We present an evaluation of the diagnosis, management and outcome of a pair of heterokaryotypic monozygotic dichorionic twins. The heterokaryotype was an incidental finding from an amniocentesis performed for prenatal diagnosis of beta-thalassaemia major in a pair of dichorionic twins. Monozygocity was revealed by QF-PCR showing identical short tandem repeat markers on chromosomes 21, 18, 13, X and Y. The twins were heterokaryotypic for duplication chromosome 2q13-q23.3, as shown by array comparative genomic hybridization. Selective foeticide was performed. This case demonstrates that heterokaryotypic monozygotic dichorionic twins are a genetic possibility that does occur.
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