Soumitra Ghosh

Metabolic defects in lean nondiabetic offspring of NIDDM parents: a cross-sectional study.

First-degree relatives of NIDDM patients have an approximately 40% lifetime risk of developing diabetes, and insulin resistance is the best predictor. However, insulin resistance is altered by many other factors, including age, diet, exercise, and medications. To investigate the metabolic and endocrine alterations associated with insulin resistance when all the above confounding factors are excluded, we examined the first phase of insulin secretion and insulin sensitivity in 49 white normoglycemic (4.99 +/- 0.51 vs. 4.95 +/- 0.41 mmol/l) nonexercising lean (BMI, 24 +/- 3 vs. 23 +/- 2 kg/m2; 105 +/- 3 vs. 104 +/- 3% of ideal body weight) offspring of NIDDM patients. These subjects were compared with 29 matched healthy control subjects by means of an intravenous glucose bolus (0.3 g/kg body wt), immediately followed by a euglycemic-hyperinsulinemic (approximately 420 pmol/l) clamp, along with lipid and amino acid profiles. The offspring showed fasting hyperinsulinemia (40.6 +/- 15.8 vs. 30.9 +/- 13.6 pmol/l; P = 0.005) and higher free fatty acid (FFA) levels (582 +/- 189 vs. 470 +/- 140 micromol; P = 0.007), whereas triglycerides, total cholesterol, and HDL and LDL cholesterol levels were comparable with those of control subjects. Alanine (320 +/- 70 vs. 361 +/- 73 micromol/l; P = 0.017), serine (P = 0.05), and glutamine and glycine (P = 0.02) were lower in the offspring than in the control subjects, whereas branched-chain amino acids (343 +/- 54 vs. 357 +/- 54 micromol/l; P = 0.28) were not different. Insulin sensitivity was lower (4.86 +/- 1.65 vs. 6.17 +/ 1.56 mg x kg(-1) x min(-1); P = 0.001), and an inverse correlation with fasting FFAs in the offspring (adjusted R2 = 0.21, P = 0.0005), but not in control subjects (adjusted R2 = 0.03, P = 0.368), was found. Because insulin sensitivity in the offspring appeared to be a mixture of three distributions, they were subdivided into three subgroups: very low, low, and normal insulin sensitivity (20, 47, and 33%, respectively). The same alterations in amino acid and FFA metabolism were observed in the very low and low subgroups but not in the normal subgroup. The first phase of insulin secretion appeared to compensate significantly for insulin resistance in the low subgroup versus the normal subgroup and controls, but was inappropriately low in the subgroup with very low insulin sensitivity considering its degree of insulin resistance. In conclusion, lean insulin-resistant offspring of NIDDM parents showed 1) trimodal distribution of insulin sensitivity, 2) high fasting plasma FFA concentrations, 3) an inverse correlation between insulin sensitivity and FFA concentration, 4) low plasma gluconeogenic amino acid concentrations, and 5) defective insulin secretion when related to insulin sensitivity in the subgroup of very resistant offspring. These results suggest that, in this white population, insulin sensitivity may be determined by a single major gene and that alterations in FFA metabolism may play a role in the pathogenesis of NIDDM.

The Finland-United States investigation of non-insulin-dependent diabetes mellitus genetics (FUSION) study. I. An autosomal genome scan for genes that predispose to type 2 diabetes

We performed a genome scan at an average resolution of 8 cM in 719 Finnish sib pairs with type 2 diabetes. Our strongest results are for chromosome 20, where we observe a weighted maximum LOD score (MLS) of 2.15 at map position 69.5 cM from pter and secondary weighted LOD-score peaks of 2.04 at 56.5 cM and 1.99 at 17.5 cM. Our next largest MLS is for chromosome 11 (MLS = 1.75 at 84.0 cM), followed by chromosomes 2 (MLS = 0.87 at 5.5 cM), 10 (MLS = 0.77 at 75.0 cM), and 6 (MLS = 0.61 at 112.5 cM), all under an additive model. When we condition on chromosome 2 at 8.5 cM, the MLS for chromosome 20 increases to 5.50 at 69.0 cM (P=.0014). An ordered-subsets analysis based on families with high or low diabetes-related quantitative traits yielded results that support the possible existence of disease-predisposing genes on chromosomes 6 and 10. Genomewide linkage-disequilibrium analysis using microsatellite marker data revealed strong evidence of association for D22S423 (P=.00007). Further analyses are being carried out to confirm and to refine the location of these putative diabetes-predisposing genes.

