Caused by mutation of the fibroblast growth factor receptor 3 gene, which is located on the short arm of chromosome 4. Is characterized by severe shortening of the ribs, restricted lung volume, and severe respiratory distress that leads to death within a few hours of birth
Type I: characterized by marked underdevelopment of the entire skeleton, short-curve long bones, and metaphyseal flaring (telephone receiver-like appearance). The pelvic bones are noticeably underdeveloped, and the acetabular roof is flat. The vertebral bodies also are very flat and underdeveloped. Cloverleaf skull may or may not be present.
Type II: long bones are not as short as in type I, and they are not bent or bowed. The metaphyses are flared and cupped. The vertebral bodies are flat but not as severely as is in type I TD. Almost all fetuses with type II TD have severe cloverleaf skull.
AJR 2009; 192: 48–51