Evidence for association between the class I subset of the insulin gene minisatellite (IDDM2 locus) and IDDM in the Japanese population

Association of insulin gene VNTR INS -23/Hph1 A>T (rs689) polymorphism with type 1 diabetes mellitus in Egyptian children

Background

Type1 diabetes mellitus (T1DM) has a multi-factorial pathogenesis; the interplay between genetic susceptibility and environmental factors is thought to provide the fundamental element for the disease. Apart from HLA, more than 50 genetic variants are associated with T1DM. INS -23/Hph1 A>T (rs689) is one of the effective loci with inconsistent reports in the literature. Accordingly, this study was designed to define the frequencies of INS -23/Hph1 A>T polymorphism and its association with T1DM in Egyptian diabetic children and their non-diabetic family members as compared to healthy controls.

Methods

Using polymerase chain reaction-restriction fragment length polymorphism methodology, analysis of insulin gene VNTR polymorphism was performed for 496 samples (91 patients, 179 parents, 130 siblings, and 96 controls); parents and siblings were apparently healthy.

Results

INS genotypes and allele frequencies were comparable between patients, non-diabetic siblings, and parents (p = 0.97 and 0.77, respectively). However, the TT/AT genotype and T allele were over-presented in the three family groups compared to controls (p = 0.0015 and 0.0029, respectively).

Comparing patients to controls, the T allele is considered a risk factor for the development of TIDM (OR 2.56, 95% CI 1.42–4.62, p = 0.0017).

INS -23/Hph1 A>T polymorphism showed concordance between patients and their mothers (Kappa = 0.446, p = 0.000) but not with their fathers (Kappa = 0.031, p = 0.765).

Conclusions

INS -23/Hph1 A>T gene polymorphism was shown to be a risk factor for the development of TIDM. This is in agreement with some and in disagreement with other reports. Studies of risk susceptibility factors have to be carried out locally in each community; results cannot be extrapolated from one ethnic group to another.

G Allele of the IGF2 ApaI Polymorphism Is Associated With Judo Status

Itaka, T, Agemizu, K, Aruga, S, and Machida, S. G allele of the IGF2 ApaI polymorphism is associated with judo status. J Strength Cond Res 30(7): 2043-2048, 2016-Previous studies have reported that the insulin-like growth factor 2 (IGF2) ApaI polymorphism is associated with body mass index, fat mass, and grip strength. Competitive judo requires high levels of strength and power. The purpose of this study was to investigate the association between the IGF2 ApaI and ACTN3 R577X polymorphisms and judo status. The subjects were 156 male judo athletes from a top-level university in Japan. They were divided into 3 groups based on their competitive history: international-level athletes, national-level athletes, and others. Genomic DNA was extracted from the saliva of each athlete, and the maximal isometric strength of the trunk muscles and handgrip strength were measured. Genotyping by polymerase chain reaction-restriction fragment length polymorphism was used to detect IGF2 (rs680) and α-actinin-3 (ACTN3) (rs1815739) gene polymorphisms. The genotype frequencies of the 2 gene polymorphisms were compared among the 3 groups of judo athletes and controls. International-level judo athletes showed a higher frequency of the GG + GA genotype of the IGF2 gene than that of the national-level athletes and others. There was an inverse linear correlation between the frequency of the IGF2 AA genotype and level of judo performance (p = 0.041). Back muscle strength relative to height and weight was higher in subjects with the GG + GA genotype than in those with the AA genotype. Conversely, the ACTN3 R577X polymorphism was not associated with judo status. Additionally, no differences were found in back muscle or handgrip strength among the ACTN3 genotypes. In conclusion, the results indicate that the IGF2 gene polymorphism may be associated with judo status.

