Type 1 sirenomelia in one of male twins, with imperforate anus in the other male twin.

The etiology of sirenomelia sequence is still obscure. The role of maternal diabetes and a vascular steal phenomenon have been discussed [Gürakan et al. (1996) Turk J Pediatr 38:393-397]. Discordant monozygotic twin sirenomelia has been commonly reported but only rarely in dizygotic twins. The family of the presented twins had a high risk of diabetes mellitus. One of the twins has type 1 sirenomelia and the other had only an imperforate anus.