Are variants in the CAPN10 gene related to risk of type 2 diabetes? A quantitative assessment of population and family-based association studies

Partners in diabetes epidemic: A global perspective

There is a recent increase in the worldwide prevalence of both obesity and diabetes. In this review we assessed insulin signaling, genetics, environment, lipid metabolism dysfunction and mitochondria as the major determinants in diabetes and to identify the potential mechanism of gut microbiota in diabetes diseases. We searched relevant articles, which have key information from laboratory experiments, epidemiological evidence, clinical trials, experimental models, meta-analysis and review articles, in PubMed, MEDLINE, EMBASE, Google scholars and Cochrane Controlled Trial Database. We selected 144 full-length articles that met our inclusion and exclusion criteria for complete assessment. We have briefly discussed these associations, challenges, and the need for further research to manage and treat diabetes more efficiently. Diabetes involves the complex network of physiological dysfunction that can be attributed to insulin signaling, genetics, environment, obesity, mitochondria and stress. In recent years, there are intriguing findings regarding gut microbiome as the important regulator of diabetes. Valid approaches are necessary for speeding medical advances but we should find a solution sooner given the burden of the metabolic disorder - What we need is a collaborative venture that may involve laboratories both in academia and industries for the scientific progress and its application for the diabetes control.

Genetics of diabetes

Diabetes mellitus is a complicated disease characterized by a complex interplay of genetic, epigenetic, and environmental variables. It is one of the world's fastest-growing diseases, with 783 million adults expected to be affected by 2045. Devastating macrovascular consequences (cerebrovascular disease, cardiovascular disease, and peripheral vascular disease) and microvascular complications (like retinopathy, nephropathy, and neuropathy) increase mortality, blindness, kidney failure, and overall quality of life in individuals with diabetes. Clinical risk factors and glycemic management alone cannot predict the development of vascular problems; multiple genetic investigations have revealed a clear hereditary component to both diabetes and its related complications. In the twenty-first century, technological advancements (genome-wide association studies, next-generation sequencing, and exome-sequencing) have led to the identification of genetic variants associated with diabetes, however, these variants can only explain a small proportion of the total heritability of the condition. In this review, we address some of the likely explanations for this "missing heritability", for diabetes such as the significance of uncommon variants, gene-environment interactions, and epigenetics. Current discoveries clinical value, management of diabetes, and future research directions are also discussed.

Identification of DNA methylation of CAPN10 gene changes in the patients with type 2 diabetes mellitus as a predictive biomarker instead of HbA1c, random blood sugar, lipid profile, kidney function test, and some risk factors

Objective. Nowadays, type 2 diabetes mellitus (T2DM) is the most common chronic endocrine disorder, affecting an estimated 5-10% of adults worldwide and this disease rapidly increases in the Kurdistan region population. This research aims to identify DNA methylation change in the CPAN10 gene as a predictive biomarker in T2DM and the association between DNA methylation status with lipid profile and kidney function test. Methods. The participants (113) were divided into three groups: diabetes group (47), prediabetes group (36), and control group (30). The study was carried out on patients who visited the private clinical sectors between August and December 2021 in the Koya city Kurdistan region of Iraq. To determine DNA methylation status, methylation-specific PCR (MPS) with paired primer for each methylated and unmethylated region was used. The Mann-Whitney U test and Spearman's correlation were performed for statistical analysis of data and a value of p<0.05 was considered significant. Results. The obtained results show that DNA hypermethylation was recorded in the promoter region in the samples of the diabetes and prediabetes groups compared to the healthy group (control). Various factors also affected the level of DNA methylation, such as HbA1c in prediabetes group and body mass index in the control group. Conclusion. These results indicate that DNA methylation changes in the CAPN10 gene promoter region may be used as a potential predictive biomarker to diagnose T2DM; however, this study requires further data to support this evidence.

The Importance of Precision Medicine in Type 2 Diabetes Mellitus (T2DM): From Pharmacogenetic and Pharmacoepigenetic Aspects

BACKGROUND

Type 2 Diabetes Mellitus (T2DM) is a worldwide disorder as the most important challenges of health-care systems. Controlling the normal glycaemia greatly profit long-term prognosis and gives explanation for early, effective, constant, and safe intervention.

MATERIAL AND METHODS

Finding the main genetic and epigenetic profile of T2DM and the exact molecular targets of T2DM medications can shed light on its personalized management. The comprehensive information of T2DM was earned through the genome-wide association study (GWAS) studies. In the current review, we represent the most important candidate genes of T2DM like CAPN10, TCF7L2, PPAR-γ, IRSs, KCNJ11, WFS1, and HNF homeoboxes. Different genetic variations of a candidate gene can predict the efficacy of T2DM personalized strategy medication.

RESULTS

SLCs and AMPK variations are considered for metformin, CYP2C9, KATP channel, CDKAL1, CDKN2A/2B and KCNQ1 for sulphonylureas, OATP1B, and KCNQ1 for repaglinide and the last but not the least ADIPOQ, PPAR-γ, SLC, CYP2C8, and SLCO1B1 for thiazolidinediones response prediction.

CONCLUSION

Taken everything into consideration, there is an extreme need to determine the genetic status of T2DM patients in some known genetic region before planning the medication strategies.

The Play of Genes and Non-genetic Factors on Type 2 Diabetes

Diabetes has been a disease of public health concern for a number of decades. It was in the 1930s when scientists made an interesting discovery that the disease is actually divided into two types as some patients were insensitive to insulin treatment then. Type 2 Diabetes which happens to be the non-insulin dependent one is the most common form of the disease and is caused by the interaction between genetic and non-genetic factors. Despite conflicting results, numerous studies have identified genetic and non-genetic factors associated with this common type of diabetes. This review has summarized literature on some genes and non-genetic factors which have been identified to be associated with Type 2 diabetes. It has sourced literature from PubMed, Web of Science and Medline without any limitation to regions, publication types, or languages. The paper has started with the introduction, the play of non-genetic factors, the impact of genes in general, and ended with the interaction between some genes and environmental factors.

Prenatal exposure to gestational diabetes mellitus increases developmental defects in the enamel of offspring

Background and objective

Gestational diabetes mellitus (GDM) is associated with short- and long-term maternal and perinatal repercussions. Our objective was to evaluate the long-term consequences of intrauterine exposure to hyperglycemia on Developmental Defects of Enamel (DDE) in offspring.

