Cleft of the lip and palate in twins.

BACKGROUNDS: Cleft lip and palate is one of the most common congenital anomalies in Taiwan. Its etiology remains unknown for the majority of the patients. The study of twins is a classic method for evaluating the relative roles of genetic and environmental factors in the formation of the anomaly. METHODS: In this study, 37 pairs of twins and one set of triplets with cleft lip and palate were evaluated. Clinical data were collected for zygosity determination and analysis of etiologic factors. The concordance rate and heritability index were assessed. RESULTS: The results showed that the concordance rate was 26% for all twins and 57% among the monozygotic pairs, which is higher than those rates for the Caucasian population. The heritability index was 53%, higher than the other reports as well. The influence of the environment could not be ruled out. CONCLUSION: The results confirm a strong genetic role in the etiology of clefts in our patients. Environmental factors were acting as well. The findings in this study support the multifactorial threshold model in the development of cleft lip and palate.