Variants in the Ca V 2.3 (alpha 1E) subunit of voltage-activated Ca2+ channels are associated with insulin resistance and type 2 diabetes in Pima Indians

Association Study of CACNA1D, KCNJ11, KCNQ1, and CACNA1E Single-Nucleotide Polymorphisms with Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a complex chronic disease characterized by decreased insulin secretion and the development of insulin resistance. Previous genome-wide association studies demonstrated that single-nucleotide polymorphisms (SNPs) present in genes coding for ion channels involved in insulin secretion increase the risk of developing this disease. We determined the association of 16 SNPs found in CACNA1D, KCNQ1, KCNJ11, and CACNA1E genes and the increased probability of developing T2DM. In this work, we performed a case-control study in 301 Mexican adults, including 201 cases with diabetes and 100 controls without diabetes. Our findings indicate a moderate association between T2DM and the C allele, and the C/C genotype of rs312480 within CACNA1D. The CAG haplotype surprisingly showed a protective effect, whereas the CAC and CGG haplotypes have a strong association with T2DM. The C allele and C/C genotype of rs5219 were significantly associated with diabetes. Also, an association was observed between diabetes and the A allele and the A/A genotype of rs3753737 and rs175338 in CACNA1E. The TGG and CGA haplotypes were also found to be significantly associated. The findings of this study indicate that the SNPs examined could serve as a potential diagnostic tool and contribute to the susceptibility of the Mexican population to this disease.

Dietary, Cultural and Pathogens-Related Selective Pressures Shaped Differential Adaptive Evolution Among Native Mexican Populations

Native American genetic ancestry has been remarkably implicated with increased risk of diverse health issues in several Mexican populations, especially in relation to the dramatic changes in environmental, dietary, and cultural settings they have recently undergone. In particular, the effects of these ecological transitions and Westernization of lifestyles have been investigated so far predominantly on Mestizo individuals. Nevertheless, indigenous groups, rather than admixed Mexicans, have plausibly retained the highest proportions of genetic components shaped by natural selection in response to the ancient milieu experienced by Mexican ancestors during their pre-Columbian evolutionary history. These formerly adaptive variants have the potential to represent the genetic determinants of some biological traits that are peculiar to Mexican people, as well as a reservoir of loci with possible biomedical relevance. To test such a hypothesis, we used genome-wide genotype data to infer the unique adaptive evolution of Native Mexican groups selected as reasonable descendants of the main pre-Columbian Mexican civilizations. A combination of haplotype-based and gene-network analyses enabled us to detect genomic signatures ascribable to polygenic adaptive traits plausibly evolved by the main genetic clusters of Mexican indigenous populations to cope with local environmental and/or cultural conditions. Some of these adaptations were found to play a role in modulating the susceptibility/resistance of these groups to certain pathological conditions, thus providing new evidence that diverse selective pressures have contributed to shape the current biological and disease-risk patterns of present-day Native and Mestizo Mexican populations.

Cav2.3 channel function and Zn2+-induced modulation: potential mechanisms and (patho)physiological relevance

Voltage-gated calcium channels (VGCCs) are critical for Ca²⁺ influx into all types of excitable cells, but their exact function is still poorly understood. Recent reconstruction of homology models for all human VGCCs at atomic resolution provides the opportunity for a structure-based discussion of VGCC function and novel insights into the mechanisms underlying Ca²⁺ selective flux through these channels. In the present review, we use these data as a basis to examine the structure, function, and Zn²⁺-induced modulation of Ca_v2.3 VGCCs, which mediate native R-type currents and belong to the most enigmatic members of the family. Their unique sensitivity to Zn²⁺ and the existence of multiple mechanisms of Zn²⁺ action strongly argue for a role of these channels in the modulatory action of endogenous loosely bound Zn²⁺, pools of which have been detected in a number of neuronal, endocrine, and reproductive tissues. Following a description of the different mechanisms by which Zn²⁺ has been shown or is thought to alter the function of these channels, we discuss their potential (patho)physiological relevance, taking into account what is known about the magnitude and function of extracellular Zn²⁺ signals in different tissues. While still far from complete, the picture that emerges is one where Ca_v2.3 channel expression parallels the occurrence of loosely bound Zn²⁺ pools in different tissues and where these channels may serve to translate physiological Zn²⁺ signals into changes of electrical activity and/or intracellular Ca²⁺ levels.