Results

Overall, 50 children of women with GDM and 250 children of normoglycemic women participated, the latter serving as controls. Children were examined at the age between 3 and 12 years. In addition to physical examination, two independent observers examined and rated photographs to identify specific types of DDE in a blinded fashion. Among offspring of mothers with GDM, rates of DDE (all types combined) and hypoplasia (specific type) were significantly higher (p<0.001, p = 0.04), in comparison to offspring of normoglycemic mothers. Considering only the affected teeth (1060 in GDM category; 5499 in controls), rates of DDE (all types combined) were significantly higher for total teeth (p <0.001) and deciduous teeth (p<0.001), but not permanent teeth. In specific types of DDE involving deciduous teeth, rates of demarcate opacity were significantly higher (p<0.001; canine and 2nd mandibular molars) and hypoplasia (p <0.001; 2nd maxillary molars and 2nd mandibular molars). In permanent teeth, the rate of diffuse opacity in association with GDM was significantly higher (p<0.001; maxillary central incisors and 1st maxillary molars).

Conclusion

GDM was associated with the adverse effects of DDE on offspring. This study lays the foundation for future studies to determine the impact of GDM on long-term risk of DDE.

Genetic and Environmental Dispositions for Cardiovascular Variability: A Pilot Study

BACKGROUND

The aim of our study was to evaluate the degree of genetic homozygosity in the group of patients with coronary artery disease (CAD), as well as to evaluate morphogenetic variability in CAD patients regarding the presence of investigated risk factors (RF) compared to a control sample of individuals. Additionally, we aimed to evaluate the distribution of ABO blood type frequencies between tested samples of individuals.

METHODS

This study analyzed individual phenotype and morphogenetic variability of 17 homozygously-recessive characteristics (HRC), by using HRC test in a sample of 148 individuals in CAD patients group and 156 individuals in the control group. The following RF were analyzed: hypertension, diabetes mellitus, hyperlipidemia, and smoking.

RESULTS

The mean value of HRC in CAD patients is significantly higher, while variability decreases compared to the control sample (CAD patients: 4.24 ± 1.59, control sample: 3.75 ± 1.69; V_CAD-patients = 37.50%, V_C = 45.07%). There is a significant difference in individual variations of 17 HRC between control sample and CAD patients (χ² = 169.144; p < 0.01), which points out to different variability for tested genes. Mean values of HRC significantly differed in CAD patients in regard to the number of RF present. A blood type (OR = 1.75) is significant predictor for CAD, while O blood type (OR = 0.43) was significantly associated with controls.

CONCLUSION

There is a higher degree of recessive homozygosity in CAD patients versus individuals in the control sample, and the presence of significant variations in the degree of recessive homozygosity as the number of tested RF increases.

The impact of personalized medicine of Type 2 diabetes mellitus in the global health context

Advances in the fields of genomic sciences have given rise to personalized medicine. This new paradigm draws upon a patient's genetic and metabolic makeup in order to tailor diagnostics and treatment. Personalized medicine holds remarkable promises to improve prevention and management of chronic diseases of global relevance, such as Type 2 diabetes mellitus (T2DM). This review article aims at summarizing the evidence from genome-based sciences on T2DM risk and management in different populations and in the Global Health context. Opinions from leading experts in the field were also included. Based on these findings, strengths and weaknesses of personalized approach to T2DM in a global context are delineated. Implications for future research and implementation on that subject are discussed.

Computational Analysis of Single Nucleotide Polymorphisms Associated with Altered Drug Responsiveness in Type 2 Diabetes

Type 2 diabetes (T2D) is one of the most frequent mortality causes in western countries, with rapidly increasing prevalence. Anti-diabetic drugs are the first therapeutic approach, although many patients develop drug resistance. Most drug responsiveness variability can be explained by genetic causes. Inter-individual variability is principally due to single nucleotide polymorphisms, and differential drug responsiveness has been correlated to alteration in genes involved in drug metabolism (CYP2C9) or insulin signaling (IRS1, ABCC8, KCNJ11 and PPARG). However, most genome-wide association studies did not provide clues about the contribution of DNA variations to impaired drug responsiveness. Thus, characterizing T2D drug responsiveness variants is needed to guide clinicians toward tailored therapeutic approaches. Here, we extensively investigated polymorphisms associated with altered drug response in T2D, predicting their effects in silico. Combining different computational approaches, we focused on the expression pattern of genes correlated to drug resistance and inferred evolutionary conservation of polymorphic residues, computationally predicting the biochemical properties of polymorphic proteins. Using RNA-Sequencing followed by targeted validation, we identified and experimentally confirmed that two nucleotide variations in the CAPN10 gene—currently annotated as intronic—fall within two new transcripts in this locus. Additionally, we found that a Single Nucleotide Polymorphism (SNP), currently reported as intergenic, maps to the intron of a new transcript, harboring CAPN10 and GPR35 genes, which undergoes non-sense mediated decay. Finally, we analyzed variants that fall into non-coding regulatory regions of yet underestimated functional significance, predicting that some of them can potentially affect gene expression and/or post-transcriptional regulation of mRNAs affecting the splicing.

Human-specific derived alleles of CD33 and other genes protect against postreproductive cognitive decline

The individuals of most vertebrate species die when they can no longer reproduce. Humans are a rare exception, having evolved a prolonged postreproductive lifespan. Elders contribute to cooperative offspring care, assist in foraging, and communicate important ecological and cultural knowledge, increasing the survival of younger individuals. Age-related deterioration of cognitive capacity in humans compromises these benefits and also burdens the group with socially costly members. We investigated the contribution of the immunoregulatory receptor CD33 to a uniquely human postreproductive disease, Alzheimer's dementia. Surprisingly, even though selection at advanced age is expected to be weak, a CD33 allele protective against Alzheimer's disease is derived and unique to humans and favors a functional molecular state of CD33 resembling that of the chimpanzee. Thus, derived alleles may be compensatory and restore interactions altered as a consequence of human-specific brain evolution. We found several other examples of derived alleles at other human loci that protect against age-related cognitive deterioration arising from neurodegenerative disease or cerebrovascular insufficiency. Selection by inclusive fitness may be strong enough to favor alleles protecting specifically against cognitive decline in postreproductive humans. Such selection would operate by maximizing the contributions of postreproductive individuals to the fitness of younger kin.

