Evidence for locus heterogeneity in the Bethlem myopathy and linkage to 2q37 (original) (raw)
Related papers
1998
The Bethlem myopathy is a rare autosomal dominant proximal myopathy characterized by early childhood onset and joint contractures. Evidence for linkage and genetic heterogeneity has been established, with the majority of families linked to 21q22.3 and one large family linked to 2q37, implicating the three type VI collagen subunit genes, COL6A1 (chromosome 21), COL6A2 (chromosome 21) and COL6A3 (chromosome 2) as candidate genes. Mutations of the invariant glycine residues in the triple-helical domain-coding region of COL6A1 and COL6A2 have been reported previously in the chromosome 21-linked families. We report here the identification of a G→A mutation in the N-terminal globular domain-coding region of COL6A3 in a large American pedigree (19 affected, 12 unaffected), leading to the substitution of glycine by glutamic acid in the N2 motif, which is homologous to the type A domains of the von Willebrand factor. This mutation segregated to all affected family members, to no unaffected family members, and was not identified in 338 unrelated Caucasian control chromosomes. Thus mutations in either the triple-helical domain or the globular domain of type VI collagen appear to cause Bethlem myopathy.
Human Molecular Genetics, 1998
The Bethlem myopathy is a rare autosomal dominant proximal myopathy characterized by early childhood onset and joint contractures. Evidence for linkage and genetic heterogeneity has been established, with the majority of families linked to 21q22.3 and one large family linked to 2q37, implicating the three type VI collagen subunit genes, COL6A1 (chromosome 21), COL6A2 (chromosome 21) and COL6A3 (chromosome 2) as candidate genes. Mutations of the invariant glycine residues in the triple-helical domain-coding region of COL6A1 and COL6A2 have been reported previously in the chromosome 21-linked families. We report here the identification of a G→A mutation in the N-terminal globular domain-coding region of COL6A3 in a large American pedigree (19 affected, 12 unaffected), leading to the substitution of glycine by glutamic acid in the N2 motif, which is homologous to the type A domains of the von Willebrand factor. This mutation segregated to all affected family members, to no unaffected family members, and was not identified in 338 unrelated Caucasian control chromosomes. Thus mutations in either the triple-helical domain or the globular domain of type VI collagen appear to cause Bethlem myopathy.
Autosomal recessive inheritance of classic Bethlem myopathy
Neuromuscular Disorders, 2009
Mutations in the collagen VI genes (COL6A1, COL6A2, and COL6A3) result in Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) or phenotypes intermediate between UCMD and BM. While UCMD can be caused by either recessively or dominantly acting mutations, BM has thus far been described as an exclusively autosomal dominant condition. We report two adult siblings with classic Bethlem myopathy who are compound heterozygous for a single nucleotide deletion (exon 23; c.1770delG), leading to in-frame skipping of exon 23 on the maternal allele, and a missense mutation p.R830W in exon 28 on the paternal allele. The parents are carriers of the respective mutations and are clinically unaffected. The exon skipping mutation in exon 23 results in a chain incapable of heterotrimeric assembly, while p.R830W likely ameliorates the phenotype into the Bethlem range. Thus, autosomal recessive inheritance can also underlie Bethlem myopathy, supporting the notion that UCMD and BM are part of a common clinical and genetic spectrum.
Biochemical and Biophysical Research Communications, 1999
Bethlem myopathy is a mild neuromuscular disorder with proximal muscular weakness and early flexion contractures. It is an autosomal dominant disease due to mutations in type VI collagen genes. We found a T3 C substitution at the ؉2 position of COL6A1 intron 14 in a family, leading to skipping of exon 14 and an in-frame deletion of 18 amino acids in the triplehelical domain of the ␣1(VI) collagen chain. The deletion included a cysteine residue believed to be involved in the assembly of type VI collagen dimers intracellularly, prior to the protein secretion. Analysis of the affected fibroblasts showed that the shortened ␣1(VI) collagen chains were synthesized but not secreted by the cells and that the amount of type VI collagen microfibrils deposited by the cells was reduced. The results suggest that the clinical phenotype is due to a reduction in the level of type VI collagen in the extracellular matrix.
