Achondrogenesis, type II and Hypochondrogenesis
Achondrogenesis, type II (ACG2; MIM 200610) and Hypochondrogenesis (MIM 200610) are lethal conditions caused by defects in COL2A1. Although they share phenotypic characteristics, ACG2 is considered more severe. Affected fetuses and infants have a large head, soft cranium, flat face, barrel shaped trunk, and short long bones. In ACG2 the entire spine and sacrum may not be ossified. Hydrops fetalis, prematurity and death at or shortly following birth is typical of both disorders. Achondrogenesis, type IB (ACG1B; MIM 600972) phenotypically resembles ACG2 but is caused by defects in the diastrophic sulfate transporter (DTDST). In ACG1B the head is normal or near normal in size and the thorax is thin.