Pachyonychia congenital is a kind of familial anomaly of keratinized tissues such as skin, and nails. It is autosomal dominantly inherited. This anomaly affects the skin (palms and soles), nails and oral mucosa. Abnormalities of nails are apparent early in life. Nails are thickened (pachyonychia), often with brownish discolouration.  All finger nails are commonly involved. It is diagnosed usually by its clinical appearance.
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. The hallmark features of this syndrome are poorly developed fingernails, toenails, and patellae. Sometimes, this disease causes the affected person to have either no thumbnails or a small piece of a thumbnail on the edge of the thumb. 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. Other common abnormalities include elbow deformities, abnormally shaped pelvic bones, and kidney disease.
Twenty-nail dystrophy is also known as “trachyonychia”. The condition is characterized by longitudinal ridging, pitting, loss of lustre, and roughening of the nail surface. This condition appears to be associated with other conditions such as lichen planus, eczema, psoriasis, and alopecia areata, in some cases an autosomal dominant pattern of inheritance has been found