Association of the calpain-10 gene with type 2 diabetes mellitus in a Mexican population

Genetic susceptibility to pre diabetes mellitus and related association with obesity and physical fitness components in Mexican-Mestizos

Pre diabetes mellitus (pre-DM) is considered an early-reversible condition that can progress to Type 2 diabetes mellitus (T2DM) which is the main cause of death for adult Mexican population. Gene variants influencing fasting glucose levels may constitute helpful tool for prevention purposes in pre-DM condition. Physically active Mexican-Mestizo adults (n=565) were genotyped for 6 single nucleotide polymorphisms (SNPs) (ADIPOQ rs2241766, ACSL1 rs9997745, LIPC rs1800588, PPARA rs1800206, PPARG rs1801282 and PPARGC1A rs8192678) related to lipid and carbohydrate metabolism. Fasting glucose was measured and values classified as pre-DM (≥100mg/dL) or normal fasting glucose. Logistic models were used to test associations between pre-DM condition and SNPs, and interaction with Body Mass Index (BMI) and physical fitness components. The A allele of ASCL1 rs9997745 conferred increased risk (OR=3.39, p=0.001) of pre-DM which is modulated by BMI. The A allele of the PPARGC1A rs8192678 showed significant SNP*BMI (OR=1.10, p=0.008) interaction effect for pre-DM risk, meaning that obese subjects showed higher pre-DM risk but normal weight subjects showed lower risk. The effect increased with age and was attenuated by higher cardiorespiratory values. We found that both ACSL1 rs9997745 and PPARGC1A rs8192678 are associated with pre-DM, and that BMI significantly modified their association.

Calpain-10 and Adiponectin Gene Polymorphisms in Korean Type 2 Diabetes Patients

BACKGROUND

Genetic variations in calpain-10 and adiponectin gene are known to influence insulin secretion and resistance in type 2 diabetes mellitus. Recently, several single nucleotide polymorphisms (SNPs) in calpain-10 and adiponectin gene have been reported to be associated with type 2 diabetes and various metabolic derangements. We investigated the associations between specific calpain-10 and adiponectin gene polymorphisms and Korean type 2 diabetes patients.

METHODS

Overall, 249 type 2 diabetes patients and 131 non-diabetic control subjects were enrolled in this study. All the subjects were genotyped for SNP-43 and -63 of calpain-10 gene and G276T and T45G frequencies of the adiponectin gene. The clinical characteristics and measure of glucose metabolism were compared within these genotypes.

RESULTS

Among calpain-10 polymorphisms, SNP-63 T/T were more frequent in diabetes patients, and single SNP-63 increases the susceptibility to type 2 diabetes. However, SNP-43 in calpain-10 and T45G and intron G276T in adiponectin gene were not significantly associated with diabetes, insulin resistance, nor insulin secretion.

CONCLUSION

Variations in calpain-10, SNP-63 seems to increase the susceptibility to type 2 diabetes in Koreans while SNP-43 and adiponectin SNP-45, -276 are not associated with impaired glucose metabolism.

Calpain Inhibition Attenuates Adipose Tissue Inflammation and Fibrosis in Diet-induced Obese Mice

Adipose tissue macrophages have been proposed as a link between obesity and insulin resistance. However, the mechanisms underlying these processes are not completely defined. Calpains are calcium-dependent neutral cysteine proteases that modulate cellular function and have been implicated in various inflammatory diseases. To define whether activated calpains influence diet-induced obesity and adipose tissue macrophage accumulation, mice that were either wild type (WT) or overexpressing calpastatin (CAST Tg), the endogenous inhibitor of calpains were fed with high (60% kcal) fat diet for 16 weeks. CAST overexpression did not influence high fat diet-induced body weight and fat mass gain throughout the study. Calpain inhibition showed a transient improvement in glucose tolerance at 5 weeks of HFD whereas it lost this effect on glucose and insulin tolerance at 16 weeks HFD in obese mice. However, CAST overexpression significantly reduced adipocyte apoptosis, adipose tissue collagen and macrophage accumulation as detected by TUNEL, Picro Sirius and F4/80 immunostaining, respectively. CAST overexpression significantly attenuated obesity-induced inflammatory responses in adipose tissue. Furthermore, calpain inhibition suppressed macrophage migration to adipose tissue in vitro. The present study demonstrates a pivotal role for calpains in mediating HFD-induced adipose tissue remodeling by influencing multiple functions including apoptosis, fibrosis and inflammation.