1,25-Dihydroxyvitamin D3 enhances glucose-stimulated insulin secretion in mouse and human islets: a role for transcriptional regulation of voltage-gated calcium channels by the vitamin D receptor

AIM

Vitamin D deficiency in rodents negatively affects glucose-stimulated insulin secretion (GSIS) and human epidemiological studies connect poor vitamin D status with type 2 diabetes. Previous studies performed primarily in rat islets have shown that vitamin D can enhance GSIS. However the molecular pathways linking vitamin D and insulin secretion are currently unknown. Therefore, experiments were undertaken to elucidate the transcriptional role(s) of the vitamin D receptor (VDR) in islet function.

METHODS

Human and mouse islets were cultured with vehicle or 1,25-dihydroxyvitamin-D₃ (1,25D₃) and then subjected to GSIS assays. Insulin expression, insulin content, glucose uptake and glucose-stimulated calcium influx were tested. Microarray analysis was performed. In silico analysis was used to identify VDR response elements (VDRE) within target genes and their activity was tested using reporter assays.

RESULTS

Vdr mRNA is abundant in islets and Vdr expression is glucose-responsive. Preincubation of mouse and human islets with 1,25D₃ enhances GSIS and increases glucose-stimulated calcium influx. Microarray analysis identified the R-type voltage-gated calcium channel (VGCC) gene, Cacna1e, which is highly upregulated by 1,25D₃ in human and mouse islets and contains a conserved VDRE in intron 7. Results from GSIS assays suggest that 1,25D₃ might upregulate a variant of R-type VGCC that is resistant to chemical inhibition.

CONCLUSION

These results suggest that the role of 1,25D₃ in regulating calcium influx acts through the R-Type VGCC during GSIS, thereby modulating the capacity of beta cells to secrete insulin.

Chemical genetic-based phenotypic screen reveals novel regulators of gluconeogenesis in human primary hepatocytes

Insulin resistance is a pathophysiological hallmark of type 2 diabetes and nonalcoholic fatty liver disease. Under the condition of fat accumulation in the liver, suppression of hepatic glucose production by insulin is diminished. In order to gain deeper understanding of dysregulation of glucose production in metabolic diseases, in the present study, we performed an unbiased phenotypic screening in primary human hepatocytes to discover novel mechanisms that regulate gluconeogenesis in the presence of insulin. To optimize phenotypic screening process, we used a chemical genetic screening approach by building a small-molecule library with prior knowledge of activity-based protein profiling. The “positive hits” result from the screen will be small molecules with known protein targets. This makes downstream deconvolution process (i.e., determining the relevant biological targets) less time-consuming. To unbiasedly decipher the molecular targets, we developed a novel statistical method and discovered a set of genes, including DDR3 and CACNA1E that suppressed gluconeogenesis in human hepatocytes. Further investigation, including transcriptional profiling and gene network analysis, was performed to understand the molecular functions of DRD3 and CACNA1E in human hepatocytes.

A high-throughput screening protocol helped identify two novel genes involved in sugar metabolism that could be druggable targets for treating type 2 diabetes. Haiqing Hua and colleagues from the Lilly China Research and Development Center, a division of Eli Lilly & Company in Shanghai, evaluated the ability of human liver cells to produce glucose when exposed to a library of more than 1500 small-molecule drugs with known molecular targets. The researchers distinguished a set of genes that, when inhibited, dramatically suppressed glucose production. Two of these genes had not previously been implicated in liver function. The researchers began to dissect that molecular function through studies of gene expression and gene network analysis. The results demonstrate a way to combine chemical genetics and phenotypic screening to identify novel drug targets, revealing two for diabetes.

