Development of an integrated genome informatics, data management and workflow infrastructure: a toolbox for the study of complex disease genetics.

The genetic dissection of complex disease remains a significant challenge. Sample-tracking and the recording, processing and storage of high-throughput laboratory data with public domain data, require integration of databases, genome informatics and genetic analyses in an easily updated and scaleable format. To find genes involved in multifactorial diseases such as type 1 diabetes (T1D), chromosome regions are defined based on functional candidate gene content, linkage information from humans and animal model mapping information. For each region, genomic information is extracted from Ensembl, converted and loaded into ACeDB for manual gene annotation. Homology information is examined using ACeDB tools and the gene structure verified. Manually curated genes are extracted from ACeDB and read into the feature database, which holds relevant local genomic feature data and an audit trail of laboratory investigations. Public domain information, manually curated genes, polymorphisms, primers, linkage and association analyses, with links to our genotyping database, are shown in Gbrowse. This system scales to include genetic, statistical, quality control (QC) and biological data such as expression analyses of RNA or protein, all linked from a genomics integrative display. Our system is applicable to any genetic study of complex disease, of either large or small scale.

Replication of an association between the lymphoid tyrosine phosphatase locus (LYP/PTPN22) with type 1 diabetes, and evidence for its role as a general autoimmunity locus.

In the genetic analysis of common, multifactorial diseases, such as type 1 diabetes, true positive irrefutable linkage and association results have been rare to date. Recently, it has been reported that a single nucleotide polymorphism (SNP), 1858C>T, in the gene PTPN22, encoding Arg620Trp in the lymphoid protein tyrosine phosphatase (LYP), which has been shown to be a negative regulator of T-cell activation, is associated with an increased risk of type 1 diabetes. Here, we have replicated these findings in 1,388 type 1 diabetic families and in a collection of 1,599 case and 1,718 control subjects, confirming the association of the PTPN22 locus with type 1 diabetes (family-based relative risk (RR) 1.67 [95% CI 1.46-1.91], and case-control odds ratio (OR) 1.78 [95% CI 1.54-2.06]; overall P = 6.02 x 10(-27)). We also report evidence for an association of Trp(620) with another autoimmune disorder, Graves' disease, in 1,734 case and control subjects (P = 6.24 x 10(-4); OR 1.43 [95% CI 1.17-1.76]). Taken together, these results indicate a more general association of the PTPN22 locus with autoimmune disease.

Investigating the utility of combining phi29 whole genome amplification and highly multiplexed single nucleotide polymorphism BeadArray genotyping.

BACKGROUND: Sustainable DNA resources and reliable high-throughput genotyping methods are required for large-scale, long-term genetic association studies. In the genetic dissection of common disease it is now recognised that thousands of samples and hundreds of thousands of markers, mostly single nucleotide polymorphisms (SNPs), will have to be analysed. In order to achieve these aims, both an ability to boost quantities of archived DNA and to genotype at low costs are highly desirable. We have investigated phi29 polymerase Multiple Displacement Amplification (MDA)-generated DNA product (MDA product), in combination with highly multiplexed BeadArray genotyping technology. As part of a large-scale BeadArray genotyping experiment we made a direct comparison of genotyping data generated from MDA product with that from genomic DNA (gDNA) templates. RESULTS: Eighty-six MDA product and the corresponding 86 gDNA samples were genotyped at 345 SNPs and a concordance rate of 98.8% was achieved. The BeadArray sample exclusion rate, blind to sample type, was 10.5% for MDA product compared to 5.8% for gDNA. CONCLUSIONS: We conclude that the BeadArray technology successfully produces high quality genotyping data from MDA product. The combination of these technologies improves the feasibility and efficiency of mapping common disease susceptibility genes despite limited stocks of gDNA samples.

Lack of association of the Ala(45)Thr polymorphism and other common variants of the NeuroD gene with type 1 diabetes.

Variation in genes necessary for normal functioning and development of beta-cells, e.g., NEUROD1, which encodes a transcription factor for the insulin gene and is important in beta-cell development, causes maturity-onset diabetes of the young. Some studies have reported an association between a nonsynonymous Ala(45)Thr (+182G-->A) single nucleotide polymorphism (SNP) in NEUROD1 and type 1 diabetes, but this result has not been consistently found. To clarify this, we genotyped Ala(45)Thr in 2,434 type 1 diabetic families of European descent and Caucasian ethnicity from five different countries. Taking the allele frequency of 36% for Thr(45) and an odds ratio (OR) of 1.2, this sample provided >99% power to detect an association (P < 0.05). We could not confirm the association (P = 0.77). No evidence of population heterogeneity in the lack of association of Thr(45) with type 1 diabetes was observed. To evaluate the possibility that another NEUROD1 variant was associated with type 1 diabetes, we resequenced the gene in 32 U.K. affected individuals and identified and genotyped all common SNPs (minor allele frequency >10%; n = 5) in 786 families. We report no evidence of association of these common variants in NEUROD1 and type 1 diabetes in these samples.

Analysis of the type 2 diabetes-associated single nucleotide polymorphisms in the genes IRS1, KCNJ11, and PPARG2 in type 1 diabetes.

