rs4072037

rs4072037 is a synonymous A>G variant in exon 2 of MUC1 that does not change an amino acid but shifts alternative 3' splice-site selection between the MUC1/A and MUC1/B transcripts and is linked to variable-number-tandem-repeat (VNTR) length, altering mucin 1 expression in gut epithelium. The G allele is associated with modestly lower serum magnesium levels in GWAS, plausibly via increased mucin production in the intestinal mucosal barrier reducing magnesium absorption. It is used together with TRPM6 rs11144134 as a marker for genetic tendency toward blood magnesium status, a trait far more influenced by diet and kidney function than by these genes.