Mats Sundvall

Genetic control of arthritis onset, severity and chronicity in a model for rheumatoid arthritis in rats

Rheumatoid arthritis (RA) is a chronic and genetically complex inflammatory disorder that leads to erosive destruction of peripheral joints. 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 course. 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.

The genetics of primary nocturnal enuresis: inheritance and suggestion of a second major gene on chromosome 12q.

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.

Genetic linkage analysis of collagen-induced arthritis in the mouse.

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.

The cotton-top tamarin revisited: Mhc class I polymorphism of wild tamarins, and polymorphism and allelic diversity of the class II DQA1, DQB1, and DRB loci

Cotton-top tamarins (Saguinus oedipus) in captivity are unusual in that they exhibit low levels of polymorphism and allelic diversity at the major histocompatibility complex (Mhc) class I loci. Since the polymorphism has previously only been examined in captive tamarins, we analyzed the Mhc class I alleles of a population of wild tamarins. These wild tamarins, like their captive counterparts, exhibited limited class I polymorphism. We also assessed the levels of polymorphism and allelic diversity at the Mhc class II DQA1, DQB1, DQB2, and the DRB loci in captive populations of cotton-top tamarins. In contrast to the extensive polymorphism in Old World monkeys, only two alleles were detected at each of DQA1 and DQB1. Also, the DQB2 locus was monomorphic and conserved between New and Old World monkeys. Sequences derived from four putative DRB loci were obtained, and extensive polymorphism was found at all four loci. Phylogenetic analysis did not indicate that any of the tamarin DRB loci, with the possible exception of Saoe-DRB3, were orthologous to the human DRB loci. At three of the DRB loci (Saoe-DRB11, Saoe-DRB*W12, Saoe-DRB*W22), the number of nonsynonymous changes was higher than the number of synonymous changes in the putative antigen recognition sites, indicative of positive selection. We found no support for a restriction on the polymorphism at the cotton-top tamarin class II loci. However, the allelic diversity at some of the Saoe-DRB loci is more limited than for the HLA-DRB1, consistent with a restriction imposed by the bone marrow-chimerical lifestyle.

A rapidly evolving region in the immunoglobulin heavy chain loci of rat and mouse: postulated role of (dC-dA)n.(dG-dT)n sequences.

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.

Linkage analysis of candidate loci in families with recurrent major depression

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.

Genetic mapping of loci for X-linked retinitis pigmentosa.

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.

Generation of Allelic Polymorphism at the DRB1 Locus of Primates by Exchange of Polymorphic Domains: A Plausible Hypothesis?

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.

Linkage analysis in properdin deficiency families: refined location in proximal Xp

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 θmax= 0.00) and DXS426 (Zmax= 12.9 at θmax= 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.

Genetic control of arthritis in rats

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.