HAND AND FOOT POSTAXIAL POLYDACTYLY - 2 DIFFERENT TRAITS

The aim of this work was to test whether postaxial hexadactyly had dif ferent clinical and epidemiological characteristics depending on hand or foot involvement. In the period 1967-1993, the Latin-American Colla borative Study of Congenital Malformations (ECLAMC) enrolled 1,582,289 births, and 2,271 cases with isolated (nonsyndromal) postaxial polyda ctyly (5th-digit hexadactyly). The prevalence was 14.3/10,000 births. Postaxial polydactyly (PP) of the hand (HPP) was the most frequent typ e (N:1,733; 78.3%; prevalence: 11.0/ 10,000), followed by foot PP (FPP =N:351; 15.5%; prevalence: 2.2), and hand and foot PP (BPP=N:187; 8.2% ; prevalence: 1.2). Unlike HPP (55.0% bilateral; 77.2% left), FPP was less frequently bilateral (19.4%), with lower preference for the left side (55.5%). As expected, HPP was associated with African Black ethni city, male sex, twinning, low maternal education, parental consanguini ty, and there was frequent recurrence in Ist-degree relatives. Convers ely, FPP was associated with Amerindian racial background, parental su bfertility, and bleeding in the Ist trimester of pregnancy. BPP displa yed the highest frequency of associated congenital defects (23.4%, vs HPP:6.6%, FPP: 15.4%). In its isolated form, BPP resembled HPP more th an FPP with respect to left preference (90.9%), familial recurrence (1 1.0% of 1st degree relatives), and low maternal education. Although ma le sex preference and high frequency of twinning was observed in the 3 PP subtypes, statistical significance was present only in HPP. None o f the 3 PP subtypes showed abnormal values for perinatal mortality, bi rth weight, length of gestation, parental ages, or parity. A logistic regression analysis showed Black race only to be associated with HPP, parental subfertility with FPP, parental consanguinity with BPP, and n on-Black race with both FPP and BPP. The data presented here are the f irst indication that HPP and FPP are 2 different entities, with a larg er genetic component in HPP than in FPP. (C) 1997 Wiley-Liss, Inc.