Which amino acid is associated with neural tube defects?

Homocystine is the amino acid that is significantly associated with neural tube defects (NTDs), which are serious birth defects of the brain and spinal cord. Elevated levels of homocysteine have been implicated in the teratogenic effects that can lead to the development of NTDs during early pregnancy. The relationship is largely attributed to the role of folate metabolism in pregnant women; inadequate folate levels can lead to increased homocysteine levels. Folate is crucial for DNA synthesis and repair, and a deficiency can disrupt normal cellular processes, potentially resulting in neural tube malformations.

Regarding the other amino acids listed: glutamate and serine play important roles in neurotransmission and other physiological functions but do not have a direct association with neural tube defects. Cysteine, while an important amino acid, does not have the same established relationship with NTDs as homocystine does. Hence, the prominence of homocystine in this context highlights its critical role in developmental processes and folate metabolism, underscoring why it is the correct choice when discussing the association with neural tube defects.