Transgenic rescue implicates beta2-microglobulin as a diabetes susceptibility gene in nonobese diabetic (NOD) mice.

Type 1 diabetes in both humans and nonobese diabetic (NOD) mice results from T-cell-mediated autoimmune destruction of insulin-producing pancreatic beta cells. Linkage studies have shown that type 1 diabetes in NOD mice is a polygenic disease involving more than 15 chromosomal susceptibility regions. Despite extensive investigation, the identification of individual susceptibility genes either within or outside the major histocompatibility complex region has proven problematic because of the limitations of linkage analysis. In this paper, we provide evidence implicating a single diabetes susceptibility gene, which lies outside the major histocompatibility complex region. Using allelic reconstitution by transgenic rescue, we show that NOD mice expressing the beta(2) microglobulin (beta(2)M)(a) allele develop diabetes, whereas NOD mice expressing a murine beta(2)M(b) or human allele are protected. The murine beta(2)M(a) allele differs from the beta(2)M(b) allele only at a single amino acid. Mechanistic studies indicate that the absence of the NOD beta(2)M(a) isoform on nonhematopoietic cells inhibits the development or activation of diabetogenic T cells.

Autoreactive diabetogenic T-cells in NOD mice can efficiently expand from a greatly reduced precursor pool.

A broad repertoire of pancreatic beta-cell autoreactive T-cells normally contributes to the development of type 1 diabetes in NOD mice. However, it has been unknown if a large reduction in the precursor pool from which autoreactive T-cells are drawn would inhibit the development of type 1 diabetes. To address this issue, we reduced the precursor frequency of autoreactive T-cells in NOD mice through allelic exclusion induced by transgenic expression of an H2-Db class I-restricted T-cell receptor (TCR) specific for a pathologically irrelevant lymphocytic choriomeningitis virus (LCMV) peptide. TCR allelic exclusion greatly reduced the pool of T-cells from which diabetogenic effectors could be derived in these NODxLCMV TCR Tg mice. Surprisingly, this did not impair their type 1 diabetes susceptibility. Furthermore, a diabetogenic CD8 T-cell population that is prevalent in standard NOD mice was present at essentially equivalent levels in pancreatic islets of NODxLCMV TCR Tg mice. Other data indicated that the antigenic specificity of these CD8 T-cells is primarily the function of a shared TCR-alpha chain. Although the percentage of TCR transgenic T-cells decreased in NOD versus B6,D2 control mice, much higher total numbers of both the TCR transgenic and the nontransgenic T-cells accumulated in the NOD strain. This transgenic T-cell accumulation in the absence of the cognate peptide indicated that the NOD genetic background preferentially promotes a highly efficient antigen-independent T-cell expansion. This might allow diabetogenic T-cells in NOD mice to undergo an efficient expansion before encountering antigen, which would represent an important and previously unconsidered aspect of pathogenesis.

Axonemal beta heavy chain dynein DNAH9: cDNA sequence, genomic structure, and investigation of its role in primary ciliary dyskinesia.

Dyneins are multisubunit protein complexes that couple ATPase activity with conformational changes. They are involved in the cytoplasmatic movement of organelles (cytoplasmic dyneins) and the bending of cilia and flagella (axonemal dyneins). Here we present the first complete cDNA and genomic sequences of a human axonemal dynein beta heavy chain gene, DNAH9, which maps to 17p12. The 14-kb-long cDNA is divided into 69 exons spread over 390 kb. The cDNA sequence of DNAH9 was determined using a combination of methods including 5' rapid amplification of cDNA ends, RT-PCR, and cDNA library screening. RT-PCR using nasal epithelium and testis RNA revealed several alternatively spliced transcripts. The genomic structure was determined using three overlapping BACs sequenced by the Whitehead Institute/MIT Center for Genome Research. The predicted protein, of 4486 amino acids, is highly homologous to sea urchin axonemal beta heavy chain dyneins (67% identity). It consists of an N-terminal stem and a globular C-terminus containing the four P-loops that constitute the motor domain. Lack of proper ciliary and flagellar movement characterizes primary ciliary dyskinesia (PCD), a genetically heterogeneous autosomal recessive disorder with respiratory tract infections, bronchiectasis, male subfertility, and, in 50% of cases, situs inversus (Kartagener syndrome, KS). Dyneins are excellent candidate genes for PCD and KS because in over 50% of cases the ultrastructural defects of cilia are related to the dynein complex. Genotype analysis was performed in 31 PCD families with two or more affected siblings using a highly informative dinucleotide polymorphism located in intron 26 of DNAH9. Two families with concordant inheritance of DNAH9 alleles in affected individuals were observed. A mutation search was performed in these two "candidate families," but only polymorphic variants were found. In the absence of pathogenic mutations, the DNAH9 gene has been excluded as being responsible for autosomal recessive PCD in these families.

