CST3 and diabetes mellitus: Furthermore, since genome-wide association studies (GWAS) for genetic determinants of cystatin C have identified the strongest signal of the genome associating with variation of plasma concentration of cystatin C at the cystatin C locus on chromosome 20, represented by the single nucleotide polymorphism (SNP) rs13038305 [15], we set out to investigate if there was a causal association between cystatin C and glucometabolic disease by relating rs13038305 (major allele) to the development of MetS and diabetes.