The invention concerns an adenosylhomocysteinase (AHCY) binding substance for use in the treatment of deficiency of function of AHCY in a human being or an animal, wherein the AHCY binding substance is the cofactor nicotinamide adenine dinucleotide (NAD+), or an analogue of the cofactor NAD+ which analogue binds to an NAD+ binding site of AHCY, or an analogue of a substrate of AHCY which analogue binds to a substrate binding site of AHCY.
