Moreover, by combining APP/PS1 characteristics with a mutation in cystathionine-beta-synthase, a mouse model with significantly elevated serum homocysteine levels was generated and used to investigate hyperhomocysteinemia that, beside genetic alterations, can result from dietary deficits (e.g., folate, vitamin B6 and B12) and is considered an AD risk factor [200]. The gene discussed is PSEN1; the disease is Alzheimer disease.