Fine-mapping of the type 1 diabetes locus (IDDM4) on chromosome 11q and evaluation of two candidate genes (FADD and GALN) by affected sibpair and linkage-disequilibrium analyses.

Previous studies have identified a susceptibility region for insulin-dependent (type 1) diabetes mellitus on chromosome 11q13 (IDDM4). In this study, 15 polymorphic markers were analyzed for 382 affected sibpair (ASP) families with type 1 diabetes. Our analyses provided additional evidence for linkage for IDDM4 (a peak LOD score of 3.4 at D11S913). The markers with strong linkage evidence are located within an interval of approximately 6 cM between D11S4205 and GALN. We also identified polymorphisms in two candidate genes, Fas-associated death domain protein (FADD) and galanin (GALN). Analyses of the data by transmission/disequilibrium test (TDT) and extended TDT (ETDT) did not provide any evidence for association/linkage with these candidate genes. However, ETDT did reveal significant association/linkage with the marker D11S987 (P=0.0004) within the IDDM4 interval defined by ASP analyses, suggesting that IDDM4 may be in the close proximity of D11S987.

Genetic and physical mapping of a type 1 diabetes susceptibility gene (IDDM12) to a 100-kb phagemid artificial chromosome clone containing D2S72-CTLA4-D2S105 on chromosome 2q33.

Polymorphic markers within the CTLA4 gene on chromosome 2q33 have been shown to be associated with type 1 diabetes. Therefore, a gene responsible for the disease (IDDM12) most likely lies within a region of <1-2 cM of CTLA4. To define more precisely the IDDM12 interval, we genotyped a multiethnic (U.S. Caucasian, Mexican-American, French, Spanish, Korean, and Chinese) collection of 178 simplex and 350 multiplex families for 10 polymorphic markers within a genomic interval of approximately 300 kb, which contains the candidate genes CTLA4 and CD28. The order of these markers (D2S346, CD28, GGAA19E07, D2S307, D2S72, CTLA4, D2S105, and GATA52A04) was determined by sequence tagged site content mapping of bacterial artificial chromosome (BAC) and yeast artificial chromosome (YAC) clones. The transmission disequilibrium test (TDT) analyses of our data revealed significant association/linkage with three markers within CTLA4 and two immediate flanking markers (D2S72 and D2S105) on each side of CTLA4 but not with more distant markers including the candidate gene CD28. Tsp analyses revealed significant association only with the three polymorphic markers within the CTLA4 gene. The markers linked and associated with type 1 diabetes are contained within a phagemid artificial chromosome clone of 100 kb, suggesting that the IDDM12 locus is either CTLA4 or an unknown gene in very close proximity.

IL4 and IL4Ralpha genes are not linked or associated with type 1 diabetes.

Previous studies have shown the immunoregulatory functions IL-4 in type 1 diabetes mellitus. Therefore, the genes involved in the IL-4 regulatory pathway are candidates for diabetes susceptibility genes. Here we have evaluated IL4 and the alpha subunit of the IL-4 receptor (IL4Ralpha) genes using the affected sibpair (ASP) and transmission/disequilibrium test (TDT). We analyzed 309 diabetic families from the United States and 87 families from various European countries. There was no evidence that either of these two genes are linked or associated with type 1 diabetes. Means by which IL-4 directed signals could indirectly alter diabetes susceptibility are proposed.

Chromosomal localization and complete genomic sequence of the murine autoimmune regulator gene (Aire).

We have recently cloned the murine autoimmune regulator (Aire) gene, the homologue of human AIRE responsible for the autoimmune polyglandular syndrome type 1 (APS1) or autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED). Here, we report the genomic sequence (18,413 bp) for the entire Aire gene and its 5' flanking region, which contains putative regulatory sequences. Comparison of the genomic and cDNA sequences indicates that the Aire gene is composed of 14 exons and the coding sequence shares high similarities between mouse and human. The sizes of the homologous introns in the two species are conserved; however, the introns do not share significant sequence homologies except the sequences near the splice donor and acceptor sites. Sequence analyses of the 5' regulatory region and the complete coding region in three mouse strains (B6, NOD and SJL) did not reveal any sequence variation, suggesting sequence conservation between different inbred mouse strains. Using one of the six microsatellite markers identified by genomic sequencing and a B6 x Cast backcross mapping panel, we mapped the mouse Aire gene to chromosome 10, a syntenic region containing the Cdl18 and Pfkl genes on human chromosome 21q22.