Novel avenues of drug discovery and biomarkers for diabetes mellitus

Globally, developed nations spend a significant amount of their resources on health care initiatives that poorly translate into increased population life expectancy. As an example, the United States devotes 16% of its gross domestic product to health care, the highest level in the world, but falls behind other nations that enjoy greater individual life expectancy. These observations point to the need for pioneering avenues of drug discovery to increase life span with controlled costs. In particular, innovative drug development for metabolic disorders such as diabetes mellitus becomes increasingly critical given that the number of diabetic people will increase exponentially over the next 20 years. This article discusses the elucidation and targeting of novel cellular pathways that are intimately tied to oxidative stress in diabetes mellitus for new treatment strategies. Pathways that involve wingless, β-nicotinamide adenine dinucleotide (NAD(+)) precursors, and cytokines govern complex biological pathways that determine both cell survival and longevity during diabetes mellitus and its complications. Furthermore, the role of these entities as biomarkers for disease can further enhance their utility irrespective of their treatment potential. Greater understanding of the intricacies of these unique cellular mechanisms will shape future drug discovery for diabetes mellitus to provide focused clinical care with limited or absent long-term complications.

The association of variable number of tandem repeats of the insulin gene with susceptibility to type 1 diabetes among Korean subjects

BACKGROUND

There is ethnic variation in the variable number of tandem repeats of the insulin gene (INS VNTR), one of the susceptibility loci for developing type 1 diabetes (T1D). We evaluated the influence of the genotypes and subdivisions of INS VNTR on the development of T1D in Korean subjects.

METHODS

The study included 352 Korean patients, under the age of 18 years who were diagnosed as having T1D, and 356 control subjects. The insulin - 23HphI A/T single nucleotide polymorphism was used as a marker of class I and III alleles. Surrounding polymorphisms at nucleotide positions + 1127, + 1140, + 2331 and + 2336 were determined as subdivisions of INS VNTR.

RESULTS

Classes I/I, I/III and III/III were observed at frequencies of 95.8, 4.2 and 0% among all subjects, respectively. Class I/III genotype was significantly less frequent in patients with T1D than in controls (2.56 versus 5.90%; odds ratio 0.419; P = 0.039). In a subdivision analysis, the ID/ID genotype was decreased among patients (P = 0.017, adjusted P = 0.085) and the IC allele tended to increase. The frequency of the class I/III genotype was significantly lower among patients who were diagnosed when younger than 7 years of age than in controls (odds ratio 0.115; P = 0.011).

CONCLUSIONS

INS VNTR has predominance of class I over class III alleles and is associated with susceptibility to T1D in Koreans. In addition, INS VNTR shows distinctive susceptibility according to the age at the onset of T1D.

Stroke pharmacogenomics

Circulatory disease accounts for fifteen million deaths each year, of which stroke accounts for four and a half million- with an estimated nine million stroke survivors annually. The overall incidence rate of stroke is 2 to 2.5 per thousand adults with an approximate prevalence of 5 per thousand and an estimated 5-year risk of stroke recurrence of 15 to 40 percent. Conventional risk factors for stroke include: increasing age, hypertension, diabetes mellitus, smoking, increased body mass index, ischemic heart disease, heart failure, atrial fibrillation and lack of physical activity. Age is the strongest risk factor for both ischemic and haemorrhagic stroke with its incidence doubling for each successive decade after the age of fifty-five years. However, there is a substantial portion of patients with significant cerebrovascular disease who do not have any of these stroke risk-factors, leading to the speculation that there are other factors that have not been identified yet So as to improve diagnosis and treatment strategies, as well as to reduce the related public health burden, it could be helpful to successfully identify its extremely complex genetic determinants (polygenic, multiple genes play a role). Pharmacogenetics is the field of pharmacology that deals with the influence of genetic variation on drug response by correlating gene expression and gene variants with the efficacy or toxicity of drugs. The principle drugs in stroke medicine are antithrombotics. The aim of this paper was to review the most commonly used drugs for stroke such as rtPA in the acute phase as well as antiplatelets and wafarin for secondary prophylaxis.

