Background
Metacarpal 4-5 fusion (MF4) is a rare congenital hand malformation characterised primarily by ulnar deviation of the fifth finger, clinodactyly, shortening of the fifth metacarpal and reduced mobility of the fifth finger. A small number of familial cases have been described in the literature, consistent with X-linked recessive inheritance. In May 2013 causative mutations in the FGF16 gene were identified in two unrelated patients with MF4.[1] This prompted the sequencing of FGF16 in half-brothers with MF4, with a view to identifying a possibly causative mutation.