Syndactyly: frequency of specific types.

Syndactyly without other combined limb anomalies, Poland complex, or amniotic bands, was diagnosed in 174 of 599, 109 consecutive newborn infants (3/10,000). Syndactyly was the only diagnosed anomaly in 133 cases, and it was associated with other anomalies in 41. The most common type of syndactyly was isolated syndactyly of the second and third toes (70 cases), which affected more males than females, and had a higher than expected frequency of white non-Latin-European ancestry. The second most frequent type was isolated syndactyly of the middle and ring fingers (18 cases), and the third was isolated syndactyly of the fourth and fifth toes (13 cases). Considering both isolated and syndromal cases, 66% (114/172) could be assigned to one or another of the fourth genetic categories of syndactyly described by Temtamy and McKusick [1978]. This, plus the high frequency of affected first degree relatives observed (25/434:6%), suggests that the genetic forms of syndactyly may be more common than might be suspected from the small number of pedigrees in the literature.