Retinoic-acid-induced limb malformations resulting from apical ectodermal ridge cell death

Pregnant C57Bl/6J mice were treated with single oral doses of 400 mg/kg 13-cis retinoic acid (RA, isotretinoin, Accutane) in sesame oil at 9 days, 12 hours postfertilization. Among the live 16-day fetuses from ten treated mothers, 46% (26/56) had limb malformations including small fifth digits, preaxial and/or postaxial oligodactyly, and preaxial or postaxial polydactyly. Fetuses with preaxial digit deficiencies also had absent or malformed radii. Scanning electron microscopic and light microscopic analyses of the sequence of developmental alterations leading to these malformations demonstrated abnormalities in the apical ectodermal ridge (AER). Excessive cell death in the AER of 27-30 somite embryos (12 hours after treatment) appears to play a major role in the pathogenesis of the limb malformations observed. Previous investigations of retinoid-induced limb malformations have concentrated on later exposure times. Evidence from this study in addition to that from previous teratologic and clinical investigations has led to the hypothesis that 13-cis RA results in excessive cell death in regions of programmed cell death and subsequent malformations of affected regions.