Genetic Epidemiology of Type 2 Diabetes in Mexican Mestizos

There are currently about 415 million people with diabetes worldwide, a figure likely to increase to 642 million by 2040. In 2015, Mexico was the second Latin American country and sixth in the world in prevalence of this disorder with nearly 11.5 million of patients. Type 2 diabetes (T2D) is the main kind of diabetes and its etiology is complex with environmental and genetic factors involved. Indeed, polymorphisms in several genes have been associated with this disease worldwide. To estimate the genetic epidemiology of T2D in Mexican mestizos a systematic bibliographic search of published articles through PubMed, Scopus, Google Scholar, and Web of Science was conducted. Just case-control studies of candidate genes about T2D in Mexican mestizo inhabitants were included. Nineteen studies that met the inclusion criteria were found. In total, 68 polymorphisms of 41 genes were assessed; 26 of them were associated with T2D risk, which were located in ABCA1, ADRB3, CAPN10, CDC123/CAMK1D, CDKAL1, CDKN2A/2B, CRP, ELMO1, FTO, HHEX, IGF2BP2, IRS1, JAZF1, KCNQ1, LOC387761, LTA, NXPH1, SIRT1, SLC30A8, TCF7L2, and TNF-α genes. Overall, 21 of the 41 analyzed genes were associated with T2D in Mexican mestizos. Such a genetic heterogeneity compares with findings in other ethnic groups.

Role of the calpain on the development of diabetes mellitus and its chronic complications

Diabetes mellitus (DM) is associated with acute and chronic complications that cause major morbidity and significant mortality. Calpains, a family of Ca(2+)-dependent cytosolic cysteine proteases, can modulate their substrates' structure and function through limited proteolytic activity. Calpain is a ubiquitous calcium-sensitive protease that is essential for normal physiologic function. However, alterations in calcium homeostasis lead to pathologic activation of calpain in diabetes mellitus. Since not much is known on the relationship between calpain and diabetes mellitus, this review outlines the contribution of calpain to chronic complications of diabetes mellitus, such as diabetic cardiomyopathy, diabetic nephropathy and diabetic retinopathy.

Role of calpain-10 in the development of diabetes mellitus and its complications

Calpain activity has been implicated in several cellular processes such as cell signaling, apoptosis, exocytosis, mitochondrial metabolism and cytoskeletal remodeling. Evidence has indicated that the impairment of calpain expression and the activity of different calpain family members are involved in diverse pathologies. Calpain-10 has been implicated in the development of type 2 diabetes, and polymorphisms in the CAPN10 gene have been associated with an increased risk of developing this disease. The present work focused on the molecular biology of calpain-10, supporting its key participation in glucose metabolism. Current knowledge regarding the role of calpain-10 in the development of type 2 diabetes mellitus and diabetes-related diseases is additionally reviewed.

Arsenic exposure and calpain-10 polymorphisms impair the function of pancreatic beta-cells in humans: a pilot study of risk factors for T2DM

The incidence of type 2 diabetes mellitus (T2DM) is increasing worldwide and diverse environmental and genetic risk factors are well recognized. Single nucleotide polymorphisms (SNPs) in the calpain-10 gene (CAPN-10), which encodes a protein involved in the secretion and action of insulin, and chronic exposure to inorganic arsenic (iAs) through drinking water have been independently associated with an increase in the risk for T2DM. In the present work we evaluated if CAPN-10 SNPs and iAs exposure jointly contribute to the outcome of T2DM. Insulin secretion (beta-cell function) and insulin sensitivity were evaluated indirectly through validated indexes (HOMA2) in subjects with and without T2DM who have been exposed to a gradient of iAs in their drinking water in northern Mexico. The results were analyzed taking into account the presence of the risk factor SNPs SNP-43 and -44 in CAPN-10. Subjects with T2DM had significantly lower beta-cell function and insulin sensitivity. An inverse association was found between beta-cell function and iAs exposure, the association being more pronounced in subjects with T2DM. Subjects without T2DM who were carriers of the at-risk genotype SNP-43 or -44, also had significantly lower beta-cell function. The association of SNP-43 with beta-cell function was dependent on iAs exposure, age, gender and BMI, whereas the association with SNP-44 was independent of all of these factors. Chronic exposure to iAs seems to be a risk factor for T2DM in humans through the reduction of beta-cell function, with an enhanced effect seen in the presence of the at-risk genotype of SNP-43 in CAPN-10. Carriers of CAPN-10 SNP-44 have also shown reduced beta-cell function.

