Hypospadias is related to birth weight in discordant monozygotic twins

Purpose: Hypospadias is a common urogenital malformation in boys. The etiology is unknown but genetic and environmental factors are involved. Because monozygotic twins have the same genetic constitution, we studied disease discordant twin pairs to evaluate environmental risk factors while controlling for genetic effects. Materials and Methods: We used questionnaires to identify 28 male twins discordant for hypospadias at 4 pediatric surgical clinics in Sweden. Using deoxyribonucleic acid fingerprinting, and histopathological examination of the placenta and fetal membranes 18 twin pairs were diagnosed as monozygotic. Results: In 16 of the 18 monozygotic pairs discordant for hypospadias the twin with the lowest birth weight has hypospadias. Mean difference in birth weight was 498 gm. (t = 3.8, p <0.01). Conclusions: Environmental factors associated with low birth weight are involved in the etiology of hypospadias.