COL5A1 and Ehlers-Danlos syndrome: Classical EDS is most often caused by heterozygous pathogenic variants in COL5A1, leading to haploinsufficiency and a quantitative reduction in α1(V), the alpha 1 chain of type V collagen (Ritelli et al., 2013; Schwarze et al., 2000; Symoens et al., 2012; Wenstrup et al., 2000).