CAPN10 SNP43 G>A gene polymorphism and type 2 diabetes mellitus in the Asian population: a meta-analysis of 9353 participants

A correlation between the single nucleotide polymorphism (SNP)43 G>A in the calpain-10 (CAPN10) gene (i.e., CAPN10 SNP43) and type 2 diabetes mellitus (T2DM) susceptibility has been suggested, but the evidence for such a relationship remains controversial. To explore the association of the CAPN10 SNP43 with T2DM in Asian populations, a meta-analysis including 9,353 participants from 20 individual studies in Asian populations was conducted. The pooled odds ratios (ORs) and their corresponding 95% confidence intervals (95% CIs) were evaluated by a fixed-effect model or random-effect model. The relationship between CAPN10 SNP43 and T2DM was significant under allelic (OR: 1.18, 95% CI: 1.01-1.38, P = 0.03), recessive (OR: 1.236, 95% CI: 1.038-1.472, P =0.017), heterozygous (OR: 1.261, 95% CI: 1.053-1.512, P = 0.012), and additive (OR: 1.183, 95% CI: 1.014-1.381, P = 0.033) genetic models but not under dominant (OR: 1.12, 95% CI: 0.78-1.62, P = 0.53) or homozygous (OR: 0.937, 95% CI: 0.648-1.355, P = 0.730) genetic models. CAPN10 SNP43 was significantly associated with T2DM susceptibility in Asian populations, especially in Chinese populations. Asians, particularly Chinese people with the SNP43 G allele of the CAPN10 gene may have an increased risk of developing T2DM.

Association of IRS1, CAPN10, and PPARG gene polymorphisms with type 2 diabetes mellitus in the high-risk population of Hyderabad, India

BACKGROUND

We attempted to validate earlier findings on the nature of the association of the IRS1, CAPN10, and PPARG genes with type 2 diabetes mellitus (T2DM) in the high-risk population of Hyderabad, India.

METHODS

A sample of 1379 subjects (758 T2DM patients, 621 controls) was genotyped for single nucleotide polymorphisms (SNPs) of the IRS1 (rs1801278), CAPN10 (rs3792267, rs5030952), and PPARG (rs1801282) genes.

RESULTS

The allele and genotype frequencies of IRS1 (rs1801278) and CAPN10 (rs3792267) SNPs differed significantly between the patient and control groups. Logistic regression analysis suggested a significant association of these two SNPs (P ≤ 0.007) with T2DM and the strength of association did not alter when adjusted for age, gender, body mass index, and the waist : hip ratio as covariates. The same two SNPs showed significant association in multivariate logistic regression analyses, even after Bonferroni correction for multiple testing, suggesting an independent nature of the role of these genes in the manifestation of T2DM in our population.

CONCLUSIONS

We replicated the significant association of rs1801278 and rs3792267 SNPs of the IRS1 and CAPN10 genes with T2DM in the population of Hyderabad. Despite the known biological significance of the PPARG gene and a sufficient statistical power of the present study, we could not replicate the association of PPARG with T2DM in our high-risk population. Given the vast ethnic, geographic, and genetic heterogeneity of the Indian population, many more studies are needed covering the ethnic and geographic heterogeneity of India to enable identification of an Indian-specific profile of genes associated with T2DM.

Common genetic variants on FOXE1 contributes to thyroid cancer susceptibility: evidence based on 16 studies

Genome-wide association studies have identified polymorphisms at chromosome 9q22.23 as a new thyroid cancer (TC) susceptibility locus in populations of European descent. Since then, the relationship between three common variations (rs965513, rs1867277, and rs71369530) of FOXE1 and TC has been reported in various ethnic groups; however, the results have been inconclusive. To derive a more precise estimation of the relationship as well as to quantify the between-study heterogeneity and potential bias, a meta-analysis including 120,258 individuals from 16 studies was performed. An overall random-effect per-allele odds ratio (OR) of 1.74 (95 % confidence interval (95 % CI), 1.62-1.86, P<10(-5)) and 1.62 (95 % CI, 1.50-1.76, P<10(-5)) was found for the rs965513 and rs1867277 polymorphisms, respectively. In addition, we also detected significant association of FOXE1 polyalanine tract (rs71369530) with TC risk (OR=2.01; 95 % CI, 1.66-2.44, P<10(-5)). Significant associations were also detected under dominant and recessive genetic models. In the subgroup analysis by ethnicity, significantly increased risks were found for the rs965513 polymorphism among Caucasians (OR=1.79; 95 % CI, 1.69-1.91, P<10(-5)) and Asians (OR=1.42; 95 % CI, 1.12-1.81, P=0.004). Ethnicity was identified as a potential source of between-study heterogeneity for rs965513. When stratified by sample size, study design, histological types of TC, and radiation exposure status, significantly increased risks were found for the rs965513 polymorphism. This meta-analysis demonstrated that the three common variations on FOXE1 is a risk factor associated with increased TC susceptibility, but these associations vary in different ethnic populations.

Quantitative assessment of the effect of KCNJ11 gene polymorphism on the risk of type 2 diabetes

To clarify the role of potassium inwardly-rectifying-channel, subfamily-J, member 11 (KCNJ11) variation in susceptibility to type 2 diabetes (T2D), we performed a systematic meta-analysis to investigate the association between the KCNJ11 E23K polymorphism (rs5219) and the T2D in different genetic models. Databases including PubMed, Medline, EMBASE, and ISI Web of Science were searched to identify relevant studies. A total of 48 published studies involving 56,349 T2D cases, 81,800 controls, and 483 family trios were included in this meta-analysis. Overall, the E23K polymorphism was significantly associated with increased T2D risk with per-allele odds ratio (OR) of 1.12 (95% CI: 1.09-1.16; P<10-5). The summary OR for T2D was 1.09 (95% CI: 1.03-1.14; P<10-5), and 1.26 (95% CI: 1.17-1.35; P<10-5), for heterozygous and homozygous, respectively. Similar results were also detected under dominant and recessive genetic models. When stratified by ethnicity, significantly increased risks were found for the polymorphism in Caucasians and East Asians. However, no such associations were detected among Indian and other ethnic populations. Significant associations were also observed in the stratified analyses according to different mean BMI of cases and sample size. Although significant between study heterogeneity was identified, meta-regression analysis suggested that the BMI of controls significantly correlated with the magnitude of the genetic effect. The current meta-analysis demonstrated that a modest but statistically significant effect of the 23K allele of rs5219 polymorphism in susceptibility to T2D. But the contribution of its genetic variants to the epidemic of T2D in Indian and other ethnic populations appears to be relatively low.

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.

Genetics of diabetes--are we missing the genes or the disease?