The interaction between DNA methylation and long non-coding RNA during the onset of puberty in goats

Epigenetics plays an important role in controlling female puberty. Both DNA methylation and long non-coding RNAs (lncRNA) regulate the initiation of puberty by affecting the expression of genes related to puberty. While recent studies have indicated that DNA methylation of lncRNA represses the expression of lncRNA, its role in regulating puberty remains unclear. To explore the mechanism between DNA methylation and lncRNAs during puberty onset, we performed whole-genome bisulphite sequencing (WGBS) and RNA-sequencing (RNA-seq). We found that DNA methylation was inversely correlated to gene expression levels during puberty. Methylation levels gradually decreased near the transcription initiation site and were present at high levels in the exon, intron and 3' untranslated regions. In the promoter, lncRNA expression was negatively related to DNA methylation. We reported hypermethylation in the gene body and downstream of the lncRNA compared with upstream regions. In GO and KEGG analyses, we found enriched target genes of lncRNA, XLOC_960044 and XLOC_767346. During puberty, methylation of these genes increased while expression decreased. Our study indicates that DNA methylation of the promoter is negatively correlated with lncRNA during puberty onset, and methylation regulates the initiation of puberty via lncRNA, which provides new insight into the epigenetic mechanism of puberty onset.

DNA polymorphisms predict time to progression from uncomplicated to complicated Crohn's disease

OBJECTIVE

Most patients with Crohn's disease (CD) are diagnosed with the uncomplicated inflammatory form of the disease (Montreal stage B1). However, the majority of them will progress to complicated stricturing (B2) and penetrating (B3) CD during their lifetimes. The aim of our study was to identify the genetic factors associated with time to progression from uncomplicated to complicated CD.

PATIENTS AND METHODS

Patients with an inflammatory phenotype at diagnosis were followed up for 10 years. Genotyping was carried out using Illumina ImmunoChip. After quality control, association analyses, Bonferroni's adjustments, linear and Cox's regression, and Kaplan-Meier analysis were carried out for 111 patients and Manhattan plots were constructed.

RESULTS

Ten years after diagnosis, 39.1% of the patients still had the inflammatory form and 60.9% progressed to complicated disease, with an average time to progression of 5.91 years. Ileal and ileocolonic locations were associated with the complicated CD (P=1.08E-03). We found that patients with the AA genotype at single-nucleotide polymorphism rs16857259 near the gene CACNA1E progressed to the complicated form later (8.80 years) compared with patients with the AC (5.11 years) or CC (2.00 years) genotypes (P=3.82E-07). In addition, nine single-nucleotide polymorphisms (near the genes RASGRP1, SULF2, XPO1, ZBTB44, HLA DOA/BRD2, HLA DRB1/HLA DQA1, PPARA, PUDP, and KIAA1614) showed a suggestive association with disease progression (P<10). Multivariate Cox's regression analysis on the basis of clinical and genetic data confirmed the association of the selected model with disease progression (P=5.73E-16).

CONCLUSION

Our study confirmed the association between the locus on chromosome 1 near the gene CACNA1E with time to progression from inflammatory to stricturing or penetrating CD. Predicting the time to progression is useful to the clinician in terms of individualizing patients' management.