Trinucleotide repeats of programmed cell death-1 gene are associated with susceptibility to type 1 diabetes mellitus

Multiple genes are involved in conferring susceptibility to autoimmune type 1 diabetes mellitus. The immunoreceptor programmed cell death-1 (PDCD-1), an inhibitory costimulatory molecule regulating peripheral tolerance, is reported to play an important role in the development of type 1 diabetes mellitus, making the human PDCD-1 gene, PDCD1, a candidate for disease susceptibility. The aim of this study was to clarify the contribution of PDCD1 to genetic susceptibility to type 1 diabetes mellitus in humans. To screen for sequence variants, we sequenced all 5 exons and exon-intron junctions of PDCD1 in Japanese subjects, 16 with type 1 diabetes mellitus and 16 without the disease. Some of the sequence variations identified were genotyped in larger samples (n = 275) with and without type 1 diabetes mellitus by polymerase chain reaction restriction fragment length polymorphism method or a fluorescence-based method. The distributions of polymorphisms were compared between patients with type 1 diabetes mellitus and healthy controls by contingency table analysis and Pearson chi(2) test. In this study, we found 16 sequence variants, including a TGC repeating variant in the 3' untranslated region. We found this variant to be associated with the development of type 1 diabetes mellitus. These data suggest the contribution of PDCD1 and its gene product to the development of type 1 diabetes mellitus.

Genetic variations within the insulin gene region are associated with accelerated fetal growth

Size at birth has been proposed to be associated with the risk of type 2 diabetes and cardiovascular disease later in life. It is, however, unclear whether this association is attributed to an unfavorable intrauterine environment or to specific genotypes predisposing both altered fetal growth and common diseases in adult life. The aim of this study was to investigate the associations between the neonatal birth size and the genotypes of polymorphic loci within the insulin gene (INS) region, which is susceptible to diabetes mellitus. We analyzed the genotypes of two polymorphic loci; -23HphI and HUMTH01, in 520 pairs of normal Japanese mothers and their neonates, and compared with the somatoscopic characteristics at birth converted into standard deviation scores (SDS) according to sex, parity and gestational weeks at delivery. It was revealed that neonatal -23HphI T allele and HUMTH01 allele10, which are linked to the INS variable number of tandem repeats (VNTR) class III allele, were associated with increased weight, head circumstance, and length at birth. These associations confirmed that variation within the INS region, most probably at the INS-VNTR, influences fetal growth. Furthermore, the finding that the paternally transmitted -23HphI T allele was exclusively correlated with increased size at birth indicates the involvement of an imprinting mechanism. In conclusion, the INS-VNTR class III allele might accelerate fetal growth in a parent-specific manner.

Oxidative stress biology and cell injury during type 1 and type 2 diabetes mellitus

Diabetes mellitus (DM) affects approximately 170 million individuals worldwide and is expected to alter the lives of at least 366 million individuals within a future span of 25 years. Of even greater concern is the premise that these projections are underestimated since they assume obesity levels will remain constant. Type 1 insulin-dependent DM accounts for only 5-10 percent of all diabetics but represents a highly significant health concern, since this disorder begins early in life and leads to long-term complications. In contrast, Type 2 DM is recognized as the etiology of over 80 percent of all diabetics and is dramatically increasing in incidence as a result of changes in human behavior and increased body mass index. Yet, the pathological consequences of these disorders that involve the both the neuronal and vascular systems are intimately linked through the pathways that mediate oxidative stress. Here we highlight some of the relevant oxidative pathways that determine insulin resistance through reactive oxygen species, mitochondrial dysfunction, uncoupling proteins, and endoplasmic reticulum stress. These pathways are ultimately linked to protein kinase B (Akt) and the insulin signaling pathways that determine the initial onset of glucose intolerance and the subsequent course to apoptotic cell injury. Through the elucidation of these targets, improvement in current strategies as well as the development of future clinical applications can move forward for both the prevention and treatment of Type 1 and Type 2 DM.

Mechanistic insights into diabetes mellitus and oxidative stress

Diabetes mellitus (DM) is a significant healthcare concern worldwide that affects more than 165 million individuals leading to cardiovascular disease, nephropathy, retinopathy, and widespread disease of both the peripheral and central nervous systems. The incidence of undiagnosed diabetes, impaired glucose tolerance, and impaired fasting glucose levels raises future concerns in regards to the financial and patient care resources that will be necessary to care for patients with DM. Interestingly, disease of the nervous system can become one of the most debilitating complications and affect sensitive cognitive regions of the brain, such as the hippocampus that modulates memory function, resulting in significant functional impairment and dementia. Oxidative stress forms the foundation for the induction of multiple cellular pathways that can ultimately lead to both the onset and subsequent complications of DM. In particular, novel pathways that involve metabotropic receptor signaling, protein-tyrosine phosphatases, Wnt proteins, Akt, GSK-3beta, and forkhead transcription factors may be responsible for the onset and progression of complications form DM. Further knowledge acquired in understanding the complexity of DM and its ability to impair cellular systems throughout the body will foster new strategies for the treatment of DM and its complications.

