Nail-patella syndrome, also known as Fong disease or osteo-onychodysostosis, is a rare autosomal dominant condition which results from symmetrical mesodermal and ectodermal abnormalities.
Clinically, the key feature is absent/hypoplastic nails from birth. Individuals may have flexion contractures and recurrent knee dislocations.
- renal dysfunction 5
The underlying genetic defect is caused by loss-of-function mutations in the transcription factor LMX1B on chromosome 9 5-6.
Diagnostic radiographic findings include:
- absent/hypoplastic patellae (with a tendency to recurrent dislocation)
- hypoplasia of the radial head or capitellum (leading to subluxation/dislocation)
- bilateral posterior iliac horns ("Fong's prongs")
- protuberant anterior iliac spines
The bilateral posterior iliac horns, due to exostoses arising from the posterior aspect of the iliac bones, are present in as many as 80% of patients; this finding is considered pathognomonic for the syndrome. The horns may be capped by an epiphysis. Other features include:
- genu valgum deformity
- flared iliac crests
- open angle glaucoma 6
- prominent tibial tuberosities
- short 5th metacarpal
- renal osteodystrophy
For absent patella(e), consider:
History and etymology
Iliac horns were described by Edward Everett Fong (b. 1912), an American radiologist.
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