Two closely spaced missense COL3A1 variants in cis cause vascular Ehlers‐Danlos syndrome in one large Chinese family

Vascular Ehlers‐Danlos syndrome (vEDS) is a rare and severe hereditary connective tissue disease arising from a mutation in the type III collagen alpha I chain (COL3A1) gene, with a poor prognosis due to exceptional vascular ruptures and premature death. Herein, starting from a 36‐year‐old Chinese male patient with a complaint of upper abdominal pain, we collected clinical data of and performed a genetic analysis of a total of 20 family members. We identified two closely spaced COL3A1 missense variants in cis, p.Leu734Phe (c.2199_2200TC>AT) and p.Gly741Ser (c.2221G>A), as the cause of vEDS in this family. p.Gly741Ser, a glycine substitution mutation, has been previously reported, whereas p.Leu734Phe, a non‐glycine substitution mutation, is novel. We analysed their independent and combined effects on the COL3A1 level in transfected skin fibroblast cells by means of Western blotting. We found that both variants independently led to a reduced COL3A1 level and, when combined, led to an even more reduced COL3A1 level compared to the wild type. Thus, each missense variant can be independently classified as a pathogenic variant, albeit with a synergetic effect when occurring together. Moreover, our genetic findings provide an explanation for four previous sudden deaths and identified two high‐risk carriers in the family.