Biallelic variants were exclusively associated with UCMD in the COL6A1 cohort, whereas in the COL6A2 and COL6A3 cohorts, they were linked to different phenotypes, with BM being the most prevalent in the COL6A2 cohort (Figure 3). This evidence concerns the gene COL6A1 and Congenital muscular dystrophy, Ullrich type.