Cytogenetic and histological features of a human embryo with homogeneous chromosome 8 trisomy

Background Homogeneous and complete trisomy 8 is extremely rare. With one recent neonatal exception, all reported cases have been mosaic, due to mitotic non‐disjunction during early zygotic development. We report a case of chromosome 8 trisomy in a human embryo examined at Carnegie stage 11 (25 days post‐fertilization). It presented severe cardiovascular and central nervous system malformations. Methods The unusual bifid heart in this embryo spurred a detailed histological examination, karyotyping of a chorionic villus sample and subsequent FISH on inter‐phase nuclei of intra‐embryonic sections. Results Trophoblast cells had a karyotype of 47,XX, +8. Within the embryo proper, FISH demonstrated that the trisomy 8 was homogeneous in embryonic as well as extra‐embryonic tissues. FQ‐PCR supports a meiosis I origin of non‐disjunction. In sections, the pharyngeal arches (including cardiac outflow tract), forebrain, mesonephros and liver were absent. Somites and yolk sac blood vessels were irregularly shaped. Conclusion We show that homogeneous, intra‐embryonic trisomy 8 is compatible with implantation and early human development. Molecular pathways that may be compromised and their impact on organogenesis are discussed. Copyright © 2006 John Wiley & Sons, Ltd.