INHERITANCE: sporadic new autosomal dominant mutations

FREQUENCY: 1/35,000; the most common form of lethal neonatal dwarfism

CLINICAL: in utero hydrocephalus from cloverleaf (Kleeblattschadel) skull deformity; short limbs, long narrow trunk, marked midface hypoplasia;

RADIOGRAPHIC: platyspondyly, telephone receiver femora

PATHOLOGY: lack of organized cell physeal columns; "ossification tufts" of mineralization extend from subchondral bone

PROGNOSIS: death at or soon after birth from respiratory insufficiency