Multifactorial genetic diseases are that occur during the interaction of genetic factors abd environmental factors. Regarding these diseases that are not acting according to the mendelian genetic rules has relatively less recurrence risk to the single gene disorders. But this ratio sometimes fluctuates. It is difficult to measure the certain recurrence rate. Therefore they have some empirical risks. The risk of recurrence for a couple whose child suffers this disease is 5%.

At multifactorial diseases the risk of occurring the disease is much less at the second level relatives than those at first level. The more people carrying disease in the family, the more recurrence is the risk.

One of the mostly seen multifactorial diseases is neural tube defects (anencefaly, spina bifida, ensefalosel). Neural tube defect shows itself at skull and spinal cord by closing defect in different degrees. In the period of pregnancy at th open neural tube defects, the increases level of alpha-fetoprotein (AFP) in the liquid of amniotic.

At the women whose children have neural tube defects folic acid treatment should be used during the period of 2-3 months before and after their pregnancies. Besides the pregnancy should be followed via ultrasonography, and also in the maternal blood and in the amniotic fluid AFP levels should be checked via amniocentesis.