Purpose or Case Report:
Nail-patella syndrome (NPS) is a multisystemic autosomal dominant disease with neurologic, ocular, renal, and musculoskeletal manifestations. The incidence of NPS is reportedly 1 in 50,000, although this may be an underestimate due to its phenotypic variability allowing this disease to remain undiagnosed for multiple generations. A loss of function mutation of the LMXB1 gene, which influences dopaminergic and serotonergic neuronal differentiation, periocular mesenchymal development, renal podocyte development, limb patterning, and skull patterning, leads to NPS. Clinical findings include open-angle glaucoma, ocular hypertension, neuropathic pain and numbness/tingling, and renal failure. Absent, hypoplastic, or dystrophic fingernails are noted in 98% of cases. Almost all patients present with absent, hypoplastic, or irregular patellae that frequently sublux. About 70% of patients present with pathognomic iliac horns, which are corticomedullary processes continuous with the iliac bones at the gluteus medius muscle origin. Loss of skin creases over the distal interphalangeal joints is also a sensitive finding for NPS. Decreased extremity muscle mass and bone formation can lead to limited knee and elbow joint range of motion.

The subject of this case report is a 20-year-old female who presented to nephrology clinic for proteinuria. Onychia was noted on physical exam. Past medical history was significant for spastic diplegia, and surgical history included epiphysiodesis due to leg length discrepancy. The patient was relatively asymptomatic otherwise. CT of the pelvis demonstrated bilateral osseous excrescences of the iliac bones. Absence of the patella and posterior subluxation of the radial head were noted on radiographs. CT of the abdomen showed bilateral renal atrophy. Subsequent renal biopsy demonstrated findings consistent with NPS. The patient was placed on hemodialysis after progressing to renal failure.

The prognosis of NPS is favorable with proper screening precautions and early intervention; however, complications of this disease can lead to poor outcomes. Imaging is critical in diagnosing NPS through its musculoskeletal findings on radiography. Characteristic findings include small or absent patella, pathognomic bilateral iliac horns, abnormalities of the femoral condyles and trochlea, and radial head dysplasia/subluxation.
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