Multifactorial inherited diseases are diseases which are caused by the interaction of genetic and environmental factors. Recurrence risk is low in multifactorial diseases as compared to single gene diseases and multifactorial diseases do not comply with Mendelian Genetics. However, it is difficult to predict and calculate the probability of recurrence. Therefore, certain empirical errors and risks may be inevitable in multifactorial diseases. The risk of recurrence is about 5% for the couples who already have a child with multifactorial disease.
Risk of existence in multifactorial diseases is lower for second degree of kinship than that of first degree of kinship as an index case. As the number individuals increase suffering from such multifactorial diseases within the family, the risk of recurrence also increase for new pregnancies. Those may have the disease who were previously less prevalent as one group of gender. Because these people are more sensitive for the disease; the risk of disease is higher for their relatives to occur as compared to the relatives of other sex who already have the disease.
One of the most common multifactorial diseases is neural tube defects (anencephaly, spina bifida, encephalocele). Neural tube defect manifests itself with varying degrees of closure defect in skull and spinal cord. Level of alpha-fetoprotein in the amniotic fluid in the open neural tube defects increases during pregnancy.
Neural tube defects are detected in women with children in the 2-3 months period before and after pregnancy folic acid treatment should be applied. Folic acid treatment should be applied to women having children with neural tube defects during 2-3 months before and after pregnancy.
Furthermore; pregnancy should be followed by ultrasonography and at 15th and 16th weeks of pregnancy, the level of fetoprotein (AFP) in maternal blood and in amniotic fluid taken via amniocentesis.