Diabetes is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. The chronic hyperglycemia of diabetes is associated with long-term damage, dysfunction, and failure of different organs, especially the eyes, kidneys, nerves, heart, and blood vessels. Several pathogenic processes are involved in the development of diabetes. These range from autoimmune destruction of the beta-cells of the pancreas with consequent insulin deficiency to abnormalities that result in resistance to insulin action (American Diabetes Association, 2011). The vast majority of cases of diabetes fall into two broad categories. In type 1 diabetes (T1D), the cause is an absolute deficiency of insulin secretion, whereas in type 2 diabetes (T2D), the cause is a combination of resistance to insulin action and an inadequate compensatory insulin secretory response. However, the subdivision into two main categories represents a simplification of the real situation, and research during the recent years has shown that the disease is much more heterogeneous than a simple subdivision into two major subtypes assumes. Worldwide prevalence figures estimate that there are 280 million diabetic patients in 2011 and more than 500 million in 2030 (http://www.diabetesatlas.org/). In Europe, about 6-8% of the population suffer from diabetes, of them about 90% has T2D and 10% T1D, thereby making T2D to the fastest increasing disease in Europe and worldwide. This epidemic has been ascribed to a collision between the genes and the environment. While our knowledge about the genes is clearly better for T1D than for T2D given the strong contribution of variation in the HLA region to the risk of T1D, the opposite is the case for T2D, where our knowledge about the environmental triggers (obesity, lack of exercise) is much better than the understanding of the underlying genetic causes. This lack of knowledge about the underlying genetic causes of diabetes is often referred to as missing heritability (Manolio et al., 2009) which exceeds 80% for T2D but less than 25% for T1D. In the following review, we will discuss potential sources of this missing heritability which also includes the possibility that our definition of diabetes and its subgroups is imprecise and thereby making the identification of genetic causes difficult.

Genetics of type 2 diabetes

Type 2 diabetes (T2D) is the result of interaction between environmental factors and a strong hereditary component. We review the heritability of T2D as well as the history of genetic and genomic research in this area. Very few T2D risk genes were identified using candidate gene and linkage-based studies, but the advent of genome-wide association studies has led to the identification of multiple genes, including several that were not previously known to play any role in T2D. Highly replicated genes, for example TCF7L2, KCNQ1 and KCNJ11, are discussed in greater detail. Taken together, the genetic loci discovered to date explain only a small proportion of the observed heritability. We discuss possible explanations for this “missing heritability”, including the role of rare variants, gene-environment interactions and epigenetics. The clinical utility of current findings and avenues of future research are also discussed.

Early-term birth (37-38 weeks) and mortality in young adulthood

BACKGROUND

Early-term birth (gestational age, 37-38 weeks) has been associated with increased infant mortality relative to later-term birth, but mortality beyond infancy has not been studied. We examined the association between early-term birth and mortality through young adulthood.

METHODS

We conducted a national cohort study of 679,981 singleton births in Sweden in 1973-1979, followed up for all-cause and cause-specific mortality through 2008 (ages 29-36 years).

RESULTS

There were 10,656 deaths in 21.5 million person-years of follow-up. Among those still alive at the beginning of each age range, early-term birth relative to those born at 39-42 weeks was associated with increased mortality in the neonatal period (0-27 days: adjusted hazard ratio = 2.18 [95% confidence interval = 1.89-2.51]), postneonatal period (28-364 days: 1.66 [1.44-1.92]), early childhood (1-5 years: 1.29 [1.10-1.51]), and young adulthood (18-36 years: 1.14 [1.05-1.24]), but not in late childhood/adolescence (6-17 years: 0.97 [0.84-1.12]). In young adulthood, early-term birth was strongly associated with death from congenital anomalies and endocrine disorders, especially diabetes (2.89 [1.54-5.43]).

CONCLUSIONS

In this large national cohort study, early-term birth was independently associated with increased mortality in infancy, early childhood, and young adulthood. Lowest short-term and long-term mortality was among those born at 39-42 weeks.

Ethical issues raised by personalized nutrition based on genetic information

Four principles are taken as basis for the ethical analysis: autonomy, nonmaleficence, beneficence, and justice. Health is understood as a limited aspect of wellbeing. Food is understood as an important aspect of wellbeing, not only an instrument for health. Modern society is characterized by a tendency to identify wellbeing with external rather than subjective circumstances, to identify wellbeing with health, and to create exaggerated health expectations. Based upon this understanding, aspects of personalized nutrition are discussed: genetic testing, counselling, and development of special dietary products. Today the predictive value of genetic tests for personal nutrition is limited, and experimental at best. Recommendations for the future: Personalized nutrition must be based on solid knowledge. Phenotypic analyses should be used when adequate. When a genetic test can have a clear advantage, this should be preferred. Opportunistic screening should only be used when clearly beneficial. Specially trained persons should collect information from genetic tests and carry through councelling on a personal basis. Marketing of genetic tests directly sold to the public should be discouraged. Development of special products for personalized nutrition may be necessary in some cases. However, this may also lead to a medicalization of diet.

Association between health-service use and multiplex genetic testing

PURPOSE

The objective of this work was to examine whether offers of multiplex genetic testing increase health-care utilization among healthy patients aged 25-40 years. The identification of genetic variants associated with common disease is accelerating rapidly. "Multiplex tests" that give individuals feedback on large panels of genetic variants have proliferated. Availability of these test results may prompt consumers to use more health-care services.

METHODS

A total of 1,599 continuously insured adults aged 25-40 years were surveyed and offered a multiplex genetic susceptibility test for eight common health conditions. Health-care utilization from automated records was compared in 12-month pre- and posttest periods among persons who completed a baseline survey only (68.7%), those who visited a study website but opted not to test (17.8%), and those who chose the multiplex genetic susceptibility test (13.6%).

RESULTS

In the pretest period, persons choosing genetic testing used an average of 1.02 physician visits per quarter as compared with 0.93 and 0.82 for the baseline-only and Web-only groups, respectively (P < 0.05). There were no statistically significant differences by group in the pretest use of any common medical tests or procedures associated with four common health conditions. When changes in physician and medical test/procedure use in the posttest period were compared among the groups, no statistically significant differences were observed for any utilization category.

CONCLUSIONS

Persons offered and completing multiplex genetic susceptibility testing used more physician visits before testing, but testing was not associated with subsequent changes in use. This study supports the supposition that multiplex genetic testing offers can be provided directly to the patients in such a way that use of health services is not inappropriately increased.

