Dysmorphism in One of a Set of Male Twins; Could They have been Identical Twins? A Diagnostic Dilemma

Twinning occurs worldwide, but Nigerian women of the southwest extraction record one of the highest rates in the world. Among the notable risk factors for fraternal twinning is advanced maternal age, which is also an independent risk factor for Down syndrome. Even as morphological characteristics can easily be applied to distinguish identical from fraternal twins, in cases of an associated dysmorphism, in any member of the couplet, it becomes a difficult tool to use, as has been observed in the case of a set of twins who were of the same sex, blood group, hemoglobin genotype, and shared the same placenta.