Contribution of protein kinase Cα in the stimulation of insulin by the down-regulation of Cavβ subunits

Voltage-gated calcium (Cav) channels and protein kinase C (PKC) isozymes are involved in insulin secretion. In addition, Cavβ, one of the auxiliary subunits of Cav channels, also regulates the secretion of insulin as knockout of Cavβ3 (β3(-/-)) subunits in mice led to efficient glucose homeostasis and increased insulin levels. We examined whether other types of Cavβ subunits also have similar properties. In this regard, we used small interfering RNA (siRNA) of these subunits (20 μg each) to down-regulate them and examined blood glucose, serum insulin and PKC translocation in isolated pancreatic β cells of mice. While the down-regulation of Cavβ2 and β3 subunits increased serum insulin levels and caused efficient glucose homeostasis, the down-regulation of Cavβ1 and β4 subunits failed to affect both these parameters. Examination of PKC isozymes in the pancreatic β-cells of Cavβ2- or β3 siRNA-injected mice showed that three PKC isozymes, viz., PKC α, βII and θ, translocated to the membrane. This suggests that when present, Cavβ2 and β3 subunits inhibited PKC activation. Among these three isozymes, only PKCα siRNA inhibited insulin and increased glucose concentrations. It is possible that the activation of PKCs βII and θ is not sufficient for the release of insulin and PKCα is the mediator of insulin secretion under the control of Cavβ subunits. Since Cavβ subunits are present intracellularly, it is possible that they (1) inhibited the translocation of PKC isozymes to the membrane and (2) decreased the interaction between Cav channels and PKC isozymes and thus the secretion of insulin.

Type 2 diabetes mellitus-related genetic polymorphisms in microRNAs and microRNA target sites

MicroRNAs (miRNAs) are important endogenous regulators in eukaryotic gene expression and a broad range of biological processes. MiRNA-related genetic variations have been proved to be associated with human diseases, such as type 2 diabetes mellitus (T2DM). Polymorphisms in miRNA genes (primary miRNAs, precursor miRNAs, mature miRNAs, and miRNA regulatory regions) may be involved in the development of T2DM by changing the expression and structure of miRNAs and target gene expression. Genetic polymorphisms of the 3'-untranslated region (UTR) in miRNA target genes may destroy putative miRNA binding sites or create new miRNA binding sites, which affects the binding of UTRs with miRNAs, finally resulting in susceptibility to and development of T2DM. Therefore, focusing on studies into genetic polymorphisms in miRNAs or miRNA binding sites will help our understanding of the pathophysiology of T2DM development and lead to better health management. Herein, we review the association of genetic polymorphisms in miRNA and miRNA targets genes with T2DM development.

Associations of circulating calcium and 25-hydroxyvitamin D with glucose metabolism in pregnancy: a cross-sectional study in European and South Asian women

BACKGROUND

Vitamin D deficiency is thought to impair insulin action and glucose metabolism; however, previous studies have not examined ethnic differences or the influence of calcium and parathyroid hormone. We investigated this in a cohort of predominantly white European and south Asian women during pregnancy.

METHODS

In this cross-sectional study from an urban population in northern England (53.8°N), 1467 women were recruited when undergoing glucose tolerance testing (75 g oral glucose tolerance test) at 26 weeks' gestation.

RESULTS

Gestational diabetes mellitus (GDM) was diagnosed in 137 women (9.3%). Median 25-hydroxyvitamin D concentration for the study population was 9.3 ng/mL (interquartile range 5.2, 16.9) and was higher in European [15.2 ng/mL (10.7, 23.5)] than in south Asian women [5.9 ng/mL (3.9, 9.4), P < .001]. After appropriate adjustment for confounders, 25-hydroxyvitamin D showed a weak inverse association with fasting plasma glucose (FPG; mean difference 1.0% per 1 SD; the ratio of geometric means (RGM) 0.99, 95% confidence interval (CI) 0.98, 1.00), and PTH was weakly associated with FPG (RGM 1.01, 95% CI 1.00, 1.02), but neither was associated with fasting insulin, postchallenge glucose, or GDM. Serum calcium (albumin adjusted) was strongly associated with fasting insulin (RGM 1.06; 95% CI 1.03, 1.08), postchallenge glucose (RGM 1.03, 95% CI 1.01, 1.04), and GDM (odds ratio 1.33, 95% CI 1.06, 1.66) but not with FPG. Associations were similar in European and south Asian women.

