The etiology of sirenomelia sequence is still obscure. The role of maternal
diabetes and a vascular steal phenomenon have been discussed [Gurakan et a
l. (1996) Turk J Pediatr 38:393-397]. Discordant monozygotic twin sirenomel
ia has been commonly reported but only rarely in dizygotic twins. The famil
y of the presented twins had a high risk of diabetes mellitus. One of the t
wins has type 1 sirenomelia and the other had only an imperforate anus. Cli
n Dysmorphol 9: 227-229 (C) 2000 Lippincott Williams & Wilkins.