Long-term health outcomes in children born to mothers with diabetes: a population-based cohort study

BACKGROUND

To examine whether prenatal exposure to parental type 1 diabetes, type 2 diabetes, or gestational diabetes is associated with an increased risk of malignant neoplasm or diseases of the circulatory system in the offspring.

METHODS/PRINCIPAL FINDINGS

We conducted a population-based cohort study of 1,781,576 singletons born in Denmark from 1977 to 2008. Children were followed for up to 30 years from the day of birth until the onset of the outcomes under study, death, emigration, or December 31, 2009, whichever came first. We used Cox proportional hazards model to estimate hazard ratios (HR) with 95% confidence intervals (95% CI) for the outcomes under study while adjusting for potential confounders. An increased risk of malignant neoplasm was found in children prenatally exposed to maternal type 2 diabetes (HR = 2.2, 95%CI: 1.5-3.2). An increased risk of diseases of the circulatory system was found in children exposed to maternal type 1 diabetes (HR = 2.2, 95%CI: 1.6-3.0), type 2 diabetes (HR = 1.4, 95%CI: 1.1-1.7), and gestational diabetes (HR = 1.3, 95%CI: 1.1-1.6), but results were attenuated after excluding children with congenital malformations. An increased risk of diseases of the circulatory system was also found in children exposed to paternal type 2 diabetes (HR = 1.5, 95%CI: 1.1-2.2) and the elevated risk remained after excluding children with congenital malformations.

CONCLUSIONS

This study suggests that susceptibility to malignant neoplasm is modified partly by fetal programming. Diseases of the circulatory system may be modified by genetic factors, other time-stable family factors, or fetal programming.

Genetics of Type 2 Diabetes

BACKGROUND

Type 2 diabetes (T2D) is a complex disorder that is affected by multiple genetic and environmental factors. Extensive efforts have been made to identify the disease-affecting genes to better understand the disease pathogenesis, find new targets for clinical therapy, and allow prediction of disease.

CONTENT

Our knowledge about the genes involved in disease pathogenesis has increased substantially in recent years, thanks to genomewide association studies and international collaborations joining efforts to collect the huge numbers of individuals needed to study complex diseases on a population level. We have summarized what we have learned so far about the genes that affect T2D risk and their functions. Although more than 40 loci associated with T2D or glycemic traits have been reported and reproduced, only a minor part of the genetic component of the disease has been explained, and the causative variants and affected genes are unknown for many of the loci.

SUMMARY

Great advances have recently occurred in our understanding of the genetics of T2D, but much remains to be learned about the disease etiology. The genetics of T2D has so far been driven by technology, and we now hope that next-generation sequencing will provide important information on rare variants with stronger effects. Even when variants are known, however, great effort will be required to discover how they affect disease risk.

Meta-analysis of haplotype-association studies: comparison of methods and empirical evaluation of the literature

Background

Meta-analysis is a popular methodology in several fields of medical research, including genetic association studies. However, the methods used for meta-analysis of association studies that report haplotypes have not been studied in detail. In this work, methods for performing meta-analysis of haplotype association studies are summarized, compared and presented in a unified framework along with an empirical evaluation of the literature.

Results

We present multivariate methods that use summary-based data as well as methods that use binary and count data in a generalized linear mixed model framework (logistic regression, multinomial regression and Poisson regression). The methods presented here avoid the inflation of the type I error rate that could be the result of the traditional approach of comparing a haplotype against the remaining ones, whereas, they can be fitted using standard software. Moreover, formal global tests are presented for assessing the statistical significance of the overall association. Although the methods presented here assume that the haplotypes are directly observed, they can be easily extended to allow for such an uncertainty by weighting the haplotypes by their probability.

Conclusions

An empirical evaluation of the published literature and a comparison against the meta-analyses that use single nucleotide polymorphisms, suggests that the studies reporting meta-analysis of haplotypes contain approximately half of the included studies and produce significant results twice more often. We show that this excess of statistically significant results, stems from the sub-optimal method of analysis used and, in approximately half of the cases, the statistical significance is refuted if the data are properly re-analyzed. Illustrative examples of code are given in Stata and it is anticipated that the methods developed in this work will be widely applied in the meta-analysis of haplotype association studies.

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.

Association of CAPN10 gene with insulin sensitivity, glucose tolerance and renal function in essential hypertensive patients

BACKGROUND

Essential hypertension (EH) is a common disorder, which can increase the risk for type 2 diabetes (T2D). Calpain-10 (CAPN10) gene was the first candidate gene of T2D identified through genome-wide linkage and positional cloning, but few works have focused on the relationship of CAPN10 with impaired fasting glucose (IFG) or impaired glucose tolerance (IGT) in EH patients.

METHODS

To identify the effect of UCSNP-43 and UCSNP-44 in CAPN10 gene on susceptibility to IFG/IGT, we conducted a case-control study in 961 EH patients with and without IFG/IGT among Han Chinese population. We also evaluated the impact of two SNPs on insulin sensitivity and glucose tolerance estimated through oral glucose tolerance test and renal functions by blood chemical assays.

RESULTS

The major findings of this study were that UCSNP-43 displayed higher G120 and AUCg. In addition, UCSNP-44 was found associated with IFG/IGT in EH patients, and associated with increased G30, G60, AUCg, Cederholm index, Scr and eGFR. The haplotype UCSNP-43-44 was detected associated with IFG/IGT susceptibility, G60, G120, I0, AUCg, Scr and eGFR by the linear regression with the adjustment for sex, age, BMI, mean blood pressures and ACEI/ARB treatment.

CONCLUSIONS

These findings provided some evidence that CAPN10 gene may play an important role in the pathogenesis of IFG/IGT in EH patients.

