Thiazolidinediones are a new class of antidiabetic agent that improve insulin sensitivity and reduce plasma glucose and blood pressure in subjects with type 2 diabetes. Although these agents can bind and activate an orphan nuclear receptor, peroxisome proliferator-activated receptor gamma (PPARgamma), there is no direct evidence to conclusively implicate this receptor in the regulation of mammalian glucose homeostasis. Here we report two different heterozygous mutations in the ligand-binding domain of PPARgamma in three subjects with severe insulin resistance. In the PPARgamma crystal structure, the mutations destabilize helix 12 which mediates transactivation. Consistent with this, both receptor mutants are markedly transcriptionally impaired and, moreover, are able to inhibit the action of coexpressed wild-type PPARgamma in a dominant negative manner. In addition to insulin resistance, all three subjects developed type 2 diabetes mellitus and hypertension at an unusually early age. Our findings represent the first germline loss-of-function mutations in PPARgamma and provide compelling genetic evidence that this receptor is important in the control of insulin sensitivity, glucose homeostasis and blood pressure in man.

Inherited defects in signaling pathways downstream of the insulin receptor have long been suggested to contribute to human Type 2 diabetes mellitus. Here we describe a mutation in the gene encoding the protein kinase AKT2/PKBβ in a family that shows autosomal dominant inheritance of severe insulin resistance and diabetes mellitus. Expression of the mutant kinase in cultured cells disrupted insulin signaling to metabolic end-points and inhibited the function of coexpressed, wild type AKT. These findings demonstrate the central importance of AKT signaling to insulin sensitivity in humans.Most forms of diabetes are likely to be polygenic in origin, although a number of monogenic forms are being recognised (1, 2). Although rare, these monogenic examples offer insights into the function of the affected gene in humans as well as offering important clues to understanding more common forms.We have been screening genomic DNA from 104 unrelated subjects with severe insulin resistance for mutations in genes that are implicated in insulin signalling. We identified a † To whom correspondence should be addressed. E-mail: sorahill@hgmp.mrc.ac.uk. * These authors contributed equally to this work. Europe PMC Funders Group Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts missense mutation in the serine/threonine kinase gene AKT2 in one Caucasian proband.AKT2 (also known as PKBβ) is highly expressed in insulin sensitive tissues and is activated in response to growth factors and related stimuli (3, 4) a process that requires its phosphorylation by the phosphoinositide-3 phosphate-dependent kinase activities designated PDK1 and PDK2 (3). The proband, (iii)/1 (Fig. 1D), is a non-obese 34 year old female who developed diabetes mellitus at 30 years of age. The proband, her non-obese mother, (ii)/2, maternal grandmother, (i)/2, and a maternal uncle, (ii)/3, were all heterozygous for a G to A substitution predicted to result in an R to H substitution at amino acid 274 (Fig. 1 A, B). All were markedly hyperinsulinemic (Table S1) and the mother and maternal grandmother developed diabetes mellitus in their late 30′s. Three other first-degree relatives available for study were all clinically normal with normal fasting glucose and insulin and were homozygous for the wild-type AKT2 sequence ( Fig. 1D and Table S1). This mutation was not found in genomic DNA of 1500 Caucasian control subjects from the UK.R274 forms part of an RD sequence motif within the catalytic loop of the AKT2 kinase domain that is invariant in AKT isoforms in all species, and is also highly conserved within the protein kinase family (Fig. 1C) (5). The RD motif includes the invariant D residue (D275 of AKT2) that performs an essential catalytic function in all protein kinases.R274 is positioned in the core of the catalytic domain, forming critical hydrogen bonds with the phosphate moiety of phosphoT309 in the activation segment permitting correct positioning the substrate peptide relative to the catalytic base and adenosine triphosphate (A...

Type 2 diabetes is an increasingly common, serious metabolic disorder with a substantial inherited component. It is characterised by defects in both insulin secretion and action. Progress in identification of specific genetic variants predisposing to the disease has been limited. To complement ongoing positional cloning efforts, we have undertaken a large-scale candidate gene association study. We examined 152 SNPs in 71 candidate genes for association with diabetes status and related phenotypes in 2,134 Caucasians in a case-control study and an independent quantitative trait (QT) cohort in the United Kingdom. Polymorphisms in five of 15 genes (33%) encoding molecules known to primarily influence pancreatic β-cell function—ABCC8 (sulphonylurea receptor), KCNJ11 (KIR6.2), SLC2A2 (GLUT2), HNF4A (HNF4α), and INS (insulin)—significantly altered disease risk, and in three genes, the risk allele, haplotype, or both had a biologically consistent effect on a relevant physiological trait in the QT study. We examined 35 genes predicted to have their major influence on insulin action, and three (9%)—INSR, PIK3R1, and SOS1—showed significant associations with diabetes. These results confirm the genetic complexity of Type 2 diabetes and provide evidence that common variants in genes influencing pancreatic β-cell function may make a significant contribution to the inherited component of this disease. This study additionally demonstrates that the systematic examination of panels of biological candidate genes in large, well-characterised populations can be an effective complement to positional cloning approaches. The absence of large single-gene effects and the detection of multiple small effects accentuate the need for the study of larger populations in order to reliably identify the size of effect we now expect for complex diseases.

Objective. Osteoarthritis (OA), characterized by late-onset degeneration of articular cartilage, is recognized to have a genetic component. We examined the role of 26 single-nucleotide polymorphisms (SNPs) from 24 candidate genes in OA susceptibility and progression.Methods. We compared human complementary DNA libraries from OA-affected and normal cartilage and synovium and selected 22 genes in addition to the estrogen receptor ␣ and vitamin D receptor genes. Based on the availability of polymorphisms, we proceeded to test whether genetic variation at those genes affected susceptibility to or progression of radiographic knee OA over a 10-year period in 749 women (mean age 64 years) from the longitudinal Chingford Study.Results. After adjusting for age and body mass index, we observed significant associations at ADAM12, BMP2, CD36, COX2, and NCOR2 with 3 OA susceptibility traits (presence/absence of joint space narrowing [JSN], presence/absence of osteophytes, and Kellgren/ Lawrence [K/L] score). For the OA progression traits (change over 10 years in the K/L score, osteophyte grade, and JSN grade), we found significant associations with ADAM12, CILP, OPG, and TNA. Overall, we observed 15 associations with nominal significance (P < 0.05) and, by permutation analysis, found that such a number would be observed by chance only 3.8% of the time. Although these tests require replication, the stronger genetic associations observed are unlikely to be attributable simply to multiple comparisons.Conclusion. Our results suggest that OA severity and progression have a multigenic and feature-specific nature. These findings should encourage the development of genetic diagnostics for OA progression based on multiple SNPs and help unravel some of the complex disease mechanisms in OA.

The use of DNA variants in the mapping of the human genome and in the positional cloning of monogenic disease genes is well established. Determining the genetic bases of the more common "multifactorial" diseases, however, presents a major challenge. The genetics of these diseases are complicated by the interplay between many genes and the environment. These investigations will require large numbers of DNA markers and the technology to screen large populations with these markers. The systematic identification of the common DNA polymorphisms in the human genome coupled with the development of high throughput screening methods should allow ultimately the elucidation of the genetic component of most clinical and nonclinical phenotypes.