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Phenotypic and Molecular Evaluation of a Chromosome 1q Region with Linkage and Association to Type 2 Diabetes in Humans

Division of Endocrinology (H.W., S.K.D., R.L.C., W.S.C., N.S., S.C.E.), Department of Internal Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205; Research and Medicine Services (H.W., S.K.D., S.C.E.), Central Arkansas Veterans Healthcare System, North Little Rock, Arkansas 72114; and Nutrition, Metabolism, and Exercise Laboratory (N.P.H.), Donald W. Reynolds Department of Geriatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205

Address all correspondence and requests for reprints to: Steven C. Elbein, M.D., Endocrinology 111J/LR, John L. McClellan Veterans Hospital, 4300 West 7th Street, Little Rock, Arkansas 72205. E-mail: elbeinstevenc{at}uams.edu.

Objective: Linkage to type 2 diabetes (T2D) is well replicated on chromosome 1q21-q23. Within this region, T2D was associated with common single nucleotide polymorphisms that marked an extended linkage disequilibrium block, including the liver pyruvate kinase gene (PKLR), in several European-derived populations. In this study we sought to determine the molecular basis for the association and the phenotypic consequences of the risk haplotype.

Research Design and Methods: Genes surrounding PKLR were resequenced in European-American and African-American cases and controls, and association with T2D was tested. Copy number variants (CNVs) were tested for four regions with real-time PCR. Expression of genes in the region was tested in adipose and muscle from nondiabetic subjects with each genotype. Insulin secretion, insulin sensitivity, and hepatic glucose production were tested in nondiabetic individuals with each haplotype combination.

Results: No coding variant in the region was associated with T2D. CNVs were rare and not associated with T2D. PKLR was not expressed in available tissues, but expression of genes HCN3, CLK2, SCAMP3, and FDPS was not associated with haplotype combinations in adipose or muscle. Haplotype combinations were not associated with insulin secretion or peripheral insulin sensitivity, but homozygous carriers of the risk haplotype had increased hepatic glucose production during hyperinsulinemia.

Conclusions: Noncoding variants in the PKLR region likely alter gene expression of one or more genes. Our extensive physiological and molecular studies suggest increased hepatic glucose production and reduced hepatic insulin sensitivity, thus pointing to PKLR itself as the most likely candidate gene in this population.