CONCLUSIONS

These findings do not indicate any important association between vitamin D status and glucose tolerance in pregnancy. Relationships between circulating calcium and glucose metabolism warrant further investigation.

Association between genetic polymorphisms in Ca(v)2.3 (R-type) Ca2+ channels and fentanyl sensitivity in patients undergoing painful cosmetic surgery

Individual differences in the sensitivity to fentanyl, a widely used opioid analgesic, lead to different proper doses of fentanyl, which can hamper effective pain treatment. Voltage-activated Ca(2+) channels (VACCs) play a crucial role in the nervous system by controlling membrane excitability and calcium signaling. Ca(v)2.3 (R-type) VACCs have been especially thought to play critical roles in pain pathways and the analgesic effects of opioids. However, unknown is whether single-nucleotide polymorphisms (SNPs) of the human CACNA1E (calcium channel, voltage-dependent, R type, alpha 1E subunit) gene that encodes Cav2.3 VACCs influence the analgesic effects of opioids. Thus, the present study examined associations between fentanyl sensitivity and SNPs in the human CACNA1E gene in 355 Japanese patients who underwent painful orofacial cosmetic surgery, including bone dissection. We first conducted linkage disequilibrium (LD) analyses of 223 SNPs in a region that contains the CACNA1E gene using genomic samples from 100 patients, and a total of 13 LD blocks with 42 Tag SNPs were observed within and around the CACNA1E gene region. In the preliminary study using the same 100 genomic samples, only the rs3845446 A/G SNP was significantly associated with perioperative fentanyl use among these 42 Tag SNPs. In a confirmatory study using the other 255 genomic samples, this SNP was also significantly associated with perioperative fentanyl use. Thus, we further analyzed associations between genotypes of this SNP and all of the clinical data using a total of 355 samples. The rs3845446 A/G SNP was associated with intraoperative fentanyl use, 24 h postoperative fentanyl requirements, and perioperative fentanyl use. Subjects who carried the minor G allele required significantly less fentanyl for pain control compared with subjects who did not carry this allele. Although further validation is needed, the present findings show the possibility of the involvement of CACNA1E gene polymorphisms in fentanyl sensitivity.

How "Pharmacoresistant" is Cav2.3, the Major Component of Voltage-Gated R-type Ca2+ Channels?

Membrane-bound voltage-gated Ca²⁺ channels (VGCCs) are targets for specific signaling complexes, which regulate important processes like gene expression, neurotransmitter release and neuronal excitability. It is becoming increasingly evident that the so called “resistant” (R-type) VGCC Ca_v2.3 is critical in several physiologic and pathophysiologic processes in the central nervous system, vascular system and in endocrine systems. However its eponymous attribute of pharmacologic inertness initially made in depth investigation of the channel difficult. Although the identification of SNX-482 as a fairly specific inhibitor of Ca_v2.3 in the nanomolar range has enabled insights into the channels properties, availability of other pharmacologic modulators of Ca_v2.3 with different chemical, physical and biological properties are of great importance for future investigations. Therefore the literature was screened systematically for molecules that modulate Ca_v2.3 VGCCs.

CACNA1E variants affect beta cell function in patients with newly diagnosed type 2 diabetes. the Verona newly diagnosed type 2 diabetes study (VNDS) 3

Background

Genetic variability of the major subunit (CACNA1E) of the voltage-dependent Ca²⁺ channel Ca_V2.3 is associated to risk of type 2 diabetes, insulin resistance and impaired insulin secretion in nondiabetic subjects. The aim of the study was to test whether CACNA1E common variability affects beta cell function and/or insulin sensitivity in patients with newly diagnosed type 2 diabetes.

