Congenital defects, or congenital malformations, are the defective formation of structures or body parts present at birth. Sporadic, hereditary, or acquired defects may be observed immediately or may appear later in life; they may be visible on the body surface or present internally. Birth defects can be life-threatening and require surgical correction, or they can interfere with function or appearance. It is estimated that approximately 3% of all children are born with serious defects; It is estimated that minor defects or variations occur in 10-15% of births. Malformations can be single or multiple. Multiple malformations that occur in a regular, recognizable pattern are called syndromes: for example, FETAL ALCOHOL SYNDROME sometimes seen in children of mothers who drank heavily during pregnancy. Birth defects can result from the action of genes, chromosomes, or the environment on the developing fetus, but it is often not possible to determine the cause. Hereditary defectsAbnormal genes cause a significant number of different birth defects. Some can be identified as monogenic disorders inherited in a simple Mendelian fashion, that is, with a dominant or recessive pattern. For example, lobster claw hand and foot deformity (split hands or feet) is hereditary and results from the effect of a single dominant gene. A person with this deformity has a 50% (1 in 2) risk of having children who will inherit the gene and will therefore also be affected. Autosomal reception...