It has been proposed that type 1 and 2 diabetes might share common pathophysiological pathways and, to some extent, genetic background. However, to date there has been no convincing data to establish a molecular genetic link between them. We have genotyped three single nucleotide polymorphisms associated with type 2 diabetes in a large type 1 diabetic family collection of European descent: Gly972Arg in the insulin receptor substrate 1 (IRS1) gene, Glu23Lys in the potassium inwardly-rectifying channel gene (KCNJ11), and Pro12Ala in the peroxisome proliferative-activated receptor gamma2 gene (PPARG2). We were unable to confirm a recently published association of the IRS1 Gly972Arg variant with type 1 diabetes. Moreover, KCNJ11 Glu23Lys showed no association with type 1 diabetes (P > 0.05). However, the PPARG2 Pro12Ala variant showed evidence of association (RR 1.15, 95% CI 1.04-1.28, P = 0.008). Additional studies need to be conducted to confirm this result.

Haplotype tag single nucleotide polymorphism analysis of the human orthologues of the rat type 1 diabetes genes Ian4 (Lyp/Iddm1) and Cblb.

The diabetes-prone BioBreeding (BB) and Komeda diabetes-prone (KDP) rats are both spontaneous animal models of human autoimmune, T-cell-associated type 1 diabetes. Both resemble the human disease, and consequently, susceptibility genes for diabetes found in these two strains can be considered as potential candidate genes in humans. Recently, a frameshift deletion in Ian4, a member of the immune-associated nucleotide (Ian)-related gene family, has been shown to map to BB rat Iddm1. In the KDP rat, a nonsense mutation in the T-cell regulatory gene, Cblb, has been described as a major susceptibility locus. Following a strategy of examining the human orthologues of susceptibility genes identified in animal models for association with type 1 diabetes, we identified single nucleotide polymorphisms (SNPs) from each gene by resequencing PCR product from at least 32 type 1 diabetic patients. Haplotype tag SNPs (htSNPs) were selected and genotyped in 754 affected sib-pair families from the U.K. and U.S. Evaluation of disease association by a multilocus transmission/disequilibrium test (TDT) gave a P value of 0.484 for IAN4L1 and 0.692 for CBLB, suggesting that neither gene influences susceptibility to common alleles of human type 1 diabetes in these populations.

Association of the T-cell regulatory gene CTLA4 with susceptibility to autoimmune disease.

Genes and mechanisms involved in common complex diseases, such as the autoimmune disorders that affect approximately 5% of the population, remain obscure. Here we identify polymorphisms of the cytotoxic T lymphocyte antigen 4 gene (CTLA4)--which encodes a vital negative regulatory molecule of the immune system--as candidates for primary determinants of risk of the common autoimmune disorders Graves' disease, autoimmune hypothyroidism and type 1 diabetes. In humans, disease susceptibility was mapped to a non-coding 6.1 kb 3' region of CTLA4, the common allelic variation of which was correlated with lower messenger RNA levels of the soluble alternative splice form of CTLA4. In the mouse model of type 1 diabetes, susceptibility was also associated with variation in CTLA-4 gene splicing with reduced production of a splice form encoding a molecule lacking the CD80/CD86 ligand-binding domain. Genetic mapping of variants conferring a small disease risk can identify pathways in complex disorders, as exemplified by our discovery of inherited, quantitative alterations of CTLA4 contributing to autoimmune tissue destruction.

Linkage and association mapping of the LRP5 locus on chromosome 11q13 in type 1 diabetes.

Linkage of chromosome 11q13 to type 1 diabetes (T1D) was first reported from genome scans (Davies et al. 1994; Hashimoto et al. 1994) resulting in P <2.2 x 10(-5) (Luo et al. 1996) and designated IDDM4 ( insulin dependent diabetes mellitus 4). Association mapping under the linkage peak using 12 polymorphic microsatellite markers suggested some evidence of association with a two-marker haplotype, D11S1917*03-H0570POLYA*02, which was under-transmitted to affected siblings and over-transmitted to unaffected siblings ( P=1.5 x 10(-6)) (Nakagawa et al. 1998). Others have reported evidence for T1D association of the microsatellite marker D11S987, which is approximately 100 kb proximal to D11S1917 (Eckenrode et al. 2000). We have sequenced a 400-kb interval surrounding these loci and identified four genes, including the low-density lipoprotein receptor related protein (LRP5) gene, which has been considered as a functional candidate gene for T1D (Hey et al. 1998; Twells et al. 2001). Consequently, we have developed a comprehensive SNP map of the LRP5 gene region, and identified 95 SNPs encompassing 269 kb of genomic DNA, characterised the LD in the region and haplotypes (Twells et al. 2003). Here, we present our refined linkage curve of the IDDM4 region, comprising 32 microsatellite markers and 12 SNPs, providing a peak MLS=2.58, P=5 x 10(-4), at LRP5 g.17646G>T. The disease association data, largely focused in the LRP5 region with 1,106 T1D families, provided no further evidence for disease association at LRP5 or at D11S987. A second dataset, comprising 1,569 families from Finland, failed to replicate our previous findings at LRP5. The continued search for the variants of the putative IDDM4 locus will greatly benefit from the future development of a haplotype map of the genome.