Methodology/Principal Findings

In 595 GAD-negative, drug naïve patients (mean±SD; age: 58.5±10.2 yrs; BMI: 29.9±5 kg/m², HbA1c: 7.0±1.3) with newly diagnosed type 2 diabetes we: 1. genotyped 10 tag SNPs in CACNA1E region reportedly covering ∼93% of CACNA1E common variability: rs558994, rs679931, rs2184945, rs10797728, rs3905011, rs12071300, rs175338, rs3753737, rs2253388 and rs4652679; 2. assessed clinical phenotypes, insulin sensitivity by the euglycemic insulin clamp and beta cell function by state-of-art modelling of glucose/C-peptide curves during OGTT. Five CACNA1E tag SNPs (rs10797728, rs175338, rs2184945, rs3905011 and rs4652679) were associated with specific aspects of beta cell function (p<0.05−0.01). Both major alleles of rs2184945 and rs3905011 were each (p<0.01 and p<0.005, respectively) associated to reduced proportional control with a demonstrable additive effect (p<0.005). In contrast, only the major allele of rs2253388 was related weakly to more severe insulin resistance (p<0.05).

Conclusions/Significance

In patients with newly diagnosed type 2 diabetes CACNA1E common variability is strongly associated to beta cell function. Genotyping CACNA1E might be of help to infer the beta cell functional phenotype and to select a personalized treatment.

Chemical methods to induce Beta-cell proliferation

Pancreatic beta-cell regeneration, for example, by inducing proliferation, remains an important goal in developing effective treatments for diabetes. However, beta cells have mainly been considered quiescent. This "static" view has recently been challenged by observations of relevant physiological conditions in which metabolic stress is compensated by an increase in beta-cell mass. Understanding the molecular mechanisms underlining these process could open the possibility of developing novel small molecules to increase beta-cell mass. Several cellular cell-cycle and signaling proteins provide attractive targets for high throughput screening, and recent advances in cell culture have enabled phenotypic screening for small molecule-induced beta-cell proliferation. We present here an overview of the current trends involving small-molecule approaches to induce beta-cell regeneration by proliferation.

Channeling dysglycemia: ion-channel variations perturbing glucose homeostasis

Maintaining blood glucose homeostasis is a complex process that depends on pancreatic islet hormone secretion. Hormone secretion from islets is coupled to calcium entry which results from regenerative islet cell electrical activity. Therefore, the ionic mechanisms that regulate calcium entry into islet cells are crucial for maintaining normal glucose homeostasis. Genome-wide association studies (GWAS) have identified single-nucleotide polymorphisms (SNPs), including five located in or near ion-channel or associated subunit genes, which show an association with human diseases characterized by dysglycemia. This review focuses on polymorphisms and mutations in ion-channel genes that are associated with perturbations in human glucose homeostasis and discusses their potential roles in modulating pancreatic islet hormone secretion.

Calcium signaling in the islets

Easy access to rodent islets and insulinoma cells and the ease of measuring Ca(2+) by fluorescent indicators have resulted in an overflow of data that have clarified minute details of Ca(2+) signaling in the rodent islets. Our understanding of the mechanisms and the roles of Ca(2+) signaling in the human islets, under physiological conditions, has been hugely influenced by uncritical extrapolation of the rodent data obtained under suboptimal experimental conditions. More recently, electrophysiological and Ca(2+) studies have elucidated the ion channel repertoire relevant for Ca(2+) signaling in the human islets and have examined their relative importance. Many new channels belonging to the transient receptor potential (TRP) family are present in the beta-cells. Ryanodine receptors, nicotinic acid adenine dinucleotide phosphate channel, and Ca(2+)-induced Ca(2+) release add new dimension to the complexity of Ca(2+) signaling in the human beta-cells. A lot more needs to be learnt about the roles of these new channels and CICR, not because that will be easy but because that will be difficult. Much de-learning will also be needed. Human beta-cells do not have a resting state in the normal human body even under physiological fasting conditions. Their membrane potential under physiologically relevant resting conditions is approximately -50 mV. Biphasic insulin secretion is an experimental epiphenomenon unrelated to the physiological pulsatile insulin secretion into the portal vein in the human body. Human islets show a wide variety of electrical activities and patterns of [Ca(2+)](i) changes, whose roles in mediating pulsatile secretion of insulin into the portal vein remain questionable. Future studies will hopefully be directed toward a better understanding of Ca(2+) signaling in the human islets in the context of the pathogenesis and treatment of human diabetes.

