MTHFD1L and Alzheimer disease: The late-onset AD accounts for the major cases of AD, notwithstanding a lack of full understanding, the genetic risk factors, such as the definitively identified apolipoprotein E (APOE) gene on chromosome 19 [18] and the methylenetetrahydrofolate dehydrogenase 1-like (MTHFD1L) gene on chromosome 6 [19] as well as some other loci [20,21,22,23], are likely to affect the predisposition of AD.