Genetic homogeneity, high-resolution mapping, and mutation analysis of the urofacial (Ochoa) syndrome and exclusion of the glutamate oxaloacetate transaminase gene (GOT1) in the critical region as the disease gene.

The urofacial (Ochoa) syndrome (UFS) is a rare autosomal recessive disorder characterized by abnormal facial expression and urinary abnormalities. Previously, we mapped the gene to a genomic interval of approximately 1 cM on chromosome region 10q23-24, using families from Columbia. Here we demonstrate genetic homogeneity of the syndrome through homozygosity mapping in American patients with Irish heritage. We established a physical map and identified novel polymorphic markers in the UFS critical region. Haplotype analysis using the new markers mapped the UFS gene within one YAC clone of 1,410 kb. We also determined the precise location of the gene encoding for glutamate oxaloacetate transaminase (GOT1) within the new UFS critical region and determined its genomic structure. However, mutation analysis excluded GOT1 as a candidate for the UFS gene.

The IDDMK(1,2)22 retrovirus is not detectable in either mRNA or genomic DNA from patients with type 1 diabetes.

A new viral sequence (IDDMK(1,2)22) similar to the human endogenous retrovirus (HERV)-K10/K18 subfamilies has recently been isolated from the culture supernatants of leukocyte-infiltrated islets from two patients who died at the onset of type 1 diabetes. It was claimed that this endogenous retrovirus is expressed in patients with type 1 diabetes but not in healthy control subjects, suggesting an important role of the retrovirus in beta-cell-specific autoimmunity that results in type 1 diabetes. However, despite exhaustive attempts involving identical and expanded methods of detection, we did not observe the IDDMK(1,2)22 viral sequence in genomic DNA, lymphocyte, or plasma RNA in any subject. Therefore, we believe that the viral sequence is not derived from an endogenous retrovirus and that a role for the retrovirus in the pathogenesis of type 1 diabetes must be reconsidered.

Genetic susceptibility factors in type 1 diabetes: linkage, disequilibrium and functional analyses.

Continuing progress has been made in elucidating the genetic factors involved in type 1 diabetes (insulin-dependent diabetes mellitus [IDDM]) in the past year. Two 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 sibpair analyses with densely spaced markers and multiethnic collections of families. Although significant and consistent linkage evidence was reported for the susceptibility intervals IDDM8 (on human chromosome 6q27), IDDM4 (on 11q) and IDDM5 (on 6q25), evidence for most other intervals varies in different data sets -probably due to a weak effect of the disease genes, genetic heterogeneity or random variation. Linkage disequilibrium mapping has become an increasingly important tool for both the confirmation and fine-mapping of susceptibility intervals, as well as identification of etiological mutations. Functional studies indicate, firstly, that the susceptible and protective HLA class II molecules HLA-DR and -DQ bind and present nonoverlapping peptides and, secondly, that the variable number of tandem repeats at the 5' end of the insulin gene (susceptibility interval IDDM2) regulates insulin expression in the thymus.

Insulin-dependent diabetes mellitus (IDDM) is associated with CTLA4 polymorphisms in multiple ethnic groups.

Linkage disequilibrium (association) analysis was used to evaluate a candidate region near the CTLA4/CD28 genes using a multi-ethnic collection of families with one or more children affected by IDDM. In the data set unique to this study (Spanish, French, Mexican-American, Chinese and Korean), the transmission/disequilibrium test (TDT) revealed a highly significant deviation for transmission of alleles at the (AT)n microsatellite marker in the 3' untranslated region (P = 0.002) and the A/G polymorphism in the first exon (P = 0.00002) of the CTLA4 gene. The overall evidence for transmission deviation of the CTLA4 A/G alleles is also highly significant (P = 0.00005) in the combined data set (669 multiplex and 357 simplex families) from this study and a previous report on families from USA, Italy, UK, Spain and Sardinia. Significant heterogeneity was observed in these data sets. The British, Sardinian and Chinese data sets did not show any deviation for the A/G polymorphism, while the Caucasian-American data set showed a weak transmission deviation. Strong deviation for transmission was seen in the three Mediterranean-European populations (Italian, Spanish and French) (P = 10(-5)), the Mexican-American population (P = 0.002) and the Korean population (P = 0.03). These results suggest that a true IDDM susceptibility locus (designated IDDM12) is located near CTLA4.