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Prenatally diagnosed de novo apparently balanced complex chromosome rearrangements: two new cases and review of the literature.

Complex chromosome rearrangements (CCR) are rare structural rearrangements. Currently six cases of prenatally diagnosed balanced de novo CCR have been described. We present two new cases of prenatally ascertained balanced de novo CCR. In the first case, an amniocentesis revealed a balanced de novo three-way CCR involving chromosomes 5, 6, and 11 with a pericentric inversion of chromosome 5 [four breaks]. In the second case, a balanced de novo rearrangement was identified by amniocentesis which involved a reciprocal translocation between chromosomes 3 and 8 and a CCR involving chromosomes 6, 7, and 18 [six breaks]. The use of whole chromosome painting helped elucidate the nature of these rearrangements. A review of the postnatally ascertained cases suggests that most patients have congenital anomalies, minor anomalies, and/or developmental delay/mental retardation. In addition, there appears to be a relationship between the number of chromosome breaks and the extent of phenotypic effects. The paucity of information regarding prenatally diagnosed CCR and the bias of ascertainment of postnatal CCR cases poses a problem in counseling families.