No association of vitamin D intake or 25-hydroxyvitamin D levels in childhood with risk of islet autoimmunity and type 1 diabetes: the Diabetes Autoimmunity Study in the Young (DAISY)

AIMS/HYPOTHESIS

The aim of the study was to investigate the association between vitamin D intake and status and the risk of islet autoimmunity (IA) and subsequent type 1 diabetes in children at increased risk of type 1 diabetes.

METHODS

The Diabetes Autoimmunity Study in the Young (DAISY) in Denver, CO, USA, has been following children at increased risk of diabetes since 1993. As of February 2011, 198 children developed IA during follow-up of 2,644 DAISY children. Vitamin D intake and plasma 25-hydroxyvitamin D [25(OH)D] were measured longitudinally. Proportional hazards regression analyses of time to IA, or type 1 diabetes in IA-positive children, were conducted, with vitamin D intake and 25(OH)D as time-varying covariates. HRs were calculated for a standard deviation difference in exposure, with adjustment for confounders.

RESULTS

Intake of vitamin D was not associated with the risk of IA (adjusted HR 1.13; 95% CI 0.95, 1.35; p = 0.18) nor progression to diabetes in IA-positive children (adjusted HR 1.30; 95% CI 0.91, 1.86; p = 0.15). Moreover, 25(OH)D level was not associated with the risk of IA (adjusted HR 1.12; 95% CI 0.88, 1.43; p = 0.36), nor progression to diabetes in IA-positive children (adjusted HR 0.91; 95% CI 0.68, 1.22; p = 0.54). In the 128 children in whom we measured 25(OH)D at 9 months of age, 25(OH)D was not associated with risk of IA (n = 30 IA-positive children) (adjusted HR 1.02; 95% CI 0.96, 1.07; p = 0.58).

CONCLUSIONS/INTERPRETATION

Neither vitamin D intake nor 25(OH)D levels throughout childhood were associated with the risk of IA or progression to type 1 diabetes in our population.

Associations between the human MHC and sustained virologic response in the treatment of chronic hepatitis C virus infection

The human major histocompatability complex (MHC) genes encode the human leukocyte antigens, which are important in antigen presentation and regulation of CD8+ and CD4+ T cells. Response to therapies in hepatitis C virus (HCV) infection is highly variable (30-80%) and lower response rates have been reported among African Americans (AA; approximately 30%) compared to Caucasian Americans (CA; approximately 50%) infected with genotype-1 viruses. We evaluated whether MHC gene variants were associated with response to therapy and racial differences in AA and CA sustained virologic response (SVR) rates. We genotyped alleles at 8 MHC loci: 3 class I (A, B and C) and 5 class II (DRB1, DQA1, DQB1, DPA1 and DPB1) loci in 373 individuals (179 AA and 194 CA) with genotype-1 HCV infections, who were treated with peginterferon-alpha-2a and ribavirin. We observed carriage of A(*)02 (RR=1.33(1.08-1.64); P=0.008), B(*)58 (RR=1.84(1.24-2.73); P=0.002) and DPB1(*)1701 (RR=1.57(1.09-2.26); P=0.015) to be associated with SVR after adjustment for other predictors of response. In analysis of AA and CA subgroups separately, we observed potential, though not statistically significant, differences in these MHC associations. Variation in the immunogenetic background of HCV-infected individuals might account for some observed variation in viral-specific immunity and courses of disease. In this regard, future studies examining broader patient populations are warranted.

Similar incidence of type 1 diabetes in two ethnically different populations (Italy and Slovenia) is sustained by similar HLA susceptible/protective haplotype frequencies

