Biparental inheritance of non-mosaic 5-5 translocation
A 40 year old woman presented for prenatal diagnosis by amniocentesis at 17 weeks gestation. Ultrasound findings indicated growth retardation (measurements consistent with 15 weeks), the presence of a 2 vessel cord, bilateral choroid plexus cysts and fifth finger clinodactyly. Cytogenetic studies showed a non-mosaic translocation involving both chromosome 5s.The karyotype was 46,XX,t(5;5)(pter>q13.3::p15.3>pter;qter>q13.3::p15.1>qter). FISH studies using the probes for the Cri du chat region and ERG-1 showed deletion of the Cri du chat region on the smaller translocation product. One copy of this probe was observed on both chromosome spreads and two hundred interphase nuclei. UPD studies with markers for the p (D5S426) and q (D5S641) arms of chromosome 5 showed biparental inheritance. Biparental inheritance of a translocation appears to be very rare and has been reported only for homologous Robertsonian translocations. The pregnancy was terminated and the non-mosaic karyotype was demonstrated in fetal skin and chorionic villi sampled from several sites on the placenta. Interphase FISH studies of both tissues gave the same result. These findings provide further evidence for the existence of biparental inheritance of homologous translocations. The event must be of post-zygotic in origin and must occur within the first several cell divisions after fertilization as evidenced by non-mosaic state of chorionic villi; interphase FISH studies will examine both cytotrophoblast and mesenchymal cells.