CNNM2 and Alzheimer disease: Variation of AD-inherited simple hypomagnesemia (type 1) contains a frameshift variant located near the N-terminal (p.Ile40SerfsX15), a missense variant in the CBS domain (p.Thr568Ile), and a stop-gain variant located in the CNBH domain, where p.Ile40SerfsX15 and p.Ser795* can cause changes in mRNA and protein length, and the structurally abnormal mRNA and proteins may be degraded, causing a decrease in intracellular CNNM2 expression, which affects the transmembrane transport of magnesium.