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Periconceptional folic acid (pteroylglutamic acid) supplementation or the fortification of staple foods with folic acid have been shown to reduce the risk for pregnancies with neural tube defects (NTDs).1–4 However, mechanistic link(s) between this increased intake of folic acid and NTD prevention remains unclear. Homozygous or heterozygous variants of the thermolabile 5,10-methylenetetrahydrofolate reductase (MTHFR) gene have also been associated with a high risk for NTDs.5–7 We recently reported the association of NTDs with MTHFR genotypes using fetal cells of NTD cases and their controls obtained between 1988 and 1998. The fetuses with either heterozygous or homozygous genotypes of MTHFR had a higher risk for NTDs than those with wild type.7
Further analysis of the data indicated a drastic change in the frequency of the heterozygous genotype of MTHFR among 77 NTD affected fetuses starting in 1994. However, no such change was found in 77 control fetuses (controls) without malformations, who were matched for race, maternal age, and time of amniocentesis. The mean maternal age was 28 years old and the subject population consisted of 84% whites and 16% African-Americans. The diagnosis of NTDs was made by ultrasound examination and amniocentesis and confirmed by neonatal examination or necropsy.7 The amniotic fluid samples were obtained aseptically under ultrasound guidance at the University of Alabama Prenatal Genetics Clinic. The study was approved by the Institutional Review Board for Human Use of the University of Alabama at Birmingham. Amniotic fluid samples were stored at −70°C until analysis and those obtained between 1988 and 1998 were available for the analysis. Polymorphisms of the MTHFR gene were determined by polymerase chain reaction.8 The fetuses homozygous …