Brachydactyly type C.

Brachydactyly type C is an autosomal dominant disorder with markedly variable penetrance. A patient with limited gene expression has shortening limited to the middle phalanges and the first metacarpal and an elongation of the radial side of the base of the second proximal phalanx. When completely expressed the characteristic radiographic findings are shortening of all the metacarpals, greatest in the thumb, followed by the little, ring, middle, and index fingers; brachymesophalangy (shortening of the middle phalanges); shortening of the proximal phalanges of the index and middle fingers, with the proximal phalanges of the ring and small fingers of normal length; elongation of the radial side of the base of the second proximal phalanx resulting in a trapezoidal shaped epiphysis; ulnar deviation at the second and third metacarpophalangeal joints; and hypersegmentation (extra phalanx) of the index and middle fingers. The ulnar deviation of the index and middle fingers may result in scissoring and require surgical correction. The hand deformities of 10 patients with brachydactyly type C are presented to characterize the hand abnormalities in the syndrome and its variable presentation.