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The genetic susceptibility to collagen-induced arthritis (CIA) in mice, the most commonly used model for rheumatoid arthritis, has been analyzed. The highly susceptible B10.RIII strain was crossed with the resistant RIIIS/J strain and the F2 intercross mice were subjected to genomic screening using microsatellite markers. These strains share the MHC region on chromosome 17, known to be of importance in CIA (this locus is named Mcia1). The same cross has earlier been used to map the major genes outside the MHC controlling chronic relapsing experimental allergic encephalomyelitis (EAE). It was found that the major locus controlling CIA (Mcia2; lod 4.12) was located on chromosome 3 in the same region as one of the major loci controlling EAE (Eae3). The linkage was reproduced in a mouse strain in which the locus was isolated on the B10.RIII background at the N4I2 generation. A second putative locus was identified on chromosome 13 (lod 3.13). The present finding identifies new loci outside the MHC controlling CIA and provides evidence that mouse CIA is controlled by polymorphic genes.

Multiple sclerosis (MS) is a chronic inflammatory disorder characterized by multifocal damage of myelin in the central nervous system (CNS). The prevalence of this putative autoimmune disease is 0.1% in individuals of northern European origin. Family, adoption and twin studies implicate genetic factors in the aetiology. MS is widely speculated to be a multifactorial disorder with a complex mode of inheritance. Despite many studies of candidate genes, only an association with HLA-DR2-DQ6 has been generally detected, and the number of susceptibility genes remains unknown. The chronic variant of experimental allergic encephalomyelitis (EAE), a T-cell mediated autoimmune disease in rodents, represents a relevant animal model for MS given the chronic relapsing disease course and inflammatory changes of CNS observed in these demyelinating disorders. Susceptibility to EAE is also influenced by the major histocompatibility complex (MHC). Human syntenic regions to murine loci predisposing to EAE were tested as candidate regions for genetic susceptibility of MS. Three chromosomal regions (1p22-q23, 5p14-p12 and Xq13.2-q22) were screened in 21 Finnish multiplex MS families most originating from a high risk region in western Finland. Several markers yielded positive lod scores on 5p14-p12, syntenic to the murine locus Eae2. Our data provide evidence for a predisposing locus for MS on 5p14-p12.

The evolution of polymorphism at the Mhc class II DPB1 locus was studied by comparison of chimpanzee (Pan troglodytes), pygmy chimpanzee (Pan paniscus), gorilla (Gorilla gorilla) and human DPB1 alleles. Extensive polymorphism was found in all hominoids. The clustering of sequences in the phylogenetic tree is consistent with rapid generation of the DPB1 polymorphism. Analysis of the substitution pattern for human alleles shows an excess of non-synonymous changes to synonymous changes at antigen recognition sites, indicating that the amino acid polymorphism at these sites is being maintained by selection. By contrast, no excess of nonsynonymous changes was found at the antigen recognition sites of nonhuman hominoid species. Thus, it appears that diversifying selection on the DPB1 polymorphism has intensified in the lineage leading to humans. No evidence was found for the existence of ancient allelic lineages predating the divergence of the hominoid species. The number of synonymous differences among DPB1 alleles is lower than among DQB1 and DRB1 alleles, indicative of a more recent origin for the DPB1 polymorphism and consistent with the more rapid evolution suggested by the phylogenetic tree.

The loci encoding the class II cell surface antigens HLA-DR, -DQ, and -DP exhibit a remarkable degree of allelic polymorphism. Most of the class II allelic diversity is localized to the second exon, which encodes a beta-pleated sheet followed by an alpha-helical domain. Here, phylogenetic analysis of 39 human DRB1 alleles and 21 DRB1 alleles obtained by polymerase chain reaction (PCR) amplification from a set of closely related primates reveals that sequences encoding the beta-pleated sheet and those encoding the alpha-helix of the second domain have different evolutionary histories. The polymorphisms in the beta-pleated sheet have been conserved between species and appear to reflect the ancestral relationships among haplotypes, whereas polymorphic segments encoding the alpha-helical domain appear to have been inserted by interallelic sequence exchange into the framework of different ancestral DRB1 sequences. Allelic polymorphism at the DRB1 locus may thus have been generated in part by combining different variants of the two structural domains.

