Complete blood count, vitamin B12 and folate levels, plasma amino acid levels and assessment of kidney function can also be valuable to evaluate whether the elevated Hcy levels represent a diagnosis of classic homocystinuria or other etiologies, such as renal disease, vitamin B12 or folate deficiency, MTHFR deficiency, or a disorder of intracellular cobalamin metabolism. This evidence concerns the gene MTHFR and homocystinuria.