Chromosome 14 markers in rheumatoid arthritis

Two-loci interaction confirms arthritis-regulating quantitative trait locus on rat chromosome 6

A form of genetic interaction, or epistasis, occurs when one gene interferes with the phenotypic effect of another nonallelic gene. In pristane-induced arthritis (PIA) in rats we have previously identified Pia3, on chromosome 6, to be a locus that regulates onset of disease. In a single congenic strain containing Pia3 on the arthritis-susceptible DA background, DA.Pia3, no difference in onset of disease or early disease severity could be detected. After a two-loci interaction analysis of (E3 x DA)F2 intercross data, Pia3 was found to interact with Pia4 (chromosome 12). Subsequently, the DA.Pia3 congenic strain was combined with the DA.Pia4 congenic strain so that an effect of Pia3 could be observed. The effect of heterozygosity in Pia4 results in lower severity and thus in combination with Pia3 made it possible to observe that Pia3 alleles from the arthritis-resistant E3 strain rendered more severe arthritis into the otherwise 100% susceptible DA strain. As the introduction of Pia4 heterozygosity results in a lower level of arthritis severity we regard this as an additive interaction with a severity threshold-lowering effect.

Alpha-1-antitrypsin phenotypes and associated disease patterns in neurological patients

INTRODUCTION

Alpha-1-antitrypsin (AAT) deficiency is usually associated with lung or liver disease. It is often detected as a qualitative reduction of the alpha-1 band on the serum protein electrophoretic pattern.

MATERIAL AND METHODS

We examined the protein electrophoretic pattern in sera of 22980 unselected consecutive patients with neurological disorders and noted a reduced alpha-1 band in 88. Their phenotypes were compared with the clinical disease.

RESULTS

75 patients had a deficient or non-M and 13 the usual MM phenotype. Contrary to in the general population, PiMZ was four times more common than PiMS. Vascular disease was more common in patients with PiMZ while multiple sclerosis significantly more frequent in patients with PiMS than with other phenotypes, including PiMM.

CONCLUSIONS

Other genetic abnormalities have previously been found in AAT associated with multiple sclerosis, but not PiMS. Since PIMS leads to modest reduction of AAT activity, the association may be through other mechanisms than reduced protease activity.

Immunoglobulin allotypes (GM and KM) and their interactions with HLA antigens in autoimmune diseases: a review

GM and KM immunoglobulin (Ig) allotypes and their interactions with HLA antigens have been analyzed in various autoimmune diseases: multiple sclerosis, rheumatoid arthritis, insulin-dependent diabetes mellitus (IDDM), systemic lupus erythematosus, coeliac disease, Crohn's disease, Graves' disease, atrophic thyroiditis, Hashimoto's thyroiditis, myasthenia gravis, chronic active hepatitis, alopecia areata, uveitis, vitiligo, Turner's syndrome, glomerular nephritis, Berger's disease and idiopathic dilated cardiomyopathy. This review reports published results about associations or linkages, as well as the origins of the populations, the numbers of patients and controls tested. The possible role of Ig polymorphisms in the physiopathology of autoimmune diseases is discussed. Ig allotypes and statistical methods used to analyse the HLA and Ig data are also described.

HLA-linked rheumatoid arthritis

Twenty-eight pedigrees were ascertained through pairs of first-degree relatives diagnosed with rheumatoid arthritis (RA). RA was confirmed in 77 pedigree members including probands; the absence of disease was verified in an additional 261 pedigree members. Pedigree members were serologically typed for HLA. We used likelihood analysis to statistically characterize the HLA-linked RA susceptibility locus. The genetic model assumed tight linkage to HLA. The analysis supported the existence of an HLA-linked RA susceptibility locus, estimated the susceptibility allele frequency as 2.16%, and estimated the lifetime penetrance as 41% in male homozygotes and as 48% in female homozygotes. Inheritance was recessive in males and was nearly recessive in females. In addition, the analysis attributed 78% of the variance within genotypes to genetic or environmental effects shared by siblings. The genetic model inferred in this analysis is consistent with previous association, linkage, and familial aggregation studies of RA. The inferred HLA-linked RA susceptibility locus accounts for approximately one-half of familial RA, although it accounts for only approximately one-fifth of the RA in the population. Although other genes may account for the remaining familial RA, a large portion of RA cases may occur sporadically.

Immunoglobulin kappa genotype confers risk of rheumatoid arthritis among HLA-DR4 negative individuals

Because DNA polymorphisms of immunoglobulin kappa confer risk for rheumatoid arthritis (RA) and not all persons with RA have the HLA-DR4 marker, genomic polymorphisms of immunoglobulin kappa and HLA-DR beta were determined in white patients with RA. Compared with control subjects matched for DR beta genotype, the homozygous genotype of the constant segment of immunoglobulin kappa (C kappa) was more frequent in the subgroups of RA patients without the DR beta genotype corresponding to HLA-DR4 (relative risk 6.2, P less than 0.01) and patients without DR4 or DR1 (relative risk 6.7, P = 0.013), but not in the DR4+ RA subgroup. Therefore, RA may be a genetically heterogeneous disease, with HLA-DR4 marking one genetic subset and the homozygous C kappa genotype marking another.

The contribution of HLA to rheumatoid arthritis

The contribution of genes within the major histocompatibility complex to rheumatoid arthritis has been calculated (Rotter & Landaw 1984). Separate data from hospital- and population-based studies of monozygotic twin concordance rates and sibling recurrence risks have been used, along with material from published haplotype-sharing studies. Using either source of information gives the same result, a contribution of 37%.

DNA polymorphism of immunoglobulin kappa confers risk of rheumatoid arthritis

To examine the hypothesis that a hereditary factor linked to the immunoglobulin kappa constant segment (C kappa) contributes to risk of rheumatoid arthritis (RA), white persons with RA were examined for Sac I restriction site polymorphisms. RA patients were more likely to have the 5/5-kb C kappa genotype than white control subjects (relative risk 2.8, P less than 0.02). A subgroup of RA patients who were positive for serum rheumatoid factor had a relative risk of 2.4 (P less than 0.05). The subgroup without serum rheumatoid factor had an even higher relative risk of 9.7 (P less than 0.05). The results suggest that immunoglobulin kappa is an important component in the genetic predisposition toward RA.