Extrahepatic biliary atresia and twinning.

1. Four pairs of discordant twins were observed in a series of 237 extrahepatic biliary atresia patients ascertained in London. 2. The twinning prevalence (1.7%) was as expected considering the ethnic composition of the sample. 3. Out of a total of 17 other twin pairs reported in the literature, only one was concordant for the disease. Since only 17 instances of familial cases have been described, the conclusion is that any influence of genetic factors in this condition is likely to be manifested indirectly, possibly in the form of increased susceptibility of the biliary epithelium to infectious or toxic agents.