Calpain-10 gene polymorphisms in type 2 diabetes and its micro- and macrovascular complications

Genetic variations in the calpain 10 gene (CAPN10) were previously implicated with increased risk of type 2 diabetes (T2DM). We studied the association of single nucleotide polymorphisms in the CAPN10 gene, SNP -43, SNP -19 and SNP -63, with T2DM and its complications. Overall, we examined 1440 individuals: 880 patients with diabetes and 560 healthy subjects, all Caucasians of Polish origin. All subjects were genotyped for the CAPN10 SNPs by polymerase chain reaction (PCR). The frequencies of alleles, genotypes and haplotypes at three studied loci were similar between the groups. However, the -43 SNP was significantly more frequent in T2DM patients with coexisting cardiovascular disease (CVD) than in patients without CVD (p=0.001). The -43 SNP was still significantly associated with the risk of CVD after adjusting for potential risk factors including male gender, age, BMI, dyslipidemia and hypertension. The odds ratio for G allele for CVD+ versus CVD- patients was 1.89, 95% CI 1.52-2.35. None of the studied SNPs was significantly associated with microvascular diabetic complications. There was a tendency to increased frequency of SNP -43 1/1 homozygotes in patients with diabetic retinopathy (p=0.057). The homozygous haplotype combination 121/121 was more frequent in T2DM patients than in non-diabetic controls (18.4% vs 10.5%, p=0.019). In conclusion, the results of our study suggest the significant association of SNP -43 with the risk of CVD coexisting with T2DM. We also observed that 121/121 haplotype was associated with T2DM in the studied population.

Contribution of common genetic variation to the risk of type 2 diabetes in the Mexican Mestizo population

Several studies have identified nearly 40 different type 2 diabetes susceptibility loci, mainly in European populations, but few of them have been evaluated in the Mexican population. The aim of this study was to examine the extent to which 24 common genetic variants previously associated with type 2 diabetes are associated in Mexican Mestizos. Twenty-four single nucleotide polymorphisms (SNPs) in or near genes (KCNJ11, PPARG, TCF7L2, SLC30A8, HHEX, CDKN2A/2B, CDKAL1, IGF2BP2, ARHGEF11, JAZF1, CDC123/CAMK1D, FTO, TSPAN8/LGR5, KCNQ1, THADA, ADAMTS9, NOTCH2, NXPH1, RORA, UBQLNL, and RALGPS2) were genotyped in Mexican Mestizos. A case-control association study comprising 1,027 type 2 diabetic individuals and 990 control individuals was conducted. To account for population stratification, a panel of 104 ancestry-informative markers was analyzed. Association to type 2 diabetes was found for rs13266634 (SLC30A8), rs7923837 (HHEX), rs10811661 (CDKN2A/2B), rs4402960 (IGF2BP2), rs12779790 (CDC123/CAMK1D), and rs2237892 (KCNQ1). In addition, rs7754840 (CDKAL1) was associated in the nonobese type 2 diabetic subgroup, and for rs7903146 (TCF7L2), association was observed for early-onset type 2 diabetes. Lack of association for the rest of the variants may have resulted from insufficient power to detect smaller allele effects.

Diabetic nephropathy among Mexican Americans

The incidence of diabetic nephropathy (DN) is growing rapidly worldwide as a consequence of the rising prevalence of Type 2 diabetes mellitus (T2DM). Among U.S. ethnic groups, Mexican Americans have a disproportionately high incidence and prevalence of DN and associated end-stage renal disease (ESRD). In communities bordering Mexico, as many as 90% of Mexican American patients with ESRD also suffer from T2DM compared to only 50% of non-Hispanic Whites (NHW). Both socio-economic factors and genetic predisposition appear to have a strong influence on this association. In addition, certain pathogenetic and clinical features of T2DM and DN are different in Mexican Americans compared to NHW, raising questions as to whether the diagnostic and treatment strategies that are standard practice in the NHW patient population may not be applicable in Mexican Americans. This article reviews the epidemiology of DN in Mexican Americans, describes the pathophysiology and associated risk factors, and identifies gaps in our knowledge and understanding that needs to be addressed by future investigations.

