Mutations in COL6A3 are described in UCMD for the first time and illustrate the wide spectrum of phenotypes which can be caused by collagen VI deficiency.
This study not only broadens the allelic spectrum of pathogenic COL6A3 variants in myopathy but also gives an additional support to Ullrich congenital muscular dystrophy and Bethlem myopathy clinical continuum.
We undertook two prenatal diagnoses for UCMD in a consanguineous family where the disease was consistent with linkage to the COL6A3 locus and immunolabelling of collagen VI in the proband's skeletal muscle was severely reduced.
Mutations in the COL6A1, COL6A2 (21 q22.3) and COL6A3 (2 q37) genes, encoding the alpha 1, alpha 2 and alpha 3 chains of collagen VI, respectively, have been recently identified as responsible for UCMD in a total of 9 families.
Skin abnormalities, including predisposition to keratosis pilaris and abnormal scarring, were described in Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM) patients carrying mutations in COL6A1, COL6A2, and COL6A3 genes, whereas COL6A5, previously designated as COL29A1, was linked to atopic dermatitis.
A molecular study, performed by Pan et al. at the Thomas Jefferson University, demonstrated in the first a known mutation of Bethlem myopathy in COL6A1 and in the second the first dominantly acting mutation in UCMD and the first in COL6A1, previously associated only to Bethlem myopathy, with benign course and dominant inheritance.
A heterozygous COL6A1 gene deletion, resulting in a mutant protein that exerts a dominant negative effect, has recently been described in a severely affected UCMD patient.
Dominant mutations in COL6A1, COL6A2, and COL6A3, the three genes encoding collagen type VI, a ubiquitous extracellular matrix protein, are associated with Bethlem myopathy (BM) and Ullrich scleroatonic muscular dystrophy.
In vivo, ColVI deficiency causes fragmentation of acetylcholine receptor (AChR) clusters, with abnormal expression of NMJ-enriched proteins and re-expression of fetal AChRγ subunit, both in Col6a1 null mice and in patients affected by Ullrich congenital muscular dystrophy (UCMD), the most severe form of ColVI-related myopathies.
Characterization of a rare case of Ullrich congenital muscular dystrophy due to truncating mutations within the COL6A1 gene C-terminal domain: a case report.
Here, for the first time, we report a genotype-phenotype correlation demonstrating that heterozygous glycine substitutions in the triple-helix domain of COL6A1 are dominant and responsible for a milder Ullrich scleroatonic muscular dystrophy phenotype, and that recessive mutations in COL6A1 correlate with more severe clinical and biochemical Ullrich scleroatonic muscular dystrophy phenotypes.
UCMD, a severe disorder characterized by congenital muscle weakness, proximal joint contractures and marked distal joint hyperextensibility, has been considered a recessive condition, and homozygous or compound heterozygous mutations have been defined in COL6A2 and COL6A3.
Skin abnormalities, including predisposition to keratosis pilaris and abnormal scarring, were described in Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM) patients carrying mutations in COL6A1, COL6A2, and COL6A3 genes, whereas COL6A5, previously designated as COL29A1, was linked to atopic dermatitis.
We report comparative morphological findings between a UCMD patient harboring a homozygous COL6A2 mutation and a patient with a typical UCMD phenotype in which mutations in COL6 genes were excluded.
Position of glycine substitutions in the triple helix of COL6A1, COL6A2, and COL6A3 is correlated with severity and mode of inheritance in collagen VI myopathies.
This model, where dominant mutations cause mild Bethlem myopathy and recessive mutations cause severe UCMD was recently challenged when a patient with UCMD was shown to have a heterozygous in-frame deletion in COL6A1.
Dominant mutations in COL6A1, COL6A2, and COL6A3, the three genes encoding collagen type VI, a ubiquitous extracellular matrix protein, are associated with Bethlem myopathy (BM) and Ullrich scleroatonic muscular dystrophy.