EPIDEMIOLOGIC ANALYSIS OF RARE POLYDACTYLIES

This work includes all cases with extra digits (polydactyly) registere d from a birth sample of over four million births aggregated from two comparable birth series: the Latin-American Collaborative Study of Con genital Malformations: ECLAMC (3,128,957 live and still births from th e 1967 to 1993 period), and the Spanish Collaborative Study of Congeni tal Malformations: ECEMC (1,093,865 livebirths from April 1976 to Sept ember 1993, and 7,271 stillbirths from January 1980 to September 1993) . All but 2 of 6,912 registered polydactyly cases fit well into one of the following 11 preestablished polydactyly types (observed number of cases in parentheses): Postaxial hexadactyly (5,345), Preaxial-I hexa dactyly (1,018), Seven or more digits (57), synpoly-dactyly (15), cros sed polydactyly (45), Ist digit triphalangism (33), 2nd digit duplicat ion (39), 3rd digit duplication (18), 4th digit duplication (22), Haas polysyndactyly (3), and high degree of duplication (4). The birth pre valence rates observed in both series were similar except for postaxia l polydactyly, which was more frequent in the ECLAMC (150.2/100,000) t han in the ECEMC (67.4/100,000), as expected due to the higher African Black ethnic extraction of the South-American than of the Spanish pop ulations. This similar frequency for the rare polydactylies (5.4 per 1 00,000 in South America and 5.7 in Spain), and for each one of the 9 c ategories, suggests that the values reported here are valid for most p opulations. The rare polydactylies are frequently syndromal: one third of them (77/236) were found in association with other congenital anom alies, 11.0% (26/236) in MCA cases and 21.6% (51/236) in recognized sy ndromes. (C) 1996 Wiley-Liss, Inc.