COL1A1 and hypochondroplasia: Overall, the most common genes in which molecular diagnoses were identified included: COL2A1 (n = 36) associated with type II collagenopathies (MIM 120140); FGFR3 (n = 24) associated with achondroplasia, thanatophoric dysplasia, hypochondroplasia, and other conditions such as FGFR-related craniosynostoses (MIM 134934); and COL1A1 (n = 13) or COL1A2 (n = 10) associated with osteogenesis imperfecta (OI; MIM 120150 and 120160, respectively).