Brachydactyly absence of distal phalanges
Overview
Congenital hyponychia and anonychia are rare malformations which may form part of syndromes such as nail–patella syndrome, ectodermal dysplasias and brachydactylies, or may occur as an isolated finding. Congenital hyponychia and anonychia are frequently accompanied by underlying skeletal abnormalities. A 20-year-old woman showed congenital bilateral hypoplasia or aplasia of the second, third and fourth toenails with corresponding phalanx dysplasia or aplasia of the affected toes. Malformations of the hands or other congenital defects were absent. The findings in this patient do not exactly fit any known entities. Our clinical observation prompted us to review the literature on congenital hyponychia/anonychia and to summarize recent advances in understanding molecular events in nail development. In conclusion, the association of nail anomalies with aplasia and/or hypoplasia of corresponding middle and/or distal phalanges supports the hypothesis of bone-dependent nail formation.
Causes
BDB is caused by heterozygous nonsense or frameshift mutations located distally and proximally of the TK domain. These mutations lead to truncation of the intracellular serine-threonine-rich, and proline-rich domains, or of the entire intracellular portion of the receptor. In contrast missense or nonsense mutations leading to amino acid exchange or truncation of extracellular domains of ROR2, truncation within the TK domain, or selective inactivation of TK activity lead to autosomal recessive Robinow syndrome.