A replication study of the IRS1, CAPN10, TCF7L2, and PPARG gene polymorphisms associated with type 2 diabetes in two different populations of Mexico

Type 2 diabetes (T2D) is a chronic degenerative disease that involves the participation of several genetic and environmental factors. The objective of the study was to determine the association of the IRS1 (rs1801278), CAPN10 (rs3792267), TCF7L2 (rs7903146 and rs12255372), and PPARG (rs1801282) gene polymorphisms with T2D, in two different Mexican populations. We conducted a case-control replication study in the state of Guerrero and in Mexico City, with 400 subjects from Guerrero and 1065 from Mexico City. Data were analyzed by logistic regression, adjusting by ancestry, age, gender, and BMI, to determine the association with T2D. Heterozygosity for the Gly972Arg variant of the IRS1 gene showed the strongest association for T2D in both analyzed samples (OR = 2.43, 95% CI 1.12-5.26 and 2.64, 95% CI 1.37-5.10, respectively). In addition, an association of two SNPs of the TCF7L2 gene with T2D was observed in both cities: rs7903146, (for Guerrero OR = 1.98 CI95% 1.02-3.89 and for Mexico OR = 1.94 CI95% 1.31-2.88) and rs12255372 (OR = 1.79 CI95% 1.08-2.97, OR = 1.78 CI95% 1.17-2.71 respectively). We suggest that our results provide strong evidence that variation in the IRS1 and TCF7L2 genes confers susceptibility to T2D in our studied populations.

Variants within the calpain-10 gene and relationships with type 2 diabetes (T2DM) and T2DM-related traits among Tunisian Arabs

BACKGROUND

Common variations in the calpain 10 (CAPN10) gene variants UCSNP-43, UCSNP-19 and UCSNP-63, and the 112/121 diplotype, are associated with an increased risk of type 2 diabetes (T2DM) and T2DM-related traits.

METHODS

The association of UCSNP-43, -19 and -63 CAPN10 SNPs with T2DM was assessed in 917 Tunisian T2DM patients and 748 ethnically matched non-diabetic controls. CAPN10 genotyping was done by PCR-RFLP.

RESULTS

Significant differences in UCSNP-19 MAF, but not UCSNP-43 or -63, and genotype distribution were seen between patients and controls. Heterogeneity in UCSNP-19, but not UCSNP-43 and -63, genotype distribution was noted according to geographical origin. Obesity was associated with UCSNP-19, while raised fasting glucose was associated with UCSNP-63, and increased HDL was associated with UCSNP-43. Enrichment of homozygous UCSNP-19 2/2 was seen in overweight and obese compared with lean patients; logistic-regression analyses demonstrated a positive association of the 2/2 genotype with overweight [P=0.003; OR (95% CI)=2.07 (1.28-3.33)] and obese [P=0.021; OR (95% CI)=1.83 (1.10-3.07)] patients. Of the six CAPN10 haplotypes identified, significant enrichment of only haplotype 111 was seen in T2DM patients [Pc=0.034; OR (95% CI)=1.22 (1.06-1.41)], while the frequency of all identified CAPN10 diplotypes, including the high-risk 112/121, was comparable between patients and controls.

CONCLUSION

While CAPN10 UCSNP-19 SNP and haplotype 111 contribute to the risk of T2DM in Tunisian subjects, no significant association between CAPN10 diplotypes and T2DM was demonstrated.

Common polymorphisms of calpain-10 and the risk of Type 2 Diabetes in a Tunisian Arab population: a case-control study

Background

Genetic variations in the calpain-10 gene (CAPN10), in particular the at-risk diplotype (112/121), were previously implicated with increased risk of type 2 diabetes (T2D).

Methods

We examined the association of CAPN10 UCSNP-43 (rs3792267), UCSNP-19 (rs3842570), and UCSNP-63 (rs5030952) SNPs with T2D in 917 Tunisian T2D patients and 748 non-diabetic controls. CAPN10 genotyping was done by PCR-RFLP.

