A routine prenatal ultrasound reveals a male fetus with meningomyelocele. The 24-year-old primigravid mother is told the infant will require surgery shortly after birth. You counsel her about the etiology of this defect and the risk of further pregnancies being similarly affected, and state which of the following?

Diseases that are due to defects in a single gene are designated as autosomal or X-linked, depending on whether the affected gene is located on an autosome or an X chromosome. Genetically determined diseases that are multifactorial in origin (ie, neural tube defects) do not conform to the Mendelian pattern of inheritance but exhibit a variable outcome that reflects the interaction between a particular genotype and an environment. The relatives of persons with diseases of multifactorial origin have an increased risk of having similar abnormalities.The recurrence risk for most single primary defects of multifactorial inheritance (eg, neural tube defects) is increased with each child affected. This increased risk forms the basis for assuming that genetic factors play a role in the occurrence of these abnormalities. Other factors, such as race, sex, and ethnic and racial background, influence the frequency with which an abnormality of multifactorial inheritance occurs in relatives The prenatal diagnosis of neural tube defects (anencephaly and meningomyelocele) can be made by the detection of elevated levels of alpha- fetoprotein in the amniotic fluid. To reduce the risk of neural tube defects, it is now recommended that all women capable of becoming pregnant take between 400 mcg and 800 mcg of folic acid daily.