The Finland-United States investigation of non-insulin-dependent diabetes mellitus genetics (FUSION) study. II. An autosomal genome scan for diabetes-related quantitative-trait loci

Type 2 diabetes mellitus is a complex disorder encompassing multiple metabolic defects. We report results from an autosomal genome scan for type 2 diabetes-related quantitative traits in 580 Finnish families ascertained for an affected sibling pair and analyzed by the variance components-based quantitative-trait locus (QTL) linkage approach. We analyzed diabetic and nondiabetic subjects separately, because of the possible impact of disease on the traits of interest. In diabetic individuals, our strongest results were observed on chromosomes 3 (fasting C-peptide/glucose: maximum LOD score [MLS] = 3.13 at 53.0 cM) and 13 (body-mass index: MLS = 3.28 at 5.0 cM). In nondiabetic individuals, the strongest results were observed on chromosomes 10 (acute insulin response: MLS = 3.11 at 21.0 cM), 13 (2-h insulin: MLS = 2.86 at 65.5 cM), and 17 (fasting insulin/glucose ratio: MLS = 3.20 at 9.0 cM). In several cases, there was evidence for overlapping signals between diabetic and nondiabetic individuals; therefore we performed joint analyses. In these joint analyses, we observed strong signals for chromosomes 3 (body-mass index: MLS = 3.43 at 59.5 cM), 17 (empirical insulin-resistance index: MLS = 3.61 at 0.0 cM), and 19 (empirical insulin-resistance index: MLS = 2.80 at 74.5 cM). Integrating genome-scan results from the companion article by Ghosh et al., we identify several regions that may harbor susceptibility genes for type 2 diabetes in the Finnish population.

Familiality of Quantitative Metabolic Traits in Finnish Families with Non-Insulin-Dependent Diabetes mellitus

Type 2 diabetes mellitus (NIDDM) is a complex disorder encompassing multiple metabolic defects. There exists strong evidence for a genetic component to NIDDM; however, to date there have been few reports of linkage between genetic markers along the genome and NIDDM or NIDDM-related quantitative traits. We sought to determine whether individual quantitative traits which determine glucose tolerance exhibit familiality in Finnish families with at least one NIDDM-affected sibling pair. Tolbutamide-modified frequently sampled intravenous glucose tolerance tests (FSIGT) were performed on unaffected offspring (n = 431) and spouses (n = 154) of affected sibling pairs sampled for the Finland-United States Investigation of NIDDM Genetics (FUSION) study. FSIGT data were analyzed using the Minimal Model to obtain quantitative measures of insulin sensitivity (SI), glucose effectiveness (SG), and insulin secretion assessed as the acute insulin response to glucose (AIR). The disposition index (DI), a measure of insulin resistance-corrected β-cell function, was also derived as the product of SI and AIR. Variance components analysis was used to determine for each trait, the heritability (h2), the proportion of the total trait variance accounted for by additive genes. After adjustment for age, gender, and body mass index, h2 estimates were: SG: 18 ± 9%, SI: 28 ± 8%, AIR: 35 ± 8%, and DI: 23 ± 8%. We conclude that there is strong evidence for modest heritability of Minimal-Model-derived NIDDM-related quantitative traits in unaffected spouses and offspring of Finnish affected sibling pairs.

Genetic Analysis of NIDDM: The Study of Quantitative Traits

Many studies are in progress worldwide to elucidate the genetics of NIDDM. Nevertheless, few articles are available that combine the interdisciplinary fields of medicine, genetics, physiology, and statistics in order to provide the scientific rationale for such an endeavor. Here we describe the methodology and background necessary to study the genetics of NIDDM and discuss how to analyze the data. We also provide a detailed bibliography for researchers and a glossary for those who are not experts in the field. In particular, we wish to emphasize the analysis of intermediate quantitative traits as a means to dissect the genetic basis of NIDDM.

Mapping Genes for NIDDM: Design of the Finland—United States Investigation of NIDDM Genetics (FUSION) Study

OBJECTIVE To map and identify susceptibility genes for NIDDM and for the intermediate quantitative traits associated with NIDDM. RESEARCH DESIGN AND METHODS We describe the methodology and sample of the Finland-United States Investigation of NIDDM Genetics (FUSION) study. The whole genome search approach is being applied in studies of several different ethnic groups to locate susceptibility genes for NIDDM. Detailed description of the study materials and designs of such studies are important, particularly when comparing the findings in these studies and when combining different data sets. RESULTS Using a careful selection strategy, we have ascertained 495 families with confirmed NIDDM in at least two siblings and no history of IDDM among the first-degree relatives. These families were chosen from more than 22,000 NIDDM patients, representative of patients with NIDDM in the Finnish population. In a subset of families, a spouse and offspring were sampled, and they participated in a frequently sampled intravenous glucose tolerance test (FSIGT) analyzed with the Minimal Model. An FSIGT was completed successfully for at least two nondiabetic offspring in 156 families with a confirmed nondiabetic spouse and no history of IDDM in first-degree relatives. CONCLUSIONS Our work demonstrates the feasibility of collecting a large number of affected sib-pair families with NIDDM to provide data that will enable a whole genome search approach, including linkage analysis.