Type 1 diabetes in Japan

Type 1 diabetes is a multifactorial disease which results from a T-cell-mediated autoimmune destruction of the pancreatic beta cells in genetically predisposed individuals. The risk for individuals of developing type 1 diabetes varies remarkably according to country of residence and race. Japan has one of the lowest incidence rates of type 1 diabetes in the world, and recognises at least three subtypes of the condition: acute-onset ('classical'), slow-onset, and fulminant type 1 diabetes. The incidence rate of type 1 diabetes in children aged 0-14 years in Japan increased over the period from 1973-1992, but remained constant over the last decade, averaging 2.37 cases per 100,000 persons per year; the incidence does not appear to have increased in older age groups. Although there are few reports regarding the incidence and prevalence of type 1 diabetes in adult-onset patients, it appears that the prevalence of type 1 diabetes in adults is more than twice that in childhood-onset patients and that two-thirds of them have a slow-onset form of type 1 diabetes. Differences and similarities in the association of MHC and non-MHC genes with type 1 diabetes are observed in Japan and in countries with Caucasoid populations. Highly susceptible class II HLA haplotypes identified in patients of Caucasoid origin are rarely seen in Japanese patients, whereas protective haplotypes are universal. Non-MHC genes associated with susceptibility to type 1 diabetes in both Japanese and Caucasoid patients include polymorphisms in the insulin gene, the cytotoxic T-lymphocyte antigen 4 (CTLA4) gene, the interleukin-18 (IL18) gene and the major histocompatibility complex class I chain-related gene A (MICA) gene. Fulminant type 1 diabetes is a unique subtype of type 1 diabetes that accounts for about 20% of acute-onset type 1 diabetes, and is seen mainly in adults. The challenge for the future is to investigate the underlying pathogenesis of beta cell destruction, including the genetic or environmental factors that may modify the form of onset for each subtype of Japanese type 1 diabetes.

Variable number of tandem repeats of the insulin gene determines susceptibility to latent autoimmune diabetes in adults

BACKGROUND

The different clinical presentations of latent autoimmune diabetes in adults (LADA) and type 1 diabetes mellitus may be the result of susceptibility genes in determining the mode of onset. We analyzed the 5' polymorphisms of the insulin mini-satellite region (INS), a variable number of tandem repeats (VNTR) [repeat units; RU]. We evaluated the association of the different INS-VNTR alleles in patient susceptibility to LADA autoimmune diabetes. To our knowledge, this constitutes the first study of this kind performed in a Caucasian population.

METHODS

From an group of 160 Argentinean patients previously characterized as having LADA, we selected 44 patients who presented with humoral autoimmunity for genotyping and compared them to 88 patients with type 1 diabetes and 138 healthy individuals. The INS-VNTR allele classes were determined by Southern blotting (class I: 21-44RU; class III: 138-159RU). Subjects with class I alleles were further studied using PCR amplification to determine the exact length of the alleles (short 1S: 22-37RU; medium 1M: 38-41RU; large 1L: 42-43RU). Allelic and genotype frequencies were estimated by chi(2) tests for independence with 2 x 2 contingency tables and the relative risks (RR) were determined using GraphPad InStat software.

