Coffin–Siris syndrome
Coffin–Siris Syndrome is a rare genetic disorder that causes developmental delays and absent fifth finger and toe nails. There had been 31 reported cases by 1991. The number of occurrences since then has grown and is now reported to be around 80. The differential includes Nicolaides–Baraitser syndrome. Causes. Autosomal dominant inheritance is the most likely, usually by de novo mutation. This syndrome has been associated with mutations in the ARID1B gene. Mutations in SOX11 are associated to this syndrome. A second gene that has been associated with this syndrome is the AT-rich interaction domain  2 (ARID2) gene. The diagnosis is generally based on the presence of major and at least one minor clinical sign and can be confirmed by molecular genetic testing of the causative genes. Recent studies revealed that fifth finger nail/distal phalanx hypoplasia or aplasia is not a mandatory finding. Typically, lab work will be done to rule out other conditions and genetic testing will also be performed to get the official diagnosis. Treatment. There is no known cure or standard for treatment. Treatment is based on symptoms and may include physical, occupational and speech therapy and educational services as well