The incidence of type 1 diabetes (T1DM) seems to depend in part on the population frequencies of susceptible and protective HLA haplotypes. The present study aimed to (i): characterize the genetic susceptibility to T1DM in the Slovenian population, (ii) test the general hypothesis that T1DM incidence is related to the frequencies of susceptible/protective haplotypes, (iii) compare allele, haplotype and genotype frequencies in Slovenians and Italians that represent two white populations with a similar incidence of T1DM (7.9/100,000/year and 8.1/100,000/year, respectively). The haplotype found most frequently among Slovenian T1DM patients was DRB1*0301-DQA1*0501-DQB1*0201 (53%). The DR4-DQA1*0301-DQB1*0302 haplotypes conferring susceptibility to T1DM were those bearing DRB1*0401 (OR = 12), DRB1*0404 (OR = 4.7) and DRB1*0402 (OR = 4.5). Negative associations with the disease were found for the following haplotypes: DRB1*1501-DQA1*0102-DQB1*0602, DRB1*1301-DQA1*0102-DQB1*0603, DRB1*1101/1104-DQA1*0501-DQB1*0301, and DRB1*1401-DQA1*0101-DQB1*0503. Our findings indicate that the low frequencies of susceptible genotypes, in particular, DR3-DQA1*0501-DQB1*0201/DR4-DQA1*0301-DQB1*0302, together with a high frequency of protective haplotypes, could in part explain the low incidence of T1DM in the Slovenian population. The combined frequencies of susceptible genotypes were similar in the two populations (Slovenia = 19.2%, Italy = 17.6%), and the 95% confidence limits of the OR values for each genotype in the two populations overlapped, indicating no significant differences between the values. We conclude that the similar incidences of T1DM in Italian and Slovenian populations are in part a reflection of similar frequencies of HLA susceptible/protective haplotypes.

Evidence for oligogenic inheritance of type 1 diabetes in a large Bedouin Arab family

Based on a genomic search for linkage, a locus contributing to type 1 diabetes in a large Bedouin Arab family (19 affected relatives) maps to the long arm of chromosome 10 (10q25; nonparametric linkage = 4.99; P = 0.00004). All affected relatives carry one or two high-risk HLA-DR3 haplotypes that are rarely found in other family members. One chromosome 10 haplotype, the B haplotype, was transmitted from a heterozygous parent to 13 of 13 affected offspring compared to 10 of 23 unaffected siblings. Recombination events occurring on this haplotype place the susceptibility locus in an 8-cM interval between markers D10S1750 and D10S1773. Two adjacent markers, D10S592 and D10S554, showed evidence of linkage disequilibrium with the disease locus. A 273-bp allele at D10S592 was transmitted to 8 of 10 affected offspring compared to 3 of 14 unaffected siblings, and a 151-bp allele at D10S554 was transmitted to 15 of 15 affected offspring compared with 10 of 24 unaffected siblings. D10S554 and D10S592 and the closest flanking markers are contained in a 1,240-kb yeast artificial chromosome, a region small enough to proceed with positional cloning.

Evidence of HLA class II association with antibody response against the malaria vaccine SPF66 in a naturally exposed population

The antibody response against the malaria vaccine SPf66 and against circumsporozoite (CS) protein has been tested in immune adults from a malaria endemic area in Papua New Guinea. All individuals were genotyped for the HLA class II DQB1 and DRB1 loci, and the humoral response was analyzed with respect to the identified class II alleles. At each locus, only three alleles were frequent, namely DRB1*11, *15, and *16, and DQB1*0301, *0502, and *0601. Antibodies against SPf66 and CS protein were found in 84% and 79% of the individuals, respectively. A strong negative association was detected between the humoral response against SPf66 and DRB1*15 and DQB1*0601. A positive association of the response was observed with DRB1*11 and DQB1*0301. After analysis with a multiple regression model in which all alleles were included simultaneously, only DRB1*15 remained significantly associated with low antibody responses. This suggests that nonresponders may be expected after immunization with SPf66 in certain populations.

