Medical Genetics B。 Environment Environmental causes(including exposure to drugs, radiation and illnesses) can be identified in about 10 per cent of birth defects. The risk of exposure to such environmental factors often causes great concern, although genetic causes are more commonMedical Genetics B. Environment Environmental causes (including exposure to drugs, radiation and illnesses) can be identified in about 10 per cent of birth defects. The risk of exposure to such environmental factors often causes great concern, although genetic causes are more common