Rheumatoid arthritis (RA) is a chronic and genetically complex inflammatory disorder that leads to erosive destruction of peripheral joints1,2,3,4,5. The use of animal models mimicking RA, such as pristane-induced arthritis (PIA) in rats, should facilitate its genetic analysis. Pristane is a non-immunogenic synthetic oil that, after a single subcutaneous injection into DA rats, induces arthritis restricted to peripheral joints with a chronic relapsing disease course6. To identify genes involved in the control of chronic arthritis, we made crosses between susceptible DA rats and resistant E3 rats and analysed the progeny with microsatellite markers covering the entire rat genome. Our results show that different arthritis phenotypes are associated with different chromosomal loci. Loci on chromosomes 4 and 6 ( Pia2 and Pia3 ) influence arthritis onset, whereas a locus on chromosome 12 ( Pia4 ) is associated with severity and joint erosion. We found that chronicity is associated with a different set of loci, one on chromosome 4 and the other on chromosome 14 ( Pia5, Pia6 ). These findings demonstrate for the first time that different phases of a chronic self-perpetuative disease which mimics RA are associated with distinct sets of genes.

Recurrent major depression, RMD, is characterized by the occurrence of depressive episodes in the absence of mania and/or hypomania. In linkage studies, RMD (or, in general, unipolar depression) are frequently grouped together with bipolar illnesses into a broad definition of affective disorders. However, twin studies suggest that RMD and bipolar disorders might have different genetic determinants. The objective of this study was to test a set of families with RMD for linkage to chromosomes that have been recently proposed to contain susceptibility loci for bipolar disorders: chromosomes 16, 18, 21 and the short arm of chromosome 4. We analysed five large families from the northern part of Sweden ascertained through a proband with RMD and containing several patients with RMD. For the genetic analysis, we included only severely affected individuals (those who had at least three episodes that required medical treatment) to increase the chances of finding a larger degree of genetic determination. The genetic model led to a total disease prevalence of 5% in females and 3% in males. We did not find significant evidence for linkage to any of the candidate chromosomes in the combined family set. Only one of the families showed a slight indication for linkage with markers from the pericentromeric region of chromosome 18. A genome scan analysis on an extended collaborative family material with severely affected individuals with RMD should be performed to evaluate whether RMD and bipolar disorders have a different genetic etiology.

Primary nocturnal enuresis (PNE), or bedwetting at night, affects approximately 10% of 6 year old children. Genetic components contribute to the pathogenesis and recently one locus was assigned to chromosome 13q. We evaluated the genetic factors and the pattern of inheritance for PNE in 392 families. Dominant transmission was observed in 43% and an apparent recessive mode of inheritance was observed in 9% of the families. Among the 392 probands the ratio of males to females was 3:1 indicating sex linked or sex influenced factors. Linkage to candidate regions was tested in 16 larger families segregating for autosomal dominant PNE. A gene for PNE was excluded from chromosome 13q in 11 families, whereas linkage to the interval D13S263-D13S291 was suggested (Zmax = 2.1) in three families. Further linkage analyses excluded about 1/3 of the genome at a 10 cM resolution except the region around D12S80 on chromosome 12q that showed a positive two point lod score in six of the families (Zmax = 4.2). This locus remains suggestive because the material was not sufficiently large to give evidence for heterogeneity. Our pedigree analysis indicates that major genes are involved in a large proportion of PNE families and the linkage results suggest that such a gene is located on chromosome 12q.

B10.RIII mice develop chronic and relapsing experimental autoimmune encephalomyelitis (EAE) after immunization with the myelin basic protein (MBP) peptide 89-101. The disease is associated with the major histocompatibility complex (MHC) (eae1). We have now investigated the importance of non-MHC regions for the EAE susceptibility in a cross between RIIIS/J and B10.RIII mice which share the MHC region but differ in disease susceptibility. Linkage analysis using microsatellite markers spanning the genome identified a region (eae2) on chromosome 15 which showed linkage to disease (P = 0.0002). Our data also suggest linkage to a second region (eae3) on chromosome 3 (P = 0.0024), and provide evidence for locus interactions between eae2 and eae3. These results provide clues to the genetic basis of multiple sclerosis.

