Twins discordant for 46,XX gonadal dysgenesis.

This case report describes twin sisters, one with rudimentary streak gonads and the other with normal ovarian function. Both siblings had normal 46, XX karyotypes, and zygosity testing indicated that they were identical twins. Discordance of identical twins for 46, XX pure gonadal dysgenesis suggests that environmental factors may be a causative factor in some of the karyotypically normal 46,XX forms of gonadal dysgenesis.