Results

Enrichment of UCSNP-19 2R (minor) allele and 2R/2R genotype was found in T2D patients; the allele and genotype distribution of UCSNP-43 and UCSNP-63 alleles and genotypes were not significantly different between patient groups and non-diabetic control subjects. Regression analysis demonstrated progressive increases in T2D risk in 3R/2R [OR (95% CI) = 1.35 (1.08 - 1.68)] and 2R/2R [OR (95% CI) = 1.61 (1.20 - 2.18)] genotypes. Of the six haplotypes detected, enrichment of haplotype 111 (UCSNP-43/UCSNP-19/UCSNP-63) was seen in patients (Pc = 0.034); the distribution of the other haplotypes was comparable between patients and control subjects; neither haplotype 211 nor haplotype 212 was observed. Furthermore, the frequency of all CAPN10 diplotypes identified, including the "high-risk diplotype (112/121) reported for Mexican-Americans and Northern Europeans, were comparable between patients and controls.

Conclusions

CAPN10 UCSNP-19 variant, and the 111 haplotype contribute to the risk of T2D in Tunisian subjects; no significant associations between CAPN10 diplotypes and T2D were demonstrated for Tunisians.

The activity of calpains in lymphocytes is glucose-dependent and is decreased in diabetic patients

Calpains are nonlysosomal calcium-dependent cysteine proteases that participate in insulin secretion and action. Polymorphisms in the calpain-10 gene have been shown to increase the risk for type 2 diabetes. Since white blood cells have been used to study glucose homeostasis, the present study was carried to find out if calpains have different activity and/or expression in accessible cells such as lymphocytes of individuals with or without type 2 diabetes. Fasting blood glucose concentration was significantly higher in diabetic subjects, whereas the difference in the activity of calpains evaluated in basal and stimulating extracellular glucose concentration was significantly higher in the lymphocytes from the control group. The mRNA expression of calpain-10 was similar in the lymphocytes of both patients and controls. The protein blots showed four bands that ranged between 75 and 50 kDa; however, no statistical differences were observed in the expression of the calpain-10 isoforms between controls and patients. Data obtained showed that human lymphocytes express calpain-10 mRNA and protein, showing a similar expression between diabetic and control subjects, nevertheless in the diabetic group calpain activity was less glucose-sensitive.

Glucose dysregulation in obese children: predictive, risk, and potential protective factors

OBJECTIVE

The aim of our study was to determine the prevalence of impaired glucose tolerance (IGT) and type 2 diabetes (DM2) in obese children and adolescents of Greek origin and compare our data with pertinent literature findings in an attempt to uncover predictive, risk, and preventive factors.

RESEARCH METHODS AND PROCEDURES

A total of 117 obese children and adolescents 12.1+/-2.7 years old underwent a 2-hour oral glucose tolerance test (OGTT). Insulin resistance (IR) and beta-cell function were estimated using the homeostasis model assessment (HOMA)-IR and the insulinogenic index, respectively.

RESULTS

A total of 17 patients (14.5%) had IGT, and none had DM2. The overall prevalence rates of both IGT and DM2 in our subjects were lower than those reported in a recent multiethnic U.S. study. Nevertheless, the difference between our IGT data and those of the U.S. study was due mostly to the prepubertal subjects (9% vs. 25.4%), whereas no difference was observed in the pubertal population (18% vs. 21%). Fasting glucose, insulin, and HOMA-IR values were not predictive of IGT. The absolute value of insulin at 2 hours of the OGTT combined with the time-integrated glycemia (AUCG) can strongly predict IGT, whereas higher area under the curve for insulin (AUCI) values were found to be protective.

DISCUSSION

In ethnic groups less prone to diabetes development, IGT or DM2 in obese subjects is more likely to develop at puberty than at the prepubertal stage. It is advisable that physicians caring for obese adolescents perform an OGTT for early detection of IGT because HOMA-IR values, although higher in IGT subjects and indicative of IR, cannot predict IGT.

Variation in CAPN10 in relation to type 2 diabetes, obesity and quantitative metabolic traits: studies in 6018 whites

The first type 2 diabetes (T2D) gene to be identified in a genome wide scan followed by positional cloning was CAPN10 encoding the cysteine protease calpain-10. Subsequently, a large number of studies have investigated variation in CAPN10 in relation to T2D. Two CAPN10 single nucleotide polymorphisms (SNPs), the SNP43 (rs3792267) and the SNP44 (rs2975760), have been associated with T2D in some, but not all studies conducted in a wide range of ethnicities. We investigated the two SNPs for association with T2D in a relatively large, homogenous population of Danish whites (n = 1359 T2D cases, n = 4659 normoglycemic and glucose-tolerant control subjects), however, no significant associations of the SNP43 or the SNP44 variant with T2D were found. Neither were the two variants associated with obesity, and no association of either variant with diabetes-related quantitative traits was found in a study involving a population-based sample of 5698 middle-aged subjects. Meta-analyses, however, of the present and previously published studies involving 15,368 (SNP43) or 13,628 (SNP44) subjects yielded odds ratios of 1.09 (95% CI 1.02-1.16, p = 0.007) and 1.15 (1.07-1.23, p = 0.0002), respectively, for association with T2D. In conclusion, in a relatively large study sample of whites we found no consistent evidence of association of the CAPN10 SNP43 or SNP44 with T2D, obesity, or related quantitative traits, although meta-analyses of these two CAPN10 SNPs demonstrated an association with T2D.

