COL6A3 and congenital myopathy with cores: Exactly how defects in the collagen network impact muscle function is not clear, nevertheless patients bearing mutations in Collagen VI (COL6A1, COL6A2 and COL6A3) suffer from Ulrich and Bethlem myopathies (Bethlem and Wijngaarden, 1976) and exhibit muscle contractures involving elbows and ankles, a clinical sign that has been also described in patients suffering of congenital myopathies linked to recessive RYR1 mutations (Monnier et al., 2008; Klein et al., 2012).