Higher autoantibody levels and recognition of a linear NH2-terminal epitope in the autoantigen GAD65, distinguish stiff-man syndrome from insulin-dependent diabetes mellitus

The smaller form of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD65) is a major autoantigen in two human diseases that affect its principal sites of expression. Thus, destruction of pancreatic beta cells, which results in insulin-dependent diabetes mellitus (IDDM), and impairment of GABA-ergic synaptic transmission in Stiff-Man syndrome (SMS) are both characterized by circulating autoantibodies to GAD65. Anti-GAD65 autoantibodies in IDDM are predominantly directed to conformational epitopes. Here we report the characterization of humoral autoimmune responses to GAD65 in 35 SMS patients, of whom 13 (37%) also had IDDM. All SMS patients immunoprecipitated native GAD65 and the main titers were orders of magnitude higher than in IDDM patients. Furthermore, in contrast to the situation in IDDM, autoantibodies in 35 of 35 (100%) of SMS patients recognized denatured GAD65 on Western blots. Two major patterns of epitope specificity were identified on Western blots. The first pattern, detected in 25 of 35 SMS patients (71%), of whom 11 had IDDM (44%), was predominantly reactive with a linear NH2-terminal epitope residing in the first eight amino acids of GAD65. Nine of nine individuals who were HLA-haplotyped in this group carried an IDDM susceptibility haplotype and HLA-DR3, DQw2 was particularly abundant. The second pattern, detected in 10 of 35 patients (29%) of whom two had IDDM (20%), included reactivity with the NH2-terminal epitope plus strong reactivity with one or more additional epitope(s) residing COOH-terminal to amino acid 101. The second epitope pattern may represent epitope spreading in the GAD65 molecule, but may also include some cases of epitope recognition associated with IDDM resistant HLA-haplotypes. The principal NH2-terminal linear epitope in GAD65 distinguishes the reactivity of SMS and IDDM autoantibodies and may be a determinant of pathogenicity for GABA-ergic neurons. The greater magnitude and distinct specificity of the humoral response to GAD65 in SMS may reflect a biased involvement of the T helper cell type 2 (Th2) subset of CD4+ T cells and antibody responses, whereas IDDM is likely mediated by the Th1 subset of CD4+ T cells and cytotoxic T cell responses.

Two subsets of HLA-DQA1 alleles mark phenotypic variation in levels of insulin autoantibodies in first degree relatives at risk for insulin-dependent diabetes

Levels of insulin autoantibodies (IAA) vary among different first degree relatives of insulin-dependent diabetes mellitus patients, suggesting genetic regulation. We previously reported elevated IAA among DR4-positive at risk relatives. In this study, 72/82 at risk relatives were IAA positive, of whom 75% (54/72) carried DR4 versus 20% (2/10) of IAA-negative relatives (P = 0.0004). However, 69% (18/26) of DR4-negative relatives were IAA positive. Since DR4 did not account for all IAA positivity, we analyzed DQA1 and DQB1 alleles. Homozygosity for DQA1 alleles deriving from the evolutionary lineage 4 (*0401, *0501, *0601) was associated with low IAA levels, while lineage 1-3 alleles (*0101, *0102, *0103, *0201, *0301) correlated with higher levels. Most (93%, 65/70) relatives with lineage 1-3 alleles were IAA positive (mean = 360 +/- 63 SEM nU/ml). Only 7/12 relatives homozygous for lineage 4 alleles were IAA-positive, with lower levels than relatives with lineage 1-3 alleles (mean = 55 +/- 15 SEM nU/ml, P < 0.0001; 7/12 vs 65/70, P = 0.004). The amino acid sequences of lineage 1-3 alleles uniquely share glutamic acid (E) and phenylalanine (F) at positions 40 and 51 (EF alleles). Lineage 4 alleles have glycine (G) and leucine (L) at those positions (GL alleles). 90% (65/72) of IAA-positive relatives had an EF allele, while only 75% (54/72) had DR4 (P = 0.01). Homozygosity for GL alleles (often DQA1 *0501 on DR3 haplotypes) correlated with little or no humoral response to insulin. Thus, HLA-DQB1 GL alleles, or other genes on haplotypes (e.g., DR3) that carry these DQA1 alleles, may confer recessive low responsiveness to insulin.

