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A prenatal ultrasound reveals severe limb shortening, a narrow chest, and macrocephaly with a cloverleaf skull. Polyhydramnios is present. The pregnancy is complicated by hydrops.
AD (de novo); FGFR3 (different variants than achondroplasia)
- Type I: curved femurs ("telephone receiver")
- Type II: straight femurs, cloverleaf skull
- Lethal skeletal dysplasia (most common lethal)
- Severe limb shortening
- Narrow, bell-shaped chest → pulmonary hypoplasia
- Macrocephaly ± cloverleaf skull (type II)
- Platyspondyly (flattened vertebrae)
- Usually die in neonatal period (respiratory insufficiency)
- Typically detected on prenatal ultrasound: severe micromelia (short-limbed short stature), narrow thorax, macrocephaly, polyhydramnios, curved ("telephone receiver") femurs in type I, cloverleaf skull in type II
- Postnatal radiographs: severe platyspondyly, short ribs, short tubular bones
- Confirmatory FGFR3 molecular testing (variants distinct from achondroplasia)
- Differentiate from other lethal skeletal dysplasias (e.g. achondrogenesis, osteogenesis imperfecta type II)
- Generally lethal in the perinatal period; care centers on goals-of-care discussion and palliative/comfort support
- Prenatal counseling regarding prognosis and delivery planning
- Recurrence risk counseling: most cases de novo, with low recurrence but a small risk from gonadal mosaicism