Animal Model for Congenital Anomalies Induced by Chromosome Aberrations *

Animal model for congenital anomalies induced by chromosome aberrations is explained in mice. Exencephaly is the most conspicuous external malformations among mice trisomies and partial trisomies. Characteristic cardiovascular malformations are observed in Ts 16, 13 and 14. The association of persistent common atrioventricular (A‐V) canal in Ts 16 provides an excellent morphological homology to human trisomy 21. Observations on A‐V canal endocardial cushions of Ts 16 fetuses showed i) hypoplastic endocardial cushions, ii) delayed appearance of mesenchymal cells into cushions. and iii) failed fusion of endocardial cushions. The conotruncal malformations were observed in every fetus of Ts 16. Abnormal aortic arch was observed in about half of the cases. Further, the thymus was always hypoplastic. The combination of these anomalies suggests that Ts 16 had abnormal development similar to DiGeorge anomaly in these regions. In enlarged hearts of T hp and t wLub2 , which have deletions on chromosome 17, the ventricular septum bulged so extremely into ventricle that the bilateral ventricular outflow tract was markedly obstructed. From 14 days of pregnancy on, generalized edema was often observed in some of trisomic and T hP fetuses. Histological examination of Ts 16 and T hp fetuses demonstrated that the essence of the fetal edema was cystic hygroma, which is sometimes encountered in human fetuses with chromosome aberrations. Investigations by an animal model with chromosome aberrations did offer new information which remains somewhat scanty in early embryonic stage.