COL1A1 and osteogenesis imperfecta: It ascribed the phenotypes of OI types I–IV solely to pathogenic variants in type I collagen genes, COL1A1 and COL1A2. This approach proposed that different classes of genomic variants in COL 1 genes alone (nonsense, splicing, deletion frameshift, missense, etc.)determine the full range of phenotypes from severe perinatal through mildly affected non-deforming types of OI.