forms of HHG. Furthermore, in accordance with findings in Ahch (Dax1) knockout mice, the clinical features in this patient suggest that DAX-1 function is required for spermatogenesis in humans, independent of its known effects on gonadotropin production.

Disease severity in dominant Emery Dreifuss is increased by mutations in both emerin and desmin proteins.

Individuals with the same genetic disorder often show remarkable differences in clinical severity, a finding generally attributed to the genetic background. We identified two patients with genetically proven Emery-Dreifuss muscular dystrophy (EDMD) who followed an unusual course and had uncommon clinicopathological findings. We hypothesized digenic inheritance and looked for additional molecular explanations. Mutations in additional separate genes were identified in both patients. The first patient was a member of a family with molecularly proven X-linked EDMD. However, the clinical features were unusually severe for this condition in the propositus: he presented at 2.5 years with severe proximal weakness and markedly elevated serum creatine kinase. Muscle weakness rapidly progressed, leading to loss of independent ambulation by the age of 12. In addition, the patient developed cardiac conduction system disease requiring pacing at the age of 11 and severe dilated cardiomyopathy in the early teens. Despite pacing, he had several syncopal episodes attributed to ventricular dysrhythmias. As these resemble the cardiac features of patients with the autosomal dominant variant of EDMD, we examined the lamin A/C gene, identifying a de-novo mutation in the propositus. The second patient had a cardioskeletal myopathy, similar to his mother who had died more than 20 years previously. Because of the dominant family history, a laminopathy was suspected and a mutation in exon 11 of the LMNA gene was identified. This mutation, however, was not present in his mother, but instead, surprisingly, was identified in his virtually asymptomatic father. Unusual accumulations of desmin found in the cardiac muscle of the propositus prompted us to examine the desmin gene in this patient, and in so doing, we identified a desmin mutation, in addition to the LMNA mutation in the propositus. These cases suggest that separate mutations in related proteins that are believed to interact, or that represent different parts of a presumed functional pathway, may synergistically contribute to disease severity in autosomal dominant EDMD. Furthermore, digenic inheritance may well contribute to the clinical severity of many other neuromuscular disorders.

Mutations in the muscle sodium channel gene (SCN4A) in 13 French families with hyperkalemic periodic paralysis and paramyotonia congenita: phenotype to genotype correlations and demonstration of the predominance of two mutations.

Hyperkalemic periodic paralysis (hyperPP), paramyotonia congenita (PC) and PC with myotonia permanens are closely related muscle disorders of genetic origin due to allelic mutations in the muscle sodium channel gene, SCN4A. Seven families of French origin with hyperPP were studied. Five of these had the Thr704Met mutation, but 2 families, genetically linked to SCN4A, failed to show any of the known mutations of SCN4A. Correlations between the phenotype and the genotype were made for patients with the Thr704Met mutation. All 12 patients over 30 years old with the Thr704Met mutation presented muscle weakness due to degeneration of muscle fibers in addition to periodic paralysis. Only approximately 12.5% of patients with the Thr704Met mutation presented with clinical myotonia and about 50% with hyperkalemia. One family with PC displayed the Gly1306Val mutation with a phenotype similar to the one already reported for this mutation. Five families with either PC or PC with myotonia permanens had the Thr1313Met mutation indicating that the severity of myotonia and its permanence were variable. Two mutations of SCN4A were found to be predominant in these 13 families: the Thr704Met and the Thr1313Met mutations. Only 2 families with the Thr704Met mutation and 3 families with the Thr1313Met shared the same SCN4A haplotype determined with intragenic dinucleotide repeats. Recurrent mutations of SCN4A may contribute to the predominance of these two mutations in the French population.

Linkage of X-linked myopathy with excessive autophagy (XMEA) to Xq28.

X-linked myopathy with excessive autophagy (XMEA, MIM 310440) is a rare inherited mild myopathy. We have used 32 polymorphic markers spanning the entire X chromosome to exclude most of the chromosome except the Xq28 region in a large XMEA family. Using three additional families for linkage analysis, we have obtained a significant two-point lod score with marker DXS1183 (Z = 2.69 at theta = 0). Multipoint linkage analysis confirmed the assignment of the disease locus with a maximal lod score of 2.74 obtained at recombination fraction zero. Linkage of XMEA to the Xq28 region is thus firmly established. In addition, we have ruled out the Emery-Dreifuss muscular dystrophy to be allelic with XMEA by direct sequencing of the emerin gene in three of our families.

