Several studies have shown that healthy individuals with fasting plasma glucose (FPG) levels at the high end of the normal range have an increased risk of mortality. To identify genetic determinants that contribute to interindividual variation in FPG, we tested 392,935 single-nucleotide polymorphisms (SNPs) in 654 normoglycemic participants for association with FPG, and we replicated the most strongly associated SNP (rs560887,
P= 4 × 10 –7 ) in 9353 participants. SNP rs560887 maps to intron 3 of the G6PC2gene, which encodes glucose-6-phosphatase catalytic subunit–related protein (also known as IGRP), a protein selectively expressed in pancreatic islets. This SNP was associated with FPG (linear regression coefficient β = –0.06 millimoles per liter per A allele, combined P= 4 × 10 –23 ) and with pancreatic β cell function (Homa-B model, combined P= 3 × 10 –13 ) in three populations; however, it was not associated with type 2 diabetes risk. We speculate that G6PC2regulates FPG by modulating the set point for glucose-stimulated insulin secretion in pancreatic β cells.