Association of calpain-10 gene polymorphism and posttransplant diabetes mellitus in kidney transplant patients medicated with tacrolimus

New-onset, posttransplant diabetes mellitus (PTDM) has a high incidence after kidney transplantation in patients medicated with tacrolimus, and may adversely affect the patient and graft survival. The pathophysiology of PTDM closely mimics that of type II diabetes mellitus (T2DM). One of possible genetic factors predisposing to PTDM might be polymorphism in calpain-10 gene (CAPN10), previously associated with increased risk of T2DM in general population. Therefore, the present study was aimed at evaluation of CAPN10 gene polymorphisms in PTDM in kidney transplant patients medicated with tacrolimus. A total of 214 nondiabetic kidney transplant patients medicated with tacrolimus (56 patients with PTDM and 158 patients without PTDM were genotyped for the presence of CAPN10 gene variants (SNP-43: rs3792267:G>A, SNP-19: rs3842570 ins/del and SNP-63: rs5030952:C>T) using PCR-based assays. Frequency of SNP-63 minor allele was slightly increased in PTDM patients (P=0.056), and an association of SNP-63 heterozygosity and the risk of PTDM (odds ratios (OR)=2.45, P=0.023) was observed. An increased odds for PTDM development in patients carrying 1-1-2 haplotype (rs3792267:G-rs3842570:ins-rs5030952:T) compared to noncarriers was also noted (OR=2.35, P=0.026). Patients' higher body mass index and SNP-63 minor T allele carrier status were identified as independent PTDM risk factors, confirmed by multivariate regression analysis. This is the first study of CAPN10 polymorphism in relation to PTDM risk. However, the application of SNP-63 (rs5030952:C>T) as a marker of PTDM should be verified by further independent studies.

Utility of genetic and non-genetic risk factors in prediction of type 2 diabetes: Whitehall II prospective cohort study

OBJECTIVES

To assess the performance of a panel of common single nucleotide polymorphisms (genotypes) associated with type 2 diabetes in distinguishing incident cases of future type 2 diabetes (discrimination), and to examine the effect of adding genetic information to previously validated non-genetic (phenotype based) models developed to estimate the absolute risk of type 2 diabetes.

DESIGN

Workplace based prospective cohort study with three 5 yearly medical screenings.

PARTICIPANTS

5535 initially healthy people (mean age 49 years; 33% women), of whom 302 developed new onset type 2 diabetes over 10 years.

OUTCOME MEASURES

Non-genetic variables included in two established risk models-the Cambridge type 2 diabetes risk score (age, sex, drug treatment, family history of type 2 diabetes, body mass index, smoking status) and the Framingham offspring study type 2 diabetes risk score (age, sex, parental history of type 2 diabetes, body mass index, high density lipoprotein cholesterol, triglycerides, fasting glucose)-and 20 single nucleotide polymorphisms associated with susceptibility to type 2 diabetes. Cases of incident type 2 diabetes were defined on the basis of a standard oral glucose tolerance test, self report of a doctor's diagnosis, or the use of anti-diabetic drugs.

RESULTS

A genetic score based on the number of risk alleles carried (range 0-40; area under receiver operating characteristics curve 0.54, 95% confidence interval 0.50 to 0.58) and a genetic risk function in which carriage of risk alleles was weighted according to the summary odds ratios of their effect from meta-analyses of genetic studies (area under receiver operating characteristics curve 0.55, 0.51 to 0.59) did not effectively discriminate cases of diabetes. The Cambridge risk score (area under curve 0.72, 0.69 to 0.76) and the Framingham offspring risk score (area under curve 0.78, 0.75 to 0.82) led to better discrimination of cases than did genotype based tests. Adding genetic information to phenotype based risk models did not improve discrimination and provided only a small improvement in model calibration and a modest net reclassification improvement of about 5% when added to the Cambridge risk score but not when added to the Framingham offspring risk score.

CONCLUSION

The phenotype based risk models provided greater discrimination for type 2 diabetes than did models based on 20 common independently inherited diabetes risk alleles. The addition of genotypes to phenotype based risk models produced only minimal improvement in accuracy of risk estimation assessed by recalibration and, at best, a minor net reclassification improvement. The major translational application of the currently known common, small effect genetic variants influencing susceptibility to type 2 diabetes is likely to come from the insight they provide on causes of disease and potential therapeutic targets.

Impaired insulin secretion in transgenic mice over-expressing calpastatin in pancreatic β-cells

Calpains are a family of calcium-activated proteases involved in a number of cellular functions including cell death, proliferation and exocytosis. The finding that variation in the calpain-10 gene increases type 2 diabetes risk in some populations has increased interest in determining the potential role of calpains in pancreatic β-cell function. In the present study, transgenic mice (Cast (RIP)) expressing an endogenous calpain inhibitor, calpastatin, in pancreatic β-cells were used to dissect the role of the calpain system in the regulation insulin secretion in vivo and in vitro. Glucose concentrations after the administration of intraperitoneal glucose were significantly increased in Cast (RIP) mice compared with wildtype littermate controls. This was associated with a reduction in glucose-stimulated insulin secretion in vivo. Using pancreas perfusion, static islet incubation and islet perifusion, it was demonstrated that Cast (RIP) islets hypersecreted insulin at low glucose, but exhibited significantly impaired insulin responses to high glucose. Examination of insulin release and calcium signals from isolated islets indicated that distal components of the insulin exocytotic pathway were abnormal in Cast (RIP) mice. Cast (RIP) islets had modestly reduced expression of Rab3a and other critical components in the late steps of insulin exocytosis. These studies provide the first evidence that blocking endogenous calpain activity partially impairs insulin release in vivo and in vitro by targeting distal components of the insulin exocytotic machinery.

Clinical review: the genetics of type 2 diabetes: a realistic appraisal in 2008

CONTEXT

Over the last few months, genome-wide association studies have contributed significantly to our understanding of the genetic architecture of type 2 diabetes. If and how this information will impact clinical practice is not yet clear.

EVIDENCE ACQUISITION

Primary papers reporting genome-wide association studies in type 2 diabetes or establishing a reproducible association for specific candidate genes were compiled. Further information was obtained from background articles, authoritative reviews, and relevant meeting conferences and abstracts.

EVIDENCE SYNTHESIS

As many as 17 genetic loci have been convincingly associated with type 2 diabetes; 14 of these were not previously known, and most of them were unsuspected. The associated polymorphisms are common in populations of European descent but have modest effects on risk. These loci highlight new areas for biological exploration and allow the initiation of experiments designed to develop prediction models and test possible pharmacogenetic and other applications.

CONCLUSIONS

Although substantial progress in our knowledge of the genetic basis of type 2 diabetes is taking place, these new discoveries represent but a small proportion of the genetic variation underlying the susceptibility to this disorder. Major work is still required to identify the causal variants, test their role in disease prediction and ascertain their therapeutic implications.

