In contrast to severe deficiency, some variants in MTHFR yield mild hyperhomocysteinemia (15–30 μM), which increases the risk of neural-tube birth defects and has been reported to increase the risk of cardiovascular disease,19,20 although the latter association is controversial,21,22 and of neural-tube birth defects.23 The gene discussed is MTHFR; the disease is hyperhomocysteinemia.