Hidden population substructures in an apparently homogeneous population bias association studies

Linkage- and association-based approaches have been applied to attempt to unravel the genetic predisposition for complex diseases. However, studies often report contradictory results even when similar population backgrounds are investigated. Unrecognized population substructures could possibly explain these inconsistencies. In an apparently homogeneous German sample of 612 patients with type 2 diabetic and end-stage diabetic nephropathy and 214 healthy controls, we tested for hidden population substructures and their possible effects on association. Using a genetic vector space analysis of genotypes of 20 microsatellite markers, we identified four distinct subsets of cases and controls. The significance of these substructures was demonstrated by subsequent association analyses, using three genetic markers (UCSNP-43,-19,-63; intron 3 of the calpain-10 gene). In the undivided sample, we found no association between individual SNPs or any haplogenotypes (ie the genotype combination of two multilocus haplotypes) and type 2 diabetes. In contrast, when analyzing the four groups separately, we found that there was evidence for association of the common C allele of UCSNP-63 with the trait in the largest group (n=547 cases/101 controls; P=0.002). In this subset haplotype 112 was more frequent in controls than in cases (P=0.006; haplogenotype 112/121: odds ratio (OR)=0.27, 95% confidence intervals (CI)=0.13-0.57), indicating a protective effect against the development of type 2 diabetes. Our study demonstrates that unconsidered population substructures (ethnicity-dependent factors) can severely bias association studies.

A novel 111/121 diplotype in the Calpain-10 gene is associated with type 2 diabetes

Genetic variations in the Calpain-10 gene, CAPN10, have been reported to be associated with the risk of type 2 diabetes mellitus (T2DM) in Mexican-Americans and Northern Europeans whereas these variations are not associated with T2DM in other populations. The aim of this study was to determine whether there is an association between specific CAPN10 diplotype (SNP-43, -19, and -63) and T2DM in the Korean population. Overall, 454 Korean patients with T2DM (male 230, female 224) and 236 non-diabetic controls (male 124, female 112) with no family history of diabetes were enrolled in this study. All the subjects were genotyped according to CAPN10 SNP-43, -19, and -63. The restriction fragment length polymorphism method was used for the three SNPs. There were eight estimated haplotype allelic variations. After adjusting for gender and age, the 111 haplotype was associated with a high risk of T2DM (P <0.0001). The 111/121 diplotype was associated with a high risk of T2DM (odds ratio =2.580, 95% confidence interval =1.602-4.155, P =0.001). The high-risk haplotype (112/121) in Mexican-Americans was not significant in our study population. In conclusion, we found that a novel 111/121 diplotype in Calpain-10 gene is associated with T2DM in the Korean population.

Genetic epidemiology of diabetes

Conventional genetic analysis focuses on the genes that account for specific phenotypes, while traditional epidemiology is more concerned with the environmental causes and risk factors related to traits. Genetic epidemiology is an alliance of the 2 fields that focuses on both genetics, including allelic variants in different populations, and environment, in order to explain exactly how genes convey effects in different environmental contexts and to arrive at a more complete comprehension of the etiology of complex traits. In this review, we discuss the epidemiology of diabetes and the current understanding of the genetic bases of obesity and diabetes and provide suggestions for accelerated accumulation of clinically useful genetic information.

Calpain 10 and type 2 diabetes: are we getting closer to an explanation?

PURPOSE OF REVIEW

A variation in the gene encoding the cysteine protease calpain 10 (CAPN10) was recently linked and associated with type 2 diabetes by positional cloning. This positional cloning was a follow-up investigation to the identification of a diabetes-linked region on human chromosome 2 identified by genome-wide scanning a few years earlier. In this paper we give a general background on the genetic studies performed on CAPN10 to date, and review the most recent studies on the functional role of calpain 10.