The CAPN10 gene is associated with insulin resistance phenotypes in the Spanish population

Cardiovascular disease is the leading cause of morbidity and mortality in the industrialized world. Familial aggregation of cardiovascular risk factors is a frequent finding, but genetic factors affecting its presentation are still poorly understood. The calpain 10 gene (CAPN10) has been associated with type 2 diabetes (T2DM), a complex metabolic disorder with increased risk of cardiovascular disease. Moreover, the CAPN10 gene has been associated with the presence of metabolic syndrome (MS) in T2DM and in polycystic ovary syndrome (PCOS). In this work, we have analysed whether the polymorphisms UCSNP44, -43, -19 and -63 are related to several cardiovascular risk factors in the context of MS. Molecular analysis of CAPN10 gene was performed in 899 individuals randomly chosen from a cross-sectional population-based epidemiological survey. We have found that CAPN10 gene in our population is mainly associated with two indicators of the presence of insulin resistance: glucose levels two hours after a 75-g oral glucose tolerance test (OGTT) and HOMA values, although cholesterol levels and blood pressure values are also influenced by CAPN10 variants. In addition, the 1221/1121 haplogenotype is under-represented in individuals that fulfil the International Diabetes Federation (IDF) diagnostic criteria for MS. Our results suggest that CAPN10 gene is associated with insulin resistance phenotypes in the Spanish population.

Association of calpain-10 polymorphisms with type 2 diabetes in the Tunisian population

BACKGROUND

Genome-wide analyses of the genetic predisposition to type 2 diabetes mellitus (T2DM) in different isolates and populations have identified regions of interest called non insulin-dependent diabetes mellitus (NIDDM) 1, 2, 3 and 4. At the NIDDM1 locus (2q37.3), calpain-10 (CAPN10) encodes for a ubiquitously expressed protease implicated in the two fundamental pathophysiological aspects of T2DM. This is a report of the results of a study of the association of four CAPN10 polymorphisms with T2DM in the Tunisian population.

PARTICIPANTS AND METHODS

A total of 222 T2DM patients with a diabetes duration of 10 years or more and 206 healthy controls were enrolled to analyze the frequency distribution of four CAPN10 polymorphisms (UCSNP-43, UCSNP-19, UCSNP-110 and UCSNP-63) using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in the Tunisian population. We also investigated the association of T2DM with different haplotypes and haplotype combinations.

RESULTS

Only the A allele of UCSNP-43 showed an association with T2DM (odds ratio, OR=1.86). We also identified a novel combination of haplotypes (121/221) defined by three polymorphisms (UCNSP-43, -19 and -63) that is associated with an increased risk of T2DM (OR=2.38).

CONCLUSION

In this study involving the Tunisian population, we identified genetic variants within CAPN10 that are linked with T2DM and a novel haplotype combination, 121/221, associated with an increased susceptibility to T2DM.

The ENPP1 K121Q polymorphism is associated with type 2 diabetes in European populations: evidence from an updated meta-analysis in 42,042 subjects

OBJECTIVE

Functional studies suggest that the nonsynonymous K121Q polymorphism in the ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1) may confer susceptibility to insulin resistance; genetic evidence on its effect on type 2 diabetes, however, has been conflicting. We therefore conducted a new meta-analysis that includes novel unpublished data from the ENPP1 Consortium and recent negative findings from large association studies to address the contribution of K121Q to type 2 diabetes.

RESEARCH DESIGN AND METHODS

After a systematic review of the literature, we evaluated the effect of ENPP1 K121Q on diabetes risk under three genetic models using a random-effects approach. Our primary analysis consisted of 30 studies comprising 15,801 case and 26,241 control subjects. Due to considerable heterogeneity and large differences in allele frequencies across populations, we limited our meta-analysis to those of self-reported European descent and, when available, included BMI as a covariate.

RESULTS

We found a modest increase in risk of type 2 diabetes for QQ homozygotes in white populations (combined odds ratio [OR] 1.38 [95% CI 1.10-1.74], P = 0.005). There was no evidence of publication bias, but we noted significant residual heterogeneity among studies (P = 0.02). On meta-regression, 16% of the effect was accounted for by the mean BMI of control subjects. This association was stronger in studies in which control subjects were leaner but disappeared after adjustment for mean control BMI (combined OR 0.93 [95% CI 0.75-1.15], P = 0.50).

CONCLUSIONS

The ENPP1 Q121 variant increases risk of type 2 diabetes under a recessive model of inheritance in whites, an effect that appears to be modulated by BMI.

Pathogenesis, risk assessment and prevention of type 2 diabetes mellitus

Type 2 diabetes mellitus is a complex, polygenic disease with a heterogeneous pathophysiology, mainly characterised by obesity-associated insulin resistance and a progressive failure of pancreatic beta-cells. Predominant risk factors for its development are abdominal obesity and age; other factors that augment the individual disease risk independent of obesity are the nutritional pattern (low consumption of fibres, high consumption of red meat, saturated and trans fat), lifestyle (smoking, low physical activity), and biomarkers such as blood pressure, HbA1c, serum adiponectin and inflammatory cytokines. These variables can provide the basis for a precise risk assessment and a personalised prevention. Genotyping for the presently known gene variants conferring an increased disease risk adds relatively little to the information provided by the phenotypic risk factors and biomarkers. However, genetic information is necessary for a personalised risk assessment and intervention that begins before phenotypic risk factors are detectable. The incidence of type 2 diabetes can significantly be lowered by reduction of the intraabdominal fat mass (by nutritional intervention and exercise), and by pharmacological control of post-prandial blood glucose excursions. Because of the high portion of non-responders to a preventive intervention, current efforts aim at the identification of phenotypic and genetic variables predicting the success of the intervention.

Definition of phenotype

Definition of the phenotype is crucial in designing any genetic study, especially an association study, intended to detect the disease predisposing genes. In this chapter, we review the different types of phenotypes such as discrete or continuous and discuss the issues impacting on the phenotype definition related to study design, specifically, the impact of diagnostic error (misclassification) in case-control studies and measurement error in continuous traits. We show that the power of a study depends heavily on the phenotype measured and that misclassification or measurement error can dramatically reduce the power. We also suggest some possible responses to these challenges.

The new type 2 diabetes gene TCF7L2

PURPOSE OF REVIEW

Common variants in the gene that encodes the transcription factor 7-like 2 (TCF7L2) have been strongly associated with type 2 diabetes. This highly reproducible association may uncover novel mechanisms of glycemic pathophysiology.

RECENT FINDINGS

The initial publication of an association of common variants in TCF7L2 with type 2 diabetes in people of European descent has been followed by an avalanche of replication reports. These papers not only confirm the original finding, but also extend it to other populations, fine map the source of the association signal, describe its effect on metabolic parameters in humans, open the door to a more precise molecular characterization, and provide an insight into its possible impact on diabetes therapy.

