Previous studies have found associations between T1D and known T2D loci including in the melatonin receptor 1B (MTNR1B) and HNF1A [17], and results from a multiancestry GWAS for T2D showed that POU5F1-TCF19 and HLA-DRA within the major histocompatibility complex was associated with T2D in addition to INS, TH, CTRB1, and CENPW [15] (Table S3 [28]). Here, CTRB1 is linked to type 1 diabetes mellitus.