Postaxial polydactyly of the hand in Japanese patients: Case series reports.

PURPOSE: The incidence of postaxial polydactyly of the hand is rare in Japan. This study aimed to compare the clinical presentation of postaxial polydactyly between a cohort of patients from Japan and those from other racial and ethnic backgrounds. METHODS: In this retrospective study, we included 30 patients who were treated at our hospital during a 25-year study period (1990-2015). Based on the clinical records of these patients, we characterized the Japanese presentation of the condition. We searched for studies that included other racial and ethnic groups and characterized the clinical presentations. Then, we compared the clinical presentations between Japanese patients and other racial and ethnic groups. RESULTS: A total of 19 male and 11 female patients were treated in our hospital, and bilateral and unilateral involvements (right side: 4 patients; left side: 4 patients) were observed in 22 and 8 patients, respectively. Moreover, 22 postaxial polydactylies were type A and 28 polydactylies were type B, which were classified using the Temtamy-McKusick classification system. In addition, 4 patients had a family history of hand postaxial polydactylies; 18, 6, 4, and 3 patients presented with polydactyly of the foot, syndactyly, systemic abnormalities, and related syndromes, respectively. CONCLUSION: Japanese patients had two distinguishing characteristics: (1) when the condition was unilateral, left side and right side involvement was almost equal with regard to incidence and (2) associated polydactylies of the foot were more common (60%) than those in other cohorts (less than 31%). To better understand postaxial polydactyly of the hand, guidelines to record the clinical presentations in patients with such a condition must be developed.

Clinical and genetic studies on 12 preaxial polydactyly families and refinement of the localisation of the gene responsible to a 1.9 cM region on chromosome 7q36.

Polydactyly is the most frequently observed congenital hand malformation with a prevalence between 5 and 19 per 10000 live births. It can occur as an isolated disorder, in association with other hand/foot malformations, or as a part of a syndrome, and is usually inherited as an autosomal dominant trait. According to its anatomical location, polydactyly can be generally subdivided into pre- and postaxial forms. Recently, a gene responsible for preaxial polydactyly types II and III, as well as complex polysyndactyly, has been localised to chromosome 7q36. In order to facilitate the search for the underlying genetic defect, we ascertained 12 additional families of different ethnic origin affected with preaxial polydactyly. Eleven of the kindreds investigated could be linked to chromosome 7q36, enabling us to refine the critical region for the preaxial polydactyly gene to a region of 1.9 cM. Our findings also indicate that radial and tibial dysplasia/aplasia can be associated with preaxial polydactyly on chromosome 7q36. Combining our results with other studies suggests that all non-syndromic preaxial polydactylies associated with triphalangism of the thumb are caused by a single genetic locus, but that there is genetic heterogeneity for preaxial polydactyly associated with duplications of biphalangeal thumbs. Comparison of the phenotypic and genetic findings of different forms of preaxial polydactyly is an important step in analysing and understanding the aetiology and pathogenesis of these limb malformations.