For instance, the finding on the MTHFR defects in homocystinuria due to MTHFR deficiency helps to explain why the supplementation of B12 did not improve the deteriorating nervous system for homocystinuria due to MTHFR deficiency patients and the use of CH3-THF cannot make the neurotransmitter normalized, whereas the use of betaine can effectively prevent the death of patients with early-onset of homocystinuria due to MTHFR deficiency and improve the dysplasia symptoms of the nervous system by remethylating of Hcy to Met [15, 16]. This evidence concerns the gene MTHFR and homocystinuria.