A novel mild variant of osteogenesis imperfecta type I caused by a Gly1088Glu mutation in COL1A1

Osteogenesis imperfecta (OI), also known as brittle bone disease, characterized by multiplicative osteopsathyrosis, blue sclera, dentinogenesis imperfecta and mild audition, is a rare inherited connective tissue disease. There are seven types of OI, I to VII, among which type I-IV are relatively common and associated with type I collagen. Defects in type I collagen synthesis or structure are responsible for the majority of clinical OI cases since collagen is the major matrix protein of all connective tissues. Type I collagen consists of two pro-α1 chains and one pro-α2 chain, which are encoded by two genes, COL1A1 and COL1A2, respectively. The two subunits have a Gly-X-Y repeat domain, of which glycine is highly conserved in the majority of species. Point mutations on these sites appear to trigger OI. In the current study, a heterozygous mutation, c.3263G>A, p.Gly1088Glu, was identified in the Gly-X-Y domain of type I collagen in an affected individual with type I OI. A lethal phenotype with the p.Gly1088Ala mutation was observed at the same site as the current findings. This suggests that variant characteristics of the substitution for Gly may trigger a varying degree of OI from lethal to mild, even when the mutation occurs at the same site. It is hypothesized that the study may provide insight into the phenotype-genotype association and may assist, not only in the clinical diagnosis, but also in investigating the mechanism of collagen-associated diseases.