RECENT FINDING

A haplotype or haplotype combination comprising three intronic single nucleotide polymorphisms (UCSNP-43, 19, and 63) were associated with a threefold increased risk of type 2 diabetes in the population in which linkage was first found. Another polymorphism, UCSNP-44, which is in linkage disequilibrium with a coding single-nucleotide polymorphism (Thr504Ala), has subsequently been associated with type 2 diabetes in extensive meta-analyses. Meanwhile, initial studies probing the possible role of calpain-10, completely unknown at the time, are now being pursued, both in isolated cells and humans.

SUMMARY

The positional cloning of CAPN10 as a candidate gene for type 2 diabetes has been particularly fruitful. Not only has it identified an important and surprising piece of the puzzle underlying the development of diabetes, but it has also modelled and paved the way for investigations concerning complex genetic diseases other than type 2 diabetes.

[Genetics of type 2 diabetes]

In the last years type 2 diabetes has reached almost epidemic proportions. More than 170 million individuals are affected worldwide, about 6 million in Germany. Manifestation of type 2 diabetes is determined by both environmental factors such as lack of physical exercise and overeating and a genetic predisposition. Despite enormous efforts in medical research to identify susceptibility loci and high risk alleles, the genetics of common type 2 diabetes (non-MODY) remain unknown. To date, only a few susceptibility genes have been identified (such as PPARG, KCNJ11, CAPN10). However, replication of initial studies is often difficult. This can be explained by both locus and allelic heterogeneity as well as ethnic differences between different populations. Studies in genetically isolated populations such as the Pima Indians are advantageous to identify susceptibility alleles. Despite some recent advances, it is not possible to predict an individual's risk of type 2 diabetes based on the presence of a certain disease-risk allele.

Genetics of Type 2 diabetes

Type 2 diabetes (T2D) has become a health-care problem worldwide, with the rise in disease prevalence being all the more worrying as it not only affects the developed world but also developing nations with fewer resources to cope with yet another major disease burden. Furthermore, the problem is no longer restricted to the ageing population, as young adults and children are also being diagnosed with T2D. In recent years, there has been a surge in the number of genetic studies of T2D in attempts to identify some of the underlying risk factors. In this review, I highlight the main genes known to cause uncommon monogenic forms of diabetes (e.g. maturity-onset diabetes of the young--MODY--and insulin resistance syndromes), as well as describe some of the main approaches used to identify genes involved in the more common forms of T2D that result from the interaction between environmental risk factors and predisposing genotypes. Linkage and candidate gene studies have been highly successful in the identification of genes that cause the monogenic variants of diabetes and, although progress in the more common forms of T2D has been slow, a number of genes have now been reproducibly associated with T2D risk in multiple studies. These are discussed, as well as the main implications that the diabetes gene discoveries will have in diabetes treatment and prevention.

Genes and Type 2 Diabetes Mellitus

Type 2 diabetes (T2DM) comprises a group of entities with different genetic causes. In most patients, T2DM results from alterations of various genes, each having a partial and additive effect. The inheritance pattern is thus complex, and environmental factors play an important role in favoring or delaying the expression of the disease. The identification of susceptibility genes and genetic variants requires different methodological approaches. Here we address some of the most important strategies and findings on the genomic basis of T2DM, as well as evidence of genetic heterogeneity among populations. The identification of the underlying genetic causes of T2DM and other related traits such as obesity and hypertension will lead to the development of new therapeutic targets likely to impact the way we treat these diseases. Survival and quality of life for T2DM patients is expected to eventually increase, significantly lessening the socioeconomic burden of the disease.

Type 2 diabetes: principles of pathogenesis and therapy

Type 2 diabetes mellitus has become an epidemic, and virtually no physician is without patients who have the disease. Whereas insulin insensitivity is an early phenomenon partly related to obesity, pancreas beta-cell function declines gradually over time already before the onset of clinical hyperglycaemia. Several mechanisms have been proposed, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction for insulin resistance, and glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, but only a handful of genes have been identified so far: genes for calpain 10, potassium inward-rectifier 6.2, peroxisome proliferator-activated receptor gamma, insulin receptor substrate-1, and others. Management includes not only diet and exercise, but also combinations of anti-hyperglycaemic drug treatment with lipid-lowering, antihypertensive, and anti platelet therapy.