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

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Abstract
Different groups of the ddN strain mice were exposed to X-radiation of 300 r., 200 r. and 150 r. from the 8th to 13th day of pregnancy. In offspring from mothers treated on the 11th day, malformations of the extremities were observed in groups treated with over 200 r. Scapular hypoplasia and shortening of the fore-limb, as a result of absence, synostosis, shortening, flexure or curvature of the limb bone, etc., were typical malformations. However, in the group treated with 150 r. of X-radiations the incidence of such malformations was very low. In offspring from mothers treated on the 12th day, digital reductions, on account of ectrodactylias, were the typical malformation in the fore-limb. Ectrodactylia was dominant in the second digit of the fore-limbs, but involvement of the fifth digit was also seen. In the hind-limbs, the incidence was a little lower and the predominant site of involvement was the third digit. Both in the fore- and hind-limbs, the fourth digit was the most resistant to malformation. Other digital malformations occurred more often in the hind-limb than in the fore-limbs, though not frequently. The formation of ectrodactylias after X-radiation was studied in a follow-up experiment. The process began with cellular necrosis in the hand and foot plate corresponding to the predominant site of ectrodactylias, i.e. chiefly in the second digit of the fore-limb and in the third digit of the hindlimb. The process may damage the precursor of the pre-cartilage. In contrast to the regenerative neural tissue, compensation does not take place in the mesenchymal tissue once the destruction is severe, and the reduction of digits will therefore persist. The effect of X-radiation upon a developing digital primordium may be a directly destructive process. The critical stage for extremity malformations due to thalidomide in human beings corresponds with the critical stage for X-ray malformations of the extremities in mouse.