Nail-patella syndrome. This entity, also known as hereditary osteo-onychodysplasia, is a genetic disease linked to a mutation in the gene encoding transcription factor LMX1B, mapped on the long arm of chromosome 9 (9q34). The manifestations include fingernail dysplasia, absent or hypoplastic patellae, the presence of posterior conical iliac horns, and abnormalities of the radial heads. Patients are also at risk for kidney disease and glaucoma.
Nickel contact dermatitis. Allergy to nickel is one of the most common causes of contact dermatitis in children. Infants may present with skin lesions corresponding to the location of snaps on their pajamas or other garments. Older children may show reactions to watches, chains, belt buckles, or earrings.