Suspected Causes of Human Birth Defects

Suspected Cause % of TotalGenetic Autosomal genetic disease 15-20 Cytogenetic 5Environmental Maternal conditions 4 Maternal infections 3 Mechanical Problems 1-2 Chemicals/drugs/radiation/hyperthermia <1Unknown 65

Human Developmental Toxicants I

• Radiation– Therapeutic– Radionuclide– Atomic fallout

• Infection– Rubella virus– Cytomegalovirus– Toxoplasmosis– Venezuelan equine

encephalitis virus– Syphilis– Parvovirus B-19– Varicella virus

• Maternal Trauma/Metabolic Imbalance– Alcoholism– Amniocentesis (early)– CVS before day 60– Cretinism– Diabetes– Folic acid deficiency– Hyperthermia– Phenylketonuria– Rheumatic disease– Sjogren’s syndrome– Virilizing tumors

Human Developmental Toxicants II

• Drugs/Chemicals– Androgens– ACE inhibitors

• Enalapril, captopril– Antibiotics

• Tetracycline– Anticancer drugs

• Cycloposphamide, busulfan– Anticonvulsants

• Diphenylhydantoin, trimethadione, valproic acid

– Antithyroid drugs• Methimazole

– Chelators• Penicillamine

– Chlorobiphenyls

– Cigarette smoke– Cocaine– Coumarin (warfarin)– Ethanol– Ethylene oxide– Fluconazole– Diethylstilbesterol– Iodides– Lithium– Metals

• Hg, Pb– Methylene blue– Misoprostol– Retinoids

• 13-cis retinoic acid, etretinate– Thalidomide– Toluene abuse

Critical Periods of Susceptibility (Wilson)

Critical Periods for Malformations in Humans Malformation Time of InductionCyclopia 23 daysAnencephaly 26 daysTransposition of great vessels 34 daysCleft lip 36 daysAplasia of radius 38 daysVentricular septal defects 6 weeksSyndactyly 6 weeksCleft palate 8-9 weeksBicornurate uterus 10 weeksHypospadias 12 weeksCryptorchidism 7-9 months