Isolated cleft palate in Danish multiple births, 1970-1990.

The etiology of most cases of isolated cleft palate (CP) is unknown. The relative importance of genes and environment can be studied using the classical twin method but only few and potentially highly selected CP twin data are available. The present CP twin study was based on four Danish nationwide ascertainment sources of CP multiple births in the period 1970-1990. The ascertainment sources covered the time period from 15 completed weeks of pregnancy to adolescence for the older cohorts. A total of 18 CP cases in multiple births were identified; two monozygotic twin pairs of which one was concordant and eight were dizygotic, discordant twin pairs. Three cases were from two triplet sets, and four discordant twin pairs were of unknown zygosity. The twin concordance rates suggest that genetic factors play a major role in the etiology of CP, but environmental and/or stochastic factors are probably acting as well.