A Thai mother and son with distal symphalangism, hypoplastic carpal bones, microdontia, dental pulp stones, and narrowing of the zygomatic arch: a new distal symphalangism syndrome?

A Thai mother and son with distal symphalangism and other associated abnormalities are reported. Distal and middle phalanges of fingers and toes 2-5 were either aplastic/hypoplastic or fused between the corresponding digits. The second fingers and fourth fingernails were most severely affected in both patients. The mother's hands were less severely affected; the middle and distal phalanges of her hands were malformed and fused. Besides the absence of fusion lines, the shape of the fused middle and distal phalanges was quite different from that of other types of fusion, i.e., fused bones in both patients did not maintain the normal configuration of bone, referring to as "middle-distal phalangeal complex". Distal symphalangism was observed in toes 2-5 of the mother and in toe 3 of the son. Both patients had additional clinical manifestations such as narrowing of the zygomatic arch, dental pulp stone, microdontia of a mandibular permanent central incisor, cone-shaped epiphyses of middle phalanges of fingers, and absence of scaphoid, trapezium, trapezoid, and pisiform bones. Mutation analysis of NOG and ROR2, the genes responsible for proximal symphalangism and brachydactyly type B, respectively, was negative.