Nail–patella syndrome is a genetic disorder that results in small, poorly developed nails and kneecaps, but can also affect many other areas of the body, such as the elbows, chest, and hips.

It can reveal itself either rapidly or years after having asymptomatic deposition of protein in the urine, kidney failure occurs in around 5% of NPS patients.

Hypothyroidism, irritable bowel syndrome, attention deficit hyperactivity disorder (ADHD), and thin tooth enamel are associated with NPS, but whether these are related or simply coincidences are unclear.

The lack of development or complete absence of fingernails results from the loss of function mutations in the LMX1B gene.

This mutation may cause a reduction in dorsalising signals, which then results in the failure to normally develop dorsal specific structures such as nails and patellae.