Landscape Analysis of COL6A1, COL6A2, and COL6A3 Pathogenic Variants in a Large Italian Cohort Presenting with Collagen VI-Related Myopathies: A Nationwide Report

Collagen VI is an extracellular matrix component encoded by COL6A1, COL6A2 and COL6A3 genes. Causative variants in these genes are associated with the following collagen VI-related myopathies: severe Ullrich congenital muscular dystrophy (UCMD), milder Bethlem myopathy (BM) and intermediate phenotypes (INT). We report the mutation landscape of COL6A genes in 138 Italian patients affected with a collagen VI-related phenotype. The patient cohort included 44 (32%) UCMD, 9 (7%) INT, 61 (44%) BM and 21 (15%) INT/BM patients; 3 patients (2%) with a myosclerosis myopathy (MM) phenotype were also considered. We identified 104 different variants: 26 in COL6A1 (25%), 52 in COL6A2 (50%) and 26 in COL6A3 (25%). The variant spectrum includes missense, splicing, small indel, frameshifting and nonsense variants. Glycine substitutions in the triple helical domain of the collagen VI protein are the commonest variants and occur in all phenotypes. Our genetic profiling disclosed a unique mutation scenario and phenotypic association of the COL6A2 gene with respect to COL6A1 and COL6A3, which may be related to a different evolutive history. Landscape mutation analysis of variants occurring in ultrarare conditions, such as collagen VI-related myopathies, is crucial to better understand the variations’ profile and to gain insight into fundamental knowledge about gene structure and its evolutive origin.