Asplenia syndrome in one of mono-zygotic twins

One of mono-zygotic twins who had the asplenia syndrome with severe cardiac malformations is described, the other twin being normal. This is the first documented case of situs ambiguus in mono-zygotic twins. The relationship of situs ambiguus to situs inversus, which has previously been described in a number of mono-zygotic twin pairs (some concordant and some discordant) is unclear.