Power of variance component linkage analysis to detect epistasis

Variance component methods are now being used in linkage analysis to detect genes influencing complex diseases. These methods are easily extended to allow for simultaneous estimation of both the additive effects of multiple loci on phenotypic variation (conditional oligogenic analysis) and the additive interaction (epistatic) effects among loci. We performed linkage analyses on 200 of the simulated replicates in order to evaluate the power to detect the main effects of MG1and MG2 on Q1 as well as their interaction effects. The power to detect the main effect of MG1 was moderately good, although the power to detect MG2 and the MG1×MG2 interaction was poor.

Identification of a novel inflammation-protective locus in the Fischer rat

Abstract. Inbred LEW/N rats are relatively susceptible, while histocompatible inbred F344/N rats are relatively resistant to development of a wide variety of inflammatory diseases in response to a range of pro-inflammatory stimuli. In a LEW/N vs. F344/N F2 intercross, we identified a quantitative trait locus (QTL) on Chr 10 that protects in a dominant fashion against the exudate volume component of innate inflammation in the F344/N rat, as well as a suggestive QTL on Chr 2 near the Fibrinogen cluster region. The exudate volume linkage region on Chr 10 may be similar to one of the multiple regions found to link to inflammatory arthritis phenotypes in other crosses. The suggestive linkage on Chr 2 has not been previously reported and does not seem to contribute to this phenotype in the same manner as the QTL on Chr 10. These findings are consistent with the hypothesis that the innate exudate volume trait is a sub-phenotype of more complex inflammatory phenotypes, such as arthritis, and genes within the Chr 10 linkage region could account for differences in this non-specific acute phase component of the inflammatory response. Since the rat Chr 10 exudate volume linkage region we have identified is syntenic with a region of human Chr 17 that has been shown to link to a variety of autoimmune/inflammatory diseases, including insulin-dependent diabetes mellitus, multiple sclerosis, and psoriasis, identification of genes within this linkage region will shed light on genes relevant to the earliest inflammatory component and to susceptibility and resistance to such human autoimmune/inflammatory diseases.

A large sample of finnish diabetic sib-pairs reveals no evidence for a non-insulin-dependent diabetes mellitus susceptibility locus at 2qter.

In the first reported positive result from a genome scan for non-insulin-dependent diabetes mellitus (NIDDM), Hanis et al. found significant evidence of linkage for NIDDM on chromosome 2q37 and named the putative disease locus NIDDM1 (Hanis et al. 1996. Nat. Genet. 13:161-166). Their total sample was comprised of 440 Mexican-American affected sib-pairs from 246 sibships. The strongest evidence for linkage was at marker D2S125 and best estimates of lambdas (risk to siblings of probands/population prevalence) using this marker were 1.37 under an additive model and 1.36 under a multiplicative model. We examined this chromosomal region using linkage analysis in a Finnish sample comprised of 709 affected sib-pairs from 472 sibships. We excluded this region in our sample (multipoint logarithm of odds score </= -2) for lambdas >/= 1.37. We discuss possible reasons why linkage to 2q37 was not found and conclude that this region is unlikely to be playing a major role in NIDDM susceptibility in the Finnish Caucasian population.

Complete maternal isodisomy of chromosome 8 in an individual with an early-onset ileal carcinoid tumor

Uniparental disomy (UPD) is a condition in which diploid individuals possess a chromosome pair from a single parent. In some instances, UPD causes an abnormal phenotype due to imprinting effects, reduction to homozygosity at recessive disease loci, or trisomy mosaicism. Here we report the first account of an individual with apparently nonmosaic complete maternal isodisomy of chromosome 8. This individual was identified during routine genotyping in a genomewide search for type 2 diabetes susceptibility genes, although he does not have diabetes. He is of normal appearance, stature, and intelligence, but there is an unusual history of early onset ileal carcinoid. The discovery of other maternal UPD 8 cases will be necessary to define whether this condition causes a distinct phenotype.