Association of HLA-DQB1*0201 with stiff-man syndrome

Stiff-man syndrome (SMS) is a rare disorder of the central nervous system of probable autoimmune origin. Patients with SMS often have other autoimmune diseases, in particular type I (insulin-dependent) diabetes mellitus (IDDM). Approximately 60% of patients with SMS have high titers of autoantibodies against the enzyme glutamic acid decarboxylase. Similar to SMS, the majority of patients with IDDM have autoantibodies against glutamic acid decarboxylase at or before diabetes onset, although usually at a lower titer and with a different reaction pattern than patients with SMS. To investigate the immunogenetic basis of SMS, we HLA-typed 18 patients with the disease. Seventy-two percent carried the DQB1*0201 allele (13 of 18, P = 0.02 vs. 18 of 48 controls), indicating that SMS is associated with this allele. DQB1*0201 is also a susceptibility allele for IDDM and other autoimmune diseases. Patients with SMS carried the IDDM-protective DQB1*0602 allele and other sequence-related DQB1*06 alleles with the same frequency observed in controls. In contrast, these alleles are rarely found in IDDM. Five of 8 (62.5%) SMS patients lacking a DQB1*06 allele were diabetic in contrast to only 2 of 10 (20%) with a DQB1*06 allele (P = 0.08), suggesting that the presence of DQB1*0602 or other DQB1*06 alleles may be associated with a reduced prevalence of diabetes among patients with SMS.

Analysis of HLA class II polymorphism using polymerase chain reaction

A simple, rapid, and precise method of typing HLA class II polymorphism would be valuable in the areas of disease susceptibility, tissue transplantation, individual identification, and anthropological genetics. Herein, we describe a method of analyzing class II sequence polymorphism based on polymerase chain reaction (PCR) amplification and hybridization with oligonucleotide probes. Many more DNA-defined alleles at the class II loci have been identified than can be distinguished by conventional serologic typing. Consequently, matching transplant donors and recipients by PCR/oligonucleotide typing should reduce graft rejection and graft-vs-host disease. Also, the ability to identify alleles conferring genetic predisposition to specific diseases (eg, insulin-dependent diabetes mellitus) is significantly enhanced by distinguishing the many alleles or "subtypes" within a serologic type (eg, DR4). One valuable property of sequence-based HLA typing strategies, like oligonucleotide probe hybridization, is that they reveal how and where two alleles differ, not simply that they can be operationally distinguished. The nature and location of HLA polymorphisms appears to be critical in disease association studies and are important in tissue typing for transplantation. New alleles at the DRB1, DPB1, and DQB1 loci are likely to be identified as this technology is applied to more and more samples, particularly in nonwhite ethnic groups. A new allele is uncovered as an unusual pattern of probe binding and then confirmed by sequencing. This pattern is observed because class II polymorphism is localized to specific regions and virtually all "new" alleles represent "shuffled" combinations of polymorphic sequences found in previously known alleles. Since these polymorphisms are in the region of probe binding, these new alleles can be detected without increasing the probe panel. Obviously, any new allele with a new polymorphic sequence in a region for which typing probes are not available would not be revealed by oligonucleotide typing. With the PCR primers and probes described here, 7 DQ alpha 1 alleles, 15 DQ beta 1 alleles, 18 DPB1 alleles, and 32 DRB1 alleles are distinguished. Additional primers and/or probes can, of course, increase the allelic discrimination of PCR/oligonucleotide probe typing. These horseradish peroxidase-labeled oligonucleotide probes are stable (> 2 years when stored at 4 degrees C) and the typing system is simple and robust. Although this dot blot/oligonucleotide hybridization procedure is a powerful and precise method of HLA class II typing, the complexity of the procedure increases as the number of probes required for analysis increases.(ABSTRACT TRUNCATED AT 400 WORDS)

HLA class II alleles and susceptibility and resistance to insulin dependent diabetes mellitus in Mexican-American families

The role of HLA class II alleles in genetic predisposition to insulin dependent diabetes mellitus (IDDM) was examined by PCR/oligonucleotide probe typing of 42 Mexican-American IDDM families derived from Hispanic Caucasians and Native Americans. All high risk haplotypes (HLA-DR3 and DR4) were of European origin while the most strongly protective haplotype (DRB1*1402) was Native American. Of the 16 DR-DQ DR4 haplotypes identified, only those bearing DQB1*0302 conferred risk; the DRB1 allele, however, also markedly influenced IDDM risk. The general pattern of neutral and protective haplotypes indicates that the presence of Asp-57 in the HLA-DQ beta chain does not confer IDDM protection per se and indicates that both DRB1 and DQB1 influence IDDM susceptibility as well as protection.

