A decrease in alpha-fetoprotein levels in amniotic fluid is often associated with which condition?

A decrease in alpha-fetoprotein (AFP) levels in amniotic fluid is often associated with Down syndrome. Alpha-fetoprotein is a protein produced by the fetal liver, and its levels can provide important diagnostic information during pregnancy. In cases of Down syndrome, which is characterized by an extra copy of chromosome 21, the AFP levels typically are lower than expected. This reduction is thought to be related to the altered fetal physiology and biochemical pathways associated with chromosomal abnormalities.

In contrast, conditions such as spina bifida generally exhibit elevated AFP levels due to increased permeability of the fetal-neuronal barriers, leading to more AFP entering the amniotic fluid. Congenital diaphragmatic hernia is also associated with increased AFP levels due to the associated fetal distress and potential for fetal lung hypoplasia. Multiple sclerosis does not have a direct correlation with fetal AFP levels, as it is primarily an autoimmune disorder not affecting fetal development in this way.

Thus, the association of decreased AFP levels in amniotic fluid with Down syndrome is significant for prenatal screening and risk assessment for this chromosomal anomaly.