Journal of Neuromuscular Diseases
A family of five male siblings (three survivors at 48, 53 and 58 years old; two deceased at 8 months old and 2.5 years old) demonstrating significant phenotypic variability ranging from intermediate to the myosclerotic like Bethlem myopathy is presented. Whole-exome sequencing (WES) identified a new homozygous missense mutation chr21:47402679 T > C in the canonical splice donor site of the second intron (c.227 + 2T>C) in the COL6A1 gene. mRNA analysis confirmed skipping of exon 2 encoding 925 amino-acids in 94–95% of resulting transcripts. Three sibs presented with intermediate phenotype of collagen VI-related dystrophies (48, 53 and 2.5 years old) while the fourth sibling (58 years old) was classified as Bethlem myopathy with spine rigidity. The two older siblings with the moderate progressive phenotype (48 and 53 years old) lost their ability to maintain a vertical posture caused by pronounced contractures of large joints, but continued to ambulate throughout life on fully b...
A spectrum of dominant collagen VI mutations in Bethlem myopathy
Matrix Biology, 2006
lymphocytes. Surviving subsets of Tg and KO mice likewise presented an altered lymphocyte profile in marrows and lymphatics throughout life. Moreover, all collagen X mice displayed altered serum and growth plate cytokine expression by ELISA, RT-PCR, and protein array. We propose a cytokine metabolism imbalance, linked to an impaired HC matrix, as a cause of hematopoietic defects in the collagen X mice. (DK057904 to OJ).
Journal of Clinical Neuromuscular Disease, 2021
Collagen VI-related myopathies are caused by mutations of COL6A1, COL6A2, and COL6A3 and present with a wide phenotypic spectrum ranging from severe Ulrich congenital muscular dystrophy to mild Bethlem myopathy. Here, we report a consanguineous Kurdish family with 3 siblings affected by autosomal-recessive Bethlem myopathy caused by compound heterozygous mutations of COL6A3. We found the previously described missense mutation c.7447A > G/p.(Lys2483Glu) and a novel large deletion encompassing the exon 1-39 of the COL6A3 gene. Apart from the classical clinical symptoms, all patients had keratoconus, which expands the phenotype of the collagen VI-related myopathies.
Bethlem myopathy: long-term follow-up identifies COL6 mutations predicting severe clinical evolution
Journal of Neurology, Neurosurgery & Psychiatry, 2014
Objective Mutations in one of the 3 genes encoding collagen VI (COLVI) are responsible for a group of heterogeneous phenotypes of which Bethlem myopathy (BM) represents the milder end of the spectrum. Genotype-phenotype correlations and long-term followup description in BM remain scarce. Methods We retrospectively evaluated the long-term clinical evolution, and genotype-phenotype correlations in 35 genetically identified BM patients (23 index cases). Results Nineteen patients showed a typical clinical picture with contractures, proximal weakness and slow disease progression while 11 presented a more severe evolution. Five patients showed an atypical presentation, namely a limb girdle muscle weakness in 2 and a congenital myopathy pattern with either no contractures, or only limited to ankles, in 3 of them. Pathogenic COL6A1-3 mutations were mostly missense or in frame exon-skipping resulting in substitutions or deletions. Twenty one different mutations were identified including 12novel ones. The mode of inheritance was, autosomal dominant in 83% of the index patients (including 17% (N=4) with a de novo mutation), recessive in 13%, and undetermined in one patient. Skipping of exon 14 of COL6A1 was found in 35% of index cases and was mostly associated with a severe clinical evolution. Missense mutations were detected in 39% of index cases and associated with milder forms of the disease. Conclusions Long-term follow-up identified important phenotypic variability in this cohort of 35 BM patients. However, worsening of the functional disability appeared typically after the age of 40 in 47% of our patients, and was frequently associated with COL6A1 exon 14 skipping.