Pseudo-metabolic presentation in a Duchenne muscular dystrophy symptomatic carrier with 'de novo' duplication of dystrophin gene.

We report a 6-year-old female patient presenting with a sudden and severe single episode of rhabdomyolysis in which screening for a metabolic disorder was negative. Four months after the episode a muscle biopsy was performed and showed a mild pattern of necrosis/regeneration. Upon immunofluorescence, a mosaic pattern of dystrophin deficiency was found, and in the dystrophin deficient muscle fibres, the four proteins of the sarcoglycan complex were also lacking. Genetic analysis showed a duplication of exons 3 to 17 on one X-chromosome of the proband, but not on the mother's X-chromosome. A clearly skewed X-inactivation (85% of the defective X being active) was found and is consistent with the patient being symptomatic. To our knowledge, a spontaneous rhabdomyolysis in a female Duchenne muscular dystrophy carrier has never been reported.

A point mutation in the glycerol kinase gene associated with a deletion in the dystrophin gene in a familial X-linked muscular dystrophy: non-contiguous gene syndrome involving Becker muscular dystrophy and glycerol kinase loci.

We report a family with an X-linked recessive muscular dystrophy characterised by exercise-induced myalgia, recurrent pigmenturia and mild proximal muscle involvement. Immunocytochemical and immunoblotting analysis in muscle, using the antibody directed against the rod domain of dystrophin, revealed a loss of immunoreactivity, but the immunolabelling using the antibodies directed against the COOH and NH2 domains of dystrophin were almost normal. The immunoreactions for alpha-sarcoglycan, gamma-sarcoglycan and beta-dystroglycan were normal. In the five male patients of this family with increased serum creatine kinase levels (from x8 to x50), mass spectrometry screening of the urine revealed a large increase in glycerol elimination which was quantified by enzymatic assay (from x14 to x39). An in-frame deletion of the dystrophin gene (exons 13-29) was found in the same five males and in three carrier females. All the deleted chromosomes also carried a missense mutation at nucleotide 947 of the Xp glycerol kinase (GK) gene resulting in a Thr to Met substitution at codon 278. These findings indicate that the two mutations cosegregate on the same chromosome in this family. This is the first reported case of two physically independent mutations, within the DMD and GK genes, which are contiguous but several hundred kilobases apart.

Early presentation of X-linked Emery-Dreifuss muscular dystrophy resembling limb-girdle muscular dystrophy.

Emery-Dreifuss muscular dystrophy is an X-linked neuromuscular disorder caused by defects in the STA gene on Xq28, which codes for a nuclear protein named emerin. Affected patients usually present in early adolescence with scapulo-peroneal muscle weakness and wasting, and contractures of the tendo Achilles, elbows and paraspinal muscles, resulting in spine rigidity. We present here a case of Emery-Dreifuss muscular dystrophy with an unusually severe, early presentation. He presented at 2.5 years with predominantly proximal weakness and mild equinovarus deformity of the right foot. Serum creatine kinase activity was elevated (1994 IU/I) and a muscle biopsy at the age of 4 years showed marked dystrophic abnormalities. Normal expression of dystrophin, and no detectable deletion in the corresponding gene, excluded a diagnosis of Duchenne muscular dystrophy. Similarly, normal expression of alpha-sarcoglycan made a limb-girdle muscular dystrophy caused by a defect in a sarcoglycan unlikely. Several years later, examination of the proband's maternal cousin, aged 14 years, suggested Emery-Dreifuss muscular dystrophy. This was confirmed in both affected boys by the absence of emerin in muscle and leucocytes, and identification of a mutation in exon 4 of the STA gene. Carrier status in both mothers was also confirmed by mutational and protein analysis. Emery-Dreifuss muscular dystrophy should therefore be considered in the differential diagnosis of cases of early onset muscular dystrophy, even in the absence of the typical clinical features.

Additional case of female monozygotic twins discordant for the clinical manifestations of Duchenne muscular dystrophy due to opposite X-chromosome inactivation.