Identification of small-molecule inducers of pancreatic beta-cell expansion

To identify small molecules that can induce beta-cell replication, a large chemical library was screened for proliferation of growth-arrested, reversibly immortalized mouse beta cells by using an automated high-throughput screening platform. A number of structurally diverse, active compounds were identified, including phorbol esters, which likely act through protein kinase C, and a group of thiophene-pyrimidines that stimulate beta-cell proliferation by activating the Wnt signaling pathway. A group of dihydropyridine (DHP) derivatives was also shown to reversibly induce beta-cell replication in vitro by activating L-type calcium channels (LTCCs). Our data suggest that the LTCC agonist 2a affects the expression of genes involved in cell cycle progression and cellular proliferation. Furthermore, treatment of beta cells with both LTCC agonist 2a and the Glp-1 receptor agonist Exendin-4 showed an additive effect on beta-cell replication. The identification of small molecules that induce beta-cell proliferation suggests that it may be possible to reversibly expand other quiescent cells to overcome deficits associated with degenerative and/or autoimmune diseases.

PCLO variants are nominally associated with early-onset type 2 diabetes and insulin resistance in Pima Indians

OBJECTIVE

A prior genome-wide association (GWA) study in Pima Indians identified variants within PCLO that were associated with early-onset type 2 diabetes. PCLO encodes a presynaptic cytomatrix protein that functions as a Ca(2+) sensor that may be involved in insulin secretion and/or insulin action. Therefore, PCLO was analyzed as a candidate gene for type 2 diabetes.

RESEARCH DESIGN AND METHODS

Sequencing of PCLO identified four nonsynonymous variants and a 10-amino acid insertion. These variants, together with 100 additional variants identified by sequencing or chosen from databases, were genotyped for association analysis in the same 895 subjects analyzed in the prior GWA study (300 case subjects with diabetes onset at aged <25 years, 334 nondiabetic control subjects aged >45 years, and 261 discordant siblings of the case or control subjects for within-family analyses), as well as 415 nondiabetic Pima Indians who had been metabolically phenotyped for predictors of diabetes. Selected variants were further genotyped in a population-based sample of 3,501 Pima Indians.

RESULTS

Four variants were modestly associated with early-onset type 2 diabetes in both general and within-family analyses (P = 0.004-0.04, recessive model), where the diabetes risk allele was also nominally associated with a lower insulin-mediated glucose disposal rate (P = 0.009-0.14, recessive model) in nondiabetic Pima Indians. However, their association with diabetes in the population-based sample was weaker (P = 0.02-0.20, recessive model).

CONCLUSIONS

Variation within PCLO may have a modest effect on early-onset type 2 diabetes, possibly as a result of reduced insulin action, but has minimal, if any, impact on population-based risk for type 2 diabetes.

[Human calcium channelopathies. Voltage-gated Ca(2+) channels in etiology, pathogenesis, and pharmacotherapy of neurologic disorders]

Voltage-gated calcium channels are key components in a variety of physiological processes. Within the last decade an increasing number of voltage-gated Ca(2+) channelopathies in both humans and animal models has been described, most of which are related to the neurologic and muscular system. In humans, mutations were found in L-type Ca(v)1.2 and Ca(v)1.4 Ca(2+) channels as well as the non-L-type Ca(v)2.1 and T-type Ca(v)3.2 channels, resulting in altered electrophysiologic properties. Based on their widespread distribution within the CNS, voltage-gated calcium channels are of particular importance in the etiology and pathogenesis of various forms of epilepsy and neuropsychiatric disorders. In this review we characterise the different human Ca(2+) channelopathies known so far, further illuminating basic pathophysiologic mechanisms and clinical aspects.