Azathioprine teratogenicity: review of the literature and case report.

An infant born with preaxial polydactyly to a mother taking azathioprine throughout pregnancy is described. Experimental studies in animals reveal a teratogenic role for azathioprine and its main metabolite, 6-mercaptopurine. The skeletal system appears to be the primary tissue target for such action of these drugs. Although no direct cause-effect relationship can be established from the single case presented, the similarity of this anomaly to experimental azathioprine teratogenesis suggests the necessity for further surveillance.