A pair of female monozygotic (MZ) twins, heterozygous carriers for a deletion in the DMD gene and discordant for the clinical manifestations of Duchenne muscular dystrophy, were analyzed by molecular studies, in situ hybridization, and methylation pattern of X chromosomes to search for opposite X inactivation as an explanation of their clinical discordance. Results in lymphocytes and skin fibroblast cell lines suggest a partial mirror inactivation with the normal X chromosome preferentially active in the unaffected twin, and the maternal deleted X chromosome preferentially active in the affected twin. A review shows that MZ female twins discordant for X-linked diseases are not uncommon. Twinning and X inactivation may be interrelated and could explain the female twins discordant for X-linked traits.

Novel recurrent nonsense mutation causing neurofibromatosis type 1 (NF1) in a family segregating both NF1 and Noonan syndrome.

Neurofibromatosis type 1 (NF1), a genetic disorder with neuroectodermal involvement, demonstrates phenotypic overlap in some patients with Noonan syndrome (NS), ultimately resulting in the so-called neurofibromatosis-Noonan syndrome (NF-NS). A strong association of the two phenotypic traits was recently illustrated by a four-generation family, although NF1 and NS were eventually demonstrated to segregate independently on the basis of polymorphic DNA markers [Bahuau et al., 1996: Am J Med Genet 66:347-355]. Identification of the causal NF1 mutation seemed a prerequisite to further dissecting this singular familial association. Using the protein truncation assay, a nonsense mutation (C2446T-->R816X) of the neurofibromin gene was evidenced. This mutation occurred on a CpG dinucleotide within exon 16 and 5' to the GAP domain-specifying region of the gene. R816X creates a recognition site for endonuclease HphI, absent in 2 individuals with NS only. Screening 184 unrelated NF1 patients, three novel occurrences of the mutation were found in individuals diagnosed with classical NF1. Based on the assumption of genotype-phenotype correlation in these individuals, clinical and molecular analyses of this four-generation family demonstrated that the NF-NS phenotype was additive, being the result of both classical NF1 and NS. This particular observation also suggests the presence of an NS locus on 17q, which might be of interest for further linkage studies.

[Symptomatic carriers of dystrophinopathy with chromosome X inactivation bias]. / Les conductrices symptomatiques pour les dystrophinopathies avec biais d'inactivation du chromosome X.

Several studies have recently highlighted the fact that the clinical involvement in females carrying a mutation in the dystrophin gene could be more frequent than usually thought, suggesting the need of a careful cardiac follow-up. Except for the classical chromosomal rearrangements, it was shown that a bias in the X chromosome inactivation process could be found in some affected females. We report two families illustrating different situations. The propositus of the first family, aged 32, presented with a proximal muscular weakness, increasing for three years, as well as elevated muscular enzymes in blood. Her brother suffered from classical Duchenne muscular dystrophy. Her mother was more severely affected, whereas her sister remained asymptomatic. A duplication of exons 3 to 7 of the dystrophin gene was found in all four patients. The affected carrier from the second family was a sporadic case. She has been suffering from proximal muscular weakness for six years. Muscle biopsy showed a mosaic pattern of the immunostaining using specific antidystrophin antibodies. A stop mutation was found in exon 52. Her ten year-old daughter, carrying the mutation, was asymptomatic. In both families, the inactivation profiles were in accordance with the clinical presentation. We discuss the different mechanisms that may lead to the inactivation bias in these patients, as well as the advantage and limits of using the X chromosome inactivation test as a tool for diagnosis and prognosis purpose in symptomatic carriers for dystrophinopathies.

[Molecular pathology of Duchenne and Becker muscular dystrophy]. / Pathologie moléculaire des dystrophies musculaires de Duchenne et de Becker.

Duchenne and Becker muscular dystrophies (DMD and BMD) are two allelic recessive X-linked disorders. Molecular deletions of various regions of the dystrophin gene are the main mutations detected in DMD and BMD patients. Molecular study of DMD and BMD DNA are instrumental to understand the pathological molecular mechanisms and the function of the protein. We describe here dystrophin and its interaction with a glycoprotein complex and we then focus on two particular patients with partial deletions of the dystrophin gene: 1) a typical Becker patient, who shows an intragenic deletion disrupting the reading frame. We describe in this case alternative splicings restoring the reading frame, which might explain the mild clinical phenotype of this patient, 2) a deletion of the distal part of the DMD gene coding for the carboxyterminal domain of the dystrophin in a young patient. The normal localization of dystrophin at the inner face of the plasma membrane in the muscle of this patient suggests that the last domain of this protein is not sufficient to anchor dystrophin at the membrane.

