Malformation of the Extremity in the Mouse Foetus Caused by X-radiation of the Mother during Pregnancy.

W H I L E producing malformations in the mouse foetus with X-rays, the authors recognized an abnormal shortening of the extremities in a group treated on the 11th day of pregnancy. Such shortenings were caused by the absence, shortening, curvature, flexure or synostosis of the long bones of the extremities. Furthermore, in foetuses treated on the 12th day of pregnancy, numerous cases of ectrodactylism were found. Recently it has been noted that thalidomide taken during the early stages of pregnancy is liable to produce congenital malformations of the extremities such as phocomelia, defects of radii and thumbs, ectrodactylism, etc. in human beings. Lenz & Knapp (1962) pointed out that there is a critical stage when such serious malformations of the extremities caused by the use of the drug become manifest. The critical stage for the onset of serious malformation of extremities in the mouse foetus resulting from X-radiation corresponded well with the critical stage of the reduction malformations of the extremity caused by thalidomide. This paper describes an experimental attempt, using laboratory animals, to determine the critical stage for certain other malformations known in human beings. It also describes a mechanism responsible for ectrodactylism.