Rs63749884

rs63749884, also known as M239I or Met239Ile, is a SNP in the presenilin 2 PSEN2 gene.

Inherited as an autosomal dominant, the rare rs63749884(A) allele is considered causative for early-onset Alzheimer's disease; see. However, only three of the five individuals in the family studied who carried this mutation developed Alzheimer's; the other two did not. The penetrance of this mutation is therefore clearly not 100%, for reasons that are unknown.