Sporadic lower limb hypertrophy and exercise induced myalgia in a woman with dystrophin gene deletion.

A 25 year old woman, without family history of muscular dystrophy, had had an isolated lower limb hypertrophy since infancy and later experienced exercise-induced myalgia. Genomic DNA analysis showed a deletion of exons 45 to 52 of the dystrophin gene. Uncommon phenotypes of dystrophinopathies and consequences in genetic counselling in women are emphasised.

Analysis of molecular deletions with cDNA probes in patients with Duchenne and Becker muscular dystrophies.

In the course of a systematic survey of DMD and BMD patients with intronic probes and with cDNA probes covering three-fourths of the coding sequence, 45 molecular deletions within the DMD gene were investigated. Forty-two percent of the breakpoints were located in the intronic sequence containing probe P20, whereas the other deletions were widespread around the more proximal part of the gene. Most of the BMD deletions were in the P20 region. Pulsed field gel electrophoresis was used to determine the size of some deletions and allowed us to estimate the physical distance between the intronic probes JBir and P20. The reading frame was checked in 11 cases with proximal deletions and found to be disrupted in 6 of 7 DMD patients, in 1 intermediate case, and, unexpectedly, in 3 BMD patients.

[Metabolism of monocarbons and trisomy 21: sensitivity to methotrexate]. / Métabolisme des monocarbones et trisomie 21: sensibilité au méthotrexate.

A diminution of the mitotic index, proportionnal to the square of the dose of methotrexate, was observed in lymphocyte cultures. Six trisomy 21 patients were twice as sensitive as six controls. This highly significant result confirms the hypothesis of a disturbance of monocarbons' metabolism in trisomy 21.

Mild deficiency of dystrophin-associated proteins in Becker muscular dystrophy patients having in-frame deletions in the rod domain of dystrophin.

The dystrophin-glycoprotein complex spans the sarcolemma to provide a linkage between the subsarcolemmal cytoskeleton and the extracellular matrix in skeletal muscle. In Duchenne muscular dystrophy (DMD), the absence of dystrophin leads to a drastic reduction in all of the dystrophin-associated proteins in the sarcolemma, thus causing the disruption of the dystrophin-glycoprotein complex and the loss of the linkage to the extracellular matrix. The resulting sarcolemmal instability is presumed to render muscle fibers susceptible to necrosis. In the present study, we investigated the status of the dystrophin-associated proteins in the skeletal muscle from patients with Becker muscular dystrophy (BMD), a milder allelic form of DMD. BMD patients having in-frame deletions in the rod domain of dystrophin showed a mild to moderate reduction in all of the dystrophin-associated proteins in the sarcolemma, but this reduction was not as severe as that in DMD patients. The reduction of the immunostaining for the dystrophin-associated proteins showed a good correlation with that for dystrophin in both intensity and distribution. Our results indicate that (1) the abnormality of the sarcolemmal glycoprotein complex, which is similar to but milder than that in DMD patients, also exists in these BMD patients and (2) the rod domain of dystrophin is not crucial for the interaction with the dystrophin-associated proteins.

Effect of dystrophin gene deletions on mRNA levels and processing in Duchenne and Becker muscular dystrophies.

Muscle dystrophin mRNAs from Duchenne (DMD) and Becker (BMD) patients with internal deletion of the DMD gene were quantitated and sequenced. In all cases (eight DMD and three BMD), truncated mature transcripts were found, and their amount was correlated to the clinical phenotype and to the reading frame. We focused on four cases that were apparently not in agreement with the reading frame rule. In two DMD cases, slightly reduced amounts of in-frame truncated mRNA are present but no dystrophin is detected, suggesting impaired translation and/or instability of the protein. In two BMD patients with out-of-frame deletions, the presence of minor in-frame alternatively spliced mRNA species is congruent with the observed truncated dystrophin and the mild phenotype.