RESULTS

We observed differential associations among the class I alleles when comparing patients with LADA (80.6%) and type 1 diabetes (81.3%) with the controls (70%; p < 0.005). This increase was largely due to the high frequency of the 1S/S genotype (63.6% LADA vs 37% controls, with a p-value of 0.0019 [p1]; 53.4% type 1 diabetes vs 37% controls, with a p-value of 0.0149 [p2]). Remarkably, all LADA patients genotyped as class I homozygous had the shorter (S) class I allele (100%). Differences in the overall 1S distribution were observed: in LADA the 94.4% of the alleles were equal to or smaller than 35RU, while in patients with type 1 diabetes it was 78.3% and in controls 74.1%. Moreover, the relative risks associated with the 1S/S genotype for patients with LADA showed a substantial increase with respect to those with type 1 diabetes (52%) when we compare them to the controls (1S/S LADA/control, 2.282 [RR1] vs type 1 diabetes/control, 1.497 [RR2]).

CONCLUSION

The presence of the 1S allele could be considered a risk factor in LADA patients, as previously reported for type 1 diabetes. The class I INS-VNTR allele in LADA increases genetic susceptibility to disease development.

IDDM2/insulin VNTR modifies risk conferred by IDDM1/HLA for development of Type 1 diabetes and associated autoimmunity

AIM/HYPOTHESIS

Type 1 diabetes (T1D) is an autoimmune disease with multiple susceptibility genes. The aim of this study was to determine whether combining IDDM1/HLA and IDDM2/ insulin( INS) 5' variable number of tandem repeat locus (VNTR) genotypes improves T1D risk assessment.

METHODS

Patients with T1D (n=488), control subjects (n=846), and offspring of parents with T1D (n=1122) were IDDM1 and IDDM2 genotyped. Offspring were followed for islet autoantibodies and T1D from birth until the age of 2 to 12 years.

RESULTS

Compared to the I/I INS VNTR genotype, the I/III and III/III genotypes reduced T1D risk conferred by IDDM1/HLA in all HLA genotype categories of the case-control cohort by 1.6-fold to three-fold. The highest T1D risk was associated with INS VNTR class I/I plus HLA DR3/DR4-DQ8 (20.4% in patients, 0.6% in control subjects) or HLA DR4-DQ8/DR4-DQ8 (6.3% in patients, 0.2% in control subjects). In the offspring, HLA DR3/DR4-DQ8 and DR4-DQ8/DR4-DQ8 conferred increased risk for early development of islet autoantibodies (14.6% and 12.9% by age 2 years). Offspring with these high risk IDDM1 genotypes plus the INS VNTR class I/I genotype (n=71; 6.3%) had the highest risk of developing islet autoantibodies (21.8% by age 2 years vs 8.9% in offspring with high risk IDDM1 plus INS VNTR class I/III or III/III genotypes, p<0.05) and T1D (8.5% by age 6 years vs 4.3%). Offspring who developed autoantibodies to multiple antigens had increased frequencies of both high risk IDDM1 and IDDM2 genotypes (p<0.0001), whereas offspring who developed autoantibodies to GAD only had increased frequencies of high risk IDDM1 and protective IDDM2 genotypes, suggesting that IDDM2 influences the autoimmune target specificity.

CONCLUSION/INTERPRETATION

Combining IDDM1 and IDDM2 genotyping identifies a minority of children with an increased T1D risk.

Current knowledge of Japanese type 1 diabetic syndrome

The Japanese have one of the lowest incidence of childhood type 1 diabetes in the world, but the incidence of this disease is clearly increasing within the Japanese population, as reported in several European countries. Latent autoimmune diabetes mellitus in adult (LADA) patients are also likely to have a lower incidence compared to Caucasians. Among the non-autoimmune (type 1B) diabetes in Japanese adults, there exists a novel subtype of type 1 diabetes characterized by extremely rapid onset and pancreatic exocrine inflammation. HLA and non-HLA gene associations to type 1 diabetes may vary depending on ethnic origin. Highly susceptible HLA haplotypes of type 1 diabetes observed in Caucasian patients are not found in Japanese patients, while protective HLA haplotypes are similar. Association studies of non-HLA genes have identified several candidate genes that influence the heterogeneity of disease phenotypes as well as disease susceptibility to type 1 diabetes. The INS-VNTR gene or polymorphisms of MICA gene are associated with susceptibility, whereas a certain allele of MICA gene and IL-10 gene polymorphism are associated with clinical heterogeneity of the disease. An expression of multiple autoantibodies to a biochemically determined autoantigen confers a high risk for progression to type 1 diabetes. The combined evaluation of multiple autoantibodies is more sensitive than is ICA testing for the diagnosis of type 1 diabetes. A high titer of GAD autoantibody has the predictive value of future insulin deficiency in patients with LADA. For accurate predictive strategies of future insulin deficiency, combinational multiple autoantibodies analysis or genetic determination should be considered for effective immune intervention.

