93Hemoglobin A1c (HbA1c) is widely used to diagnose diabetes and assess glycemic control in 94 patients with diabetes. However, nonglycemic determinants, including genetic variation, may 95 influence how accurately HbA1c reflects underlying glycemia. Analyzing the NHLBI Trans-96 Omics for Precision Medicine (TOPMed) sequence data in 10,338 individuals from five studies 97 and four ancestries (6,158 Europeans, 3,123 African-Americans, 650 Hispanics and 407 East 98 Asians), we confirmed five regions associated with HbA1c (GCK in Europeans and African-99 Americans, HK1 in Europeans and Hispanics, FN3K/FN3KRP in Europeans and G6PD in 100 African-Americans and Hispanics) and discovered a new African-ancestry specific low-101 frequency variant (rs1039215 in HBG2/HBE1, minor allele frequency (MAF)=0.03). The most 102 associated G6PD variant (p.Val98Met, rs1050828-T, MAF=12% in African-Americans, 103 MAF=2% in Hispanics) lowered HbA1c (-0.88% in hemizygous males, -0.34% in heterozygous 104 females) and explained 23% of HbA1c variance in African-Americans and 4% in Hispanics.105Additionally, we identified a rare distinct G6PD coding variant (rs76723693 -p.Leu353Pro, 106 MAF=0.5%; -0.98% in hemizygous males, -0.46% in heterozygous females) and detected 107 significant association with HbA1c when aggregating rare missense variants in G6PD. We 108 observed similar magnitude and direction of effects for rs1039215 (HBG2) and rs76723693 109 (G6PD) in the two largest TOPMed African-American cohorts and replicated the rs76723693 110 association in the UK Biobank African-ancestry participants. These variants in G6PD and HBG2 111 were monomorphic in the European and Asian samples. African or Hispanic ancestry individuals 112 carrying G6PD variants may be underdiagnosed for diabetes when screened with HbA1c. Thus, 113 assessment of these variants should be considered for incorporation into precision medicine 114 approaches for diabetes diagnosis.115 116 6 157We included in our analyses 10,338 TOPMed participants without diabetes from five