COL6A1 and Ullrich congenital muscular dystrophy: Among the ten families with bi-allelic variants, in eight the variants were in COL6A2, while the other two each had variants in COL6A1, or in COL6A3. Six of these ten families had variants producing a premature termination codon or causing aberrant splicing, which leads to in-frame exon skipping in both alleles, and all had UCMD phenotypes.