CTLA4 gene polymorphism contributes to the mode of onset of diabetes with antiglutamic acid decarboxylase antibody in Japanese patients: genetic analysis of diabetic patients with antiglutamic acid decarboxylase antibody

AIM

The mode of onset is occasionally similar in Type 1 and Type 2 diabetes mellitus, and some patients with Type 2 diabetes are positive for antiglutamic acid decarboxylase antibody (GAD Ab). We investigated the contribution of Type 1 diabetes susceptibility genes to the progression of the insulin-deficient state and mode of onset of Type 2 diabetes in GAD Ab-positive (GAD-Ab+) patients. We examined the variable number of tandem repeats in the promoter region of the insulin gene (INS-VNTR, insulin-dependent diabetes mellitus (IDDM) 2) and cytotoxic T lymphocyte antigen 4 (CTLA4, IDDM12) as representative of Type 1 diabetes susceptibility genes.

METHODS

Patients with Type 2 diabetes who were GAD-Ab+ (n = 51) were selected for this study. In INS-VNTR, the class I allele was classified according to length (1S, 25-38 repeat units; 1M, 39-41 repeat units; 1L, 42-44 repeat units) and the exact class I allele length was analysed by specific polymerase chain reaction (PCR) amplifications. Analyses of classes II and III were performed by Southern blot. CTLA4 gene polymorphism (exon 1 position 49, G/A) was analysed by PCR-restriction fragment length polymorphism.

RESULTS

The distribution of INS-VNTR was no different between Type 1 diabetes and Type 2 diabetes with GAD Ab. The allele frequencies of CTLA4 gene polymorphism G and A in Type 2 diabetes/GAD-Ab+ were significantly different from those of Type 1 diabetes/GAD-Ab+ (G: 53%, A: 47% vs. G: 84%, A: 16%; P < 0.0001).

CONCLUSIONS

Our data showed that GAD-Ab+ Japanese patients presenting with Type 2 diabetes have shifted A allele while patients with abrupt onset have shifted G allele of CTLA4 gene polymorphism. Our results suggest that immunological function and polymorphism of the CTLA4 gene may contribute to the pathogenesis and progression of Type 1 diabetes.

Diabetes and nutrition: the mitochondrial part

Diabetes mellitus is the most common genetic disease in the Western world today. It is the phenotype for >150 genotypes. Each of these genotypes is characterized by impaired glucose tolerance and impaired control of intermediary metabolism. There are many strains of mice and rats that can be used to study diabetes in its various forms. One of these is the BHE/Cdb rat, which mimics the human phenotype with a mutation in the mitochondrial (mt) DNA. The result of such mutation is a loss in metabolic control with respect to the role of the mitochondria in this control. This review addresses those aspects of control that are exerted by mt oxidative phosphorylation (OXPHOS). Diet can have both genomic and nongenomic effects on OXPHOS. The type of dietary fat influences the fluidity of the mt membranes and hence, mt function. The dietary fat effect depends on the genetic background of the consumer. Diabetes-prone BHE/Cdb rats with base substitutions in the mt ATPase 6 gene are more likely to be influenced by the diet effect on mt membrane fluidity than are normal rats. Vitamin A also affects mt function through an effect on mt gene expression. BHE/Cdb rats have a greater need for vitamin A than normal rats and supplemental vitamin A appears to influence OXPHOS.