SUMMARY

The discovery of TCF7L2 as a diabetes gene illustrates that novel true diabetes genes can be found, their association with type 2 diabetes replicated and their effect incorporated into risk prediction models. It is hoped that the detection of other such genes in genome-wide association scans will help elucidate the genetic architecture of this disease.

A new era in finding Type 2 diabetes genes-the unusual suspects

In 1988 the task of identifying Type 2 diabetes genes was described as a nightmare. For the next 17 years this proved to be largely correct. In the meantime the prevalence of Type 2 diabetes rose sharply due to non-genetic factors, compounding the problem of trying to find genes. Despite a huge amount of effort, progress was disappointing and only two genes, PPARG and KCNJ11, were confirmed beyond doubt as Type 2 diabetes risk factors in multiple studies. The reasons for this have been well documented and mainly consist of the use of inappropriate levels of statistical inference given the many hundreds of thousands of potential risk polymorphisms in the genome and their small effect sizes. The good news is that these problems are now surmountable and prospects for finding many more genes are bright. This year saw the identification of a third gene, TCF7L2, that has a greater impact on risk than the first two and provided important lessons for Type 2 diabetes genetic studies. The most important of these lessons was that previously unsuspected genes may be involved. In this review I discuss why this year is the start of a new era in our understanding of Type 2 diabetes genes and how this may lead to improved patient care.

Challenges in studies of the genetic basis of Type 2 diabetes

The prevalence of diabetes is increasing worldwide in epidemic proportions. This increase is mainly due to increased incidence and prevalence of Type 2 diabetes, which accounts for 80-90% of all cases of diabetes. The susceptibility to develop Type 2 diabetes is determined by genetic and environmental factors. Major genes responsible for Type 2 diabetes have not yet been identified. The most replicated susceptibility gene for Type 2 diabetes is TCF7L2, recently published by investigators from Iceland. The second most widely replicated association between a genetic variation and the risk of Type 2 diabetes is that of the Pro12Ala polymorphism in the peroxisome proliferator-activated receptor γ2 gene. Furthermore, the common E23K polymorphism in the KCJN11 gene, encoding the ATP-sensitive potassium-channel subunit Kir6.2, and variants in the calpain-10 gene have been associated with increased susceptibility to Type 2 diabetes in meta-analyses. Several studies have investigated the possibility that rare, highly penetrant mutations in the maturity-onset diabetes of the young genes lead to monogenic diabetes, while common polymorphisms increase the susceptibility to Type 2 diabetes. Indeed, there is increasing evidence that single nucleotide polymorphisms in hepatic nuclear factor-4α are significantly associated with the risk of Type 2 diabetes. In this review, different approaches to identify susceptibility genes for Type 2 diabetes are discussed. In particular, the importance of prospective population-based cohort studies and prospective intervention studies are emphasized. Finally, genome-wide association studies using single nucleotide polymorphisms randomly spaced across the entire genome may be useful in the identification of susceptibility genes for Type 2 diabetes.

Genes, diet and type 2 diabetes mellitus: a review

Diabetes mellitus is widely recognized as one of the leading causes of death and disability. While insulin insensitivity is an early phenomenon partly related to obesity, pancreatic beta-cell function declines gradually over time even before the onset of clinical hyperglycemia. Several mechanisms have been proposed to be responsible for insulin resistance, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction, as well as glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, although only a handful of genes have been identified so far. Diabetic management includes diet, exercise and combinations of antihyperglycemic drug treatment with lipid-lowering, antihypertensive, and antiplatelet therapy. Since many persons with type 2 diabetes are insulin resistant and overweight, nutrition therapy often begins with lifestyle strategies to reduce energy intake and increase energy expenditure through physical activity. These strategies should be implemented as soon as diabetes or impaired glucose homoeostasis (pre-diabetes) is diagnosed.

CAPN10 mRNA splicing and decay is not affected by a SNP associated with susceptibility to type 2 diabetes

The mRNA concentration of CAPN10, a T2D susceptibility gene was measured in white blood cells of T2D and healthy subjects, as well as the transcript half-life in two SNP-43 genotyped human cell lines, to evaluate a possible relationship between this SNP-43 and the transcript half-life. T2D patients with the SNP-43 G-allele had 4.6-fold more CAPN10 transcripts compared to subjects with the A-allele. The mRNA half-life of this transcript in 293T cells (SNP-43 G/G) and Jurkat cells (SNP-43 A/A) was of 8h. We provide evidence that in T2D subjects the G-allele increases the CAPN10 mRNA levels. We propose a defective CAPN10 pre-mRNA processing is responsible for the decreased levels of SNP-43 A-allele transcripts in peripheral white cells of healthy and T2D individuals.

Personalised nutrition: status and perspectives

Personalised, genotype-based nutrition is a concept that links genotyping with specific nutritional advice in order to improve the prevention of nutrition-associated, chronic diseases. This review describes the current scientific basis of the concept and discusses its problems. There is convincing evidence that variant genes may indeed determine the biological response to nutrients. The effects of single-gene variants on risk or risk factor levels of a complex disease are, however, usually small and sometimes inconsistent. Thus, information on the effects of combinations of relevant gene variants appears to be required in order to improve the predictive precision of the genetic information. Furthermore, very few associations between genotype and response have been tested for causality in human intervention studies, and little is known about potential adverse effects of a genotype-derived intervention. These issues need to be addressed before genotyping can become an acceptable method to guide nutritional recommendations.

Calpains and their multiple roles in diabetes mellitus

Type 2 diabetes mellitus (T2DM) can lead to death without treatment and it has been predicted that the condition will affect 215 million people worldwide by 2010. T2DM is a multifactorial disorder whose precise genetic causes and biochemical defects have not been fully elucidated, but at both levels, calpains appear to play a role. Positional cloning studies mapped T2DM susceptibility to CAPN10, the gene encoding the intracellular cysteine protease, calpain 10. Further studies have shown a number of noncoding polymorphisms in CAPN10 to be functionally associated with T2DM while the identification of coding polymorphisms, suggested that mutant calpain 10 proteins may also contribute to the disease. Here we review recent studies, which in addition to the latter enzyme, have linked calpain 5, calpain 3, and its splice variants, calpain 2 and calpain 1 to T2DM-related metabolic pathways along with T2DM-associated phenotypes, such as obesity and impaired insulin secretion, and T2DM-related complications, such as epithelial dysfunction and diabetic cataract.