Although 5 other 46,XX males with the MIDAS syndrome have been describedin the literature, this study represents the first case report of identicaltwin boys (cases 1 and 2). These 2 cases demonstrate that, even with identicalgenetic deletions at the Xp22.3 locus, the phenotypes may vary. Patients 1and 2 were similar in that both of them had microphthalmia, sclerocornea,and skin deformities. They also exhibited hypospadias and a mild cardiac abnormalityin the form of SVT. There were, however, several differences in the phenotypesof the twins. Patient 1 had a definite high elevation of IOP, while patient2 had a borderline elevation of pressure. Patient 2 had a small right eyelidfissure and anophthalmia, neither of which was present in patient 1. Microcorneawas present in patient 1, but the corneal diameter of the nonanophthalmicleft eye of patient 2 was normal. These phenotypic differences found in identicaltwin boys with identical karyotypes lend further support to the current hypothesisthat the variations found in MIDAS syndrome may be due to different patternsof X inactivation, or lyonization, rather than due to subtle differences ingenotypes.4,5 Further researchshould be done to understand more completely how the Xp22.3 deletion is expressedbecause this research may lead to a better understanding of the role of thischromosomal locus in ocular development.