Genetic susceptibility factors of Type 1 diabetes in Asians

Type 1 diabetes is a multifactorial disease in which the insulin producing beta-cells of the pancreas are destroyed by the immune system, a process determined by the activity of major histocompatibility complex (MHC)-restricted T lymphocytes. Progress has been made in elucidating genetic factors involved in Type 1 diabetes in Caucasians, with less data available from Asia. For Asians, the human MHC locus (HLA region), especially the class II region, is the major susceptibility interval. The role of IDDM2, the insulin locus, has been questioned in Asia. In contrast to Caucasians, Asian populations have a very low incidence of Type 1 diabetes (0.4-1.1 cases/year/100 000 individuals). This low incidence rate in the Asian population may be related to the population frequency distribution of susceptible Type 1 diabetes genes, especially of HLA. The overall risk for Type 1 diabetes from HLA DR and DQ is determined by polymorphic residues (alleles) and particular combinations of alleles (haplotypes and genotypes) in a given individual. In Asians, it is very common that a protective DR4 allele is associated with susceptible DQ alleles while neutral/protective DQ alleles are associated with the susceptible DR4 alleles. Our analyses indicate that the counterbalancing between susceptible DRB1 and protective DQB1, and vice versa, is a factor that may contribute to the low incidence of diabetes in Asians. We find that identical HLA DRB1-DQB1 haplotypes of Asians and Caucasians have similar transmission to diabetic children and similar associations with diabetes. Moreover, the association with diabetes and transmission to a diabetic offspring of DR4 haplotypes varies depending on the haplotype borne on the homologous chromosome. This might contribute not only to the synergistic effect of DR3/4, but also to the susceptibility influence of DQB1*0401 haplotypes confined to DR4/X. High-risk DR4 subtypes were predominant in DR4/X, whereas protective DR4 subtypes were observed mainly in the DR3/4 genotype. Since in Asians DQB1*0401 is in linkage disequilibrium (LD) with DRB1*0405, we find more DRB1*0405-DQB1*0401 haplotypes in patients with DR4/X than in patients with DR3/4, suggesting that the contribution of the DRB1 locus may be greater in DR4/X than in DR3/4 genotypes. Several genome scans suggested additional susceptibility intervals and provided supporting evidence for several previously reported linkages. Other studies focused on the confirmation of linkage using multipoint sib-pair analyses with densely spaced markers and multiethnic collection of families. Although significant and consistent linkage evidence was reported for the susceptibility intervals IDDM12 (on 2q33) even in Asia, evidence for most other intervals varies in different data sets. LD mapping has become an increasingly important tool for both confirmation and fine-mapping of susceptibility intervals, as well as identification of etiological mutations. The examination of large and ethnically varied data sets including those of Asia has allowed identification of haplotypes that differ only at a single codon in a single locus. As more data become available, the study of pairs of haplotypes which differ at a single polymorphic site, but have different effects on disease susceptibility, should allow more precise definition of the polymorphisms involved in the disease process.

Higher resolution microplate array diagonal gel electrophoresis: application to a multiallelic minisatellite

The 5' polymorphic region of the insulin (INS, MIM# 176730) gene contains a variable tandem repetition of 14-15 bp (a variable number of tandem repeats (VNTR) locus). After PCR amplification, we achieved precise sizing of class I alleles (range 641 to 843 bp) on 96-well open-face polyacrylamide microplate array diagonal gel electrophoresis (MADGE) gels, obtaining resolution of the 2% mobility difference which represents one tandem repeat. PCR products were run double-stranded, but no additional bands were generated except in the case of differences of three, two, and one repeat between alleles; none compromised allele identification, and in the latter case the heteroduplex was a useful confirmation signal. No end labelling of primers was required, as the sensitive Vistra Green intercalating dye for double strands was used for visualization of bands from diluted samples. Duracryl, a high mechanical-strength polyacrylamide derivative, proved to have good resolution properties for electrophoresis. A co-run ladder ensured precise binning without inter-lane variability. Simultaneous electrophoresis of gels in a thermostatically controlled tank allowed up to 1,000 samples to be run in 90 min. Gels were analyzed using a FluorImager 595 fluorescent scanning system, and alleles identified using a combination of Phoretix software for band migration measurement and Microsoft Excel to compute allele sizes. Unlike other systems for minisatellite allele sizing, throughput was not limited (in time or cost) by electrophoresis.