Mutations in the COL12A1 gene have been described in a milder Bethlem-like myopathy in 6 patients from 3 families (dominant missense), and in a severe congenital form with failure to attain ambulation in 2 patients in a single pedigree (recessive loss-of-function). The authors describe an 8-year old girl of Polish origin who presented with profound hypotonia and joint hyperlaxity at birth after a pregnancy complicated by oligohydramnios and intrauterine growth retardation. They identified a novel, potentially pathogenic heterozygous missense COL12A1 c.8329G>C (p.Gly2777Arg) variant using a targeted sequencing panel. Patient fibroblast studies confirmed intracellular retention of the COL12A1 protein, consistent with a dominant-negative mutation.