HLA-DR, DQ and DP typing using PCR amplification and immobilized probes

A simple, rapid, and precise method of typing HLA class II polymorphism would be valuable in the areas of disease susceptibility, tissue transplantation, individual identification and anthropological genetics. Here we describe a method of analysing class II sequence polymorphism based on polymerase chain reaction (PCR) amplification and hybridization with oligonucleotide probes. One valuable property of sequence-based HLA typing strategies, like oligonucleotide probe hybridization, is that they reveal how and where two alleles differ, not simply that they can be operationally distinguished. The nature and location of HLA polymorphisms appears to be critical in disease association studies and are likely to be important in tissue typing for transplantation. New alleles at the DRB1, DPB1 and DQB1 loci are likely to be identified as this technology is applied to more and more samples, particularly in non-Caucasian ethnic groups. A new allele is uncovered as an unusual pattern of probe binding and then confirmed by sequencing. This pattern is observed because class II polymorphism is localized to specific regions and virtually all 'new' alleles have polymorphisms in the region of probe binding. Obviously, any new allele with a new polymorphic sequence in a region for which typing probes are not available would not be revealed by oligonucleotide typing. With the PCR primers and probes described here, 7 DQA1 alleles, 15 DQB1 alleles, 18 DPB1 alleles, and 32 DRB1 alleles are distinguished. Additional primers and/or probes can, of course, increase the allelic discrimination of oligonucleotide dot blot typing. These horseradish peroxidase (HRP)-labelled oligonucleotide probes are stable (greater than 2 years when stored at 4 degrees C) and the typing system is simple and robust. Over 500 samples from the CEPH pedigrees (unpublished data; A. B. Begovich, et al., manuscript in preparation) and greater than 1000 unrelated samples have been typed by this procedure. Although this dot blot/oligonucleotide hybridization procedure is a powerful and precise method of HLA class II typing, the complexity of the procedure increases as the number of probes required for analysis increases. The reverse dot blot method, based on an array of immobilized probes, allows the typing of individual samples in one single hybridization reaction. In this approach, a panel of unlabelled oligonucleotides are immobilized to a nylon membrane. The PCR product is labelled during the amplification reaction by using biotinylated primers and hybridized to the membrane. The presence of bound PCR product specifically hybridized to a given probe is detected using streptavidin-HRP conjugates and either chromogenic or chemiluminescent substrates.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular analysis of HLA class I and class II antigen loss mutants reveals a homozygous deletion of the DR, DQ, and part of the DP region: implications for class II gene order

The mutant human B-lymphoblastoid cell lines, 721.174 and 721.180, previously reported to exhibit greatly reduced expression of human HLA class I and II antigens (DeMars et al., Hum Immunol 11:77, 1984), were analyzed by Southern blotting using class II cDNA and genomic clones as hybridization probes. All genomic sequences complementary to DR alpha, DR beta, DQ alpha, and DQ beta probes were absent from these mutants. DZ alpha genomic sequences were deleted as were the DP alpha 1 and DP beta 1 loci but the DP beta 2 and most, if not all, of the DP alpha 2 locus were retained. However, no RNA transcripts for either DP alpha 2 or DP beta 2 could be detected. The mapping of the deletion breakpoint within the DP cluster allows the orientation of the loci in the DP region with respect to the centromere as follows: centromere, DP beta 2, DP beta 1, DP alpha 1, (DQ, DR). In addition, the analysis of a set of DR-, DQ-, DP+ homozygous deletion mutants (721.82, 721.84, and 721.101) reveals a deletion breakpoint between the DQ alpha 1/DQ beta 1 loci and the DQ alpha 2/DQ beta 2 loci. These mutants retain DZ alpha genomic sequences, tentatively mapping the DZ alpha locus between the DQ and the DP region. The residual ability of the DR-, DQ-, DP- mutants (174 and 180)* to stimulate allogeneic and autologous lymphoproliferative responses must be attributed to expression of as yet unidentified class II antigens, or to non-class II antigens.