Properdin is a component of the alternative activation pathway of the complement system. Deficiency or dysfunction of the protein is inherited in an X-linked recessive manner. Affected males have an increased risk of developing meningococcal disease. Six multi-generation families with different types of properdin deficiency were analyzed using microsatellite and other polymorphisms on the X chromosome. Based on multipoint data, it was found that the disease gene maps close to DXS255 (Zmax = 13.3 at theta max = 0.00) and DXS426 (Zmax = 12.9 at theta max = 0.00) on the Xp-arm near the centromere. There was no indication of genetic heterogeneity among the six families analyzed. Thus it is now possible to perform accurate DNA-based determination of the inheritance of the mutation in affected families.

Linkage analysis was performed in three Swedish families segregating for X-linked retinitis pigmentosa (XLRP), using five polymorphic DNA markers assigned to Xp. Individual recombination events were analyzed and two- and five-point linkage analysis was undertaken. In one family, a XLRP locus was mapped to the same position as OTC corresponding to RP3. In two families, a disease locus linked to OTC was excluded. In one family, recombination events indicate a locus for XLRP outside the interval (DXS84-OTC-DXS255-DXS14), most likely on the centromeric side of DXS14.

The allelic polymorphism at the DRB1 locus of chimpanzee and gorilla was studied by nucleotide sequence analysis of amplified genomic fragments from the second exon. None of the combinations of polymorphic motifs found on chimpanzee and gorilla alleles have similar allelic counterparts in humans, indicating that many HLA-DRB1 alleles have been generated since the divergence of the three hominoid species. Phylogenetic tree analysis of different parts of the second exon indicate that allelic variation at the DRB1 locus could have been generated in part by inter-allelic and inter-locus sequence exchanges. A putative point for such exchange is located at the transition point between sequences encoding the s- sheet and those encoding one of the α-helices. These results imply that allelic variation in the β-sheet of the antigen is conserved between species, while the part encoding one of the α-helices has accumulated a number of species specific residues. The segments of genes encoding parts of the DR antigen involved in the peptide binding, and those encoding parts involved in the interaction with the T-cell receptor, may thus be under different selection pressures.

The nucleotide sequences of the introns that are located between the C4 exon and the first membrane exon of mouse and rat immunoglobulin epsilon-chain genes have been determined. The rat intron sequence was found to contain four separate clusters of repetitive sequences all of which consisted of (dC-dA)n.(dG-dT)n dinucleotide repeats. A comparison between this chromosomal region in mouse and rat revealed four deletions or duplications, three of which have occurred inside or at the borders of the CA clusters. Rearrangements have occurred inside or at the borders of all four repeats after the evolutionary separation of mouse and rat. The sequence comparison reveals in addition a duplication, connected to the CA repeats, which has occurred early in evolution, before the evolutionary divergence of mouse and rat. These findings suggest that (dC-dA)n.(dG-dT)n sequences are potential targets for recombination events.

Summary This study was specifically designed to analyse the genetic control of the chronic disease course for the development of arthritis. Arthritis models with a chronic erosive arthritis are collagen induced arthritis induced with homologous collagen in oil but also arthritis induced with certain non-immunogenic adjuvants such as pristane and avridine. In the presently described experiment we have used pristane induced arthritis. A single injection of 150 μl pristane induces severe chronic arthritis in DA rats. The disease mimics rheumatoid arthritis in many aspects such as the chronic disease course, an erosive inflammation of peripheral joints, symmetric involvement of the joints and the development of rheumatoid factors. To determine the genetic contribution we have used a number of inbred, recombinant inbred and congenic strains as well as specifically designed segregating crosses. An influence by the MHC region (designated Pia1 locus) on the chronic disease course was determined through the uses of MHC congenic LEW strains in which the RT1-f haplotype conferred highest susceptibility. To map genes outside of MHC we used an F2 cross between the highly susceptible DA and the resistant E3 strains. Loci exclusively associated with different phenotypes of the disease could be identified: Arthritis onset ( Pia2 and Pia3 ). Severity and joint erosions ( Pia4 ). Chronicity ( Pia5 and Pia6 ) and Pia1 (determined from MHC congenic (strains) These findings demonstrates that a chronic self-perpetuative disease, mimicking rheumatoid arthritis, is controlled by different set of genes exclusively linked to different phases of the disease course such as arthritis onset, joint erosions, severity and chronicity.