HLA typing in families with multiple cases of rheumatoid arthritis

Relative predispositional effects and mode of inheritance of HLA-DRB1 alleles among community-based Caucasian females with rheumatoid arthritis

Multiple HLA-DRB1 alleles encoding a shared epitope (SE) at amino acid positions 70-74 are associated with susceptibility to rheumatoid arthritis (RA). However, the nature of the association and the mode of inheritance differ depending upon the source of RA patients and laboratory methodology. We studied the relative predispositional effects (RPE) and mode of inheritance of DRB1 alleles among a community-based sample of 180 RA patients and 116 healthy controls, all Caucasian females. Polymerase chain reaction (PCR)-based assays were used for DRB1 genotyping, and the genotypic distributions were analyzed by both the RPE and antigen genotype frequency among patients (AGFAP) methods. We examined the evidence of synergy among DRB1 alleles for RA risk by comparing the observed DRB1 genotype distribution to that predicted under Hardy-Weinberg equilibrium. Fifty-six percent of RA cases were attributable to DRB1 alleles encoding the SE. The RPEs of DRB1 alleles were *0401 > *0404 > *1001 > *0408 > *0101. The strength of the RA association was not significantly different for these alleles. The AGFAP analysis was consistent with a recessive mode of inheritance for DRB alleles, while an additive (dominant) model was rejected. We found no evidence of synergy for RA risk among individual DRB1 alleles based on comparison of the observed vs. predicted genotype distributions. These results suggest that among community-based Caucasian females with RA, the DRB1 RA susceptibility gene influences disease risk in a recessive fashion without synergy among individual DRB1 alleles.

Sex influences on the penetrance of HLA shared-epitope genotypes for rheumatoid arthritis

The association between rheumatoid arthritis (RA) and HLA DRB1 alleles may arise through linkage disequilibrium with a disease locus or the direct involvement of HLA alleles in RA. In support of the latter possibility, the shared-epitope hypothesis has been postulated, stating that conformationally similar DR beta chains encoded by several DRB1 alleles confer disease susceptibility. To examine these alternative hypotheses of marker-disease association and to investigate gender differences in RA susceptibility, we analyzed the distributions of PCR-based DRB1 genotypes of 309 Caucasian RA patients and 283 Caucasian controls. Initially, the marker-association-segregation chi 2 method was used to evaluate evidence for linkage disequilibrium and the direct involvement of markers DR4 Dw4, DR4 Dw14, and DR1 in RA susceptibility. Additional shared-epitope models that grouped DRB1 alleles into five classes (*0401, *0404/*0102, *0405/*0408/*0101, *1001, and all others) and postulated relationships between genotypes and RA susceptibility were also fitted to observed genotypic distributions by the method of minimal chi 2. For females, a linkage-disequilibrium model provided a good fit to the data, as did a shared-epitope model with RA most penetrant among individuals with the *0401,*0401 genotype. For males, the best model indicated highest RA penetrance among shared-epitope compound heterozygotes. Clinically, male RA patients had more subcutaneous nodules and greater use of slowly acting antirheumatic drugs, while female RA patients had earlier disease onset. This study therefore suggests that sex-related factors influence the RA penetrance associated with DRB1 shared-epitope genotypes and that DRB1 effects on RA prognosis and pathogenesis should be considered separately for men and women.

The genotypic distribution of shared-epitope DRB1 alleles suggests a recessive mode of inheritance of the rheumatoid arthritis disease-susceptibility gene

OBJECTIVE

To test whether the genotypic distribution of rheumatoid arthritis (RA)-associated DRB1 alleles suggests that the DRB1-associated disease-susceptibility gene has a recessive or additive (dominant) mode of inheritance.

METHODS

Caucasian patients with RA and control subjects were recruited from a faculty outpatient practice. DRB1 typing was done by several DNA-based techniques: polymerase chain reaction (PCR), followed by dot-blot hybridization with sequence-specific oligonucleotides, conventional and PCR-based restriction fragment length polymorphisms (RFLPs), and a multiplex amplification-refractory mutation RFLP system. The genotypic distribution of shared-epitope DRB1 alleles was analyzed by antigen genotype frequency among patients. The analytical method postulates a linkage-disequilibrium model with a disease locus close to a marker locus and a marker allele in linkage disequilibrium with the disease-susceptibility allele. In this instance, the marker allele was defined alternatively by any DR4-group allele, by any DR4-group or DR1-group allele, by any DR4-group shared-epitope allele, by any DR4-group shared-epitope allele plus DRB1*0101, or by any shared-epitope DRB1 allele. Observed numbers were compared with those predicted for recessive mode or additive (dominant) mode of inheritance of the DRB1-associated RA disease-susceptibility gene.

RESULTS

The genotypic distribution of shared-epitope DRB1 alleles (DRB1*0401, *0404, *0405, *0408, *0101, *0102, or *1001) fit that predicted for a recessive mode of inheritance and was significantly different from that predicted for an additive (dominant) mode. When the analysis was restricted to shared-epitope DR4 alleles alone (DRB1*0401, *0404, *0405, or *0408), the observed genotype numbers fit the recessive mode best. When DR1-group alleles were added to DR4-group alleles, or alternatively, when the major shared-epitope DR1 allele (*0101) was added to DR4-group shared-epitope alleles, there was a less significant deviation from the additive mode of inheritance. The reason for this was derived by comparison of observed genotype frequencies to those expected under Hardy-Weinberg equilibrium; there was a deficit of persons with DRB1*0401, *0101 and an excess of *0101,X.

CONCLUSION

The genotypic distribution of shared-epitope DRB1 marker alleles suggests that the mode of inheritance of the DRB1-associated disease susceptibility gene must be recessive and not additive (dominant).

HLA-linked susceptibility to rheumatoid arthritis. A study of forty-one multicase families from northern India

OBJECTIVE

To analyze segregation of rheumatoid arthritis (RA) with HLA-DR4 and/or other alleles in multicase RA families and to compare the segregation patterns among affected and unaffected sibs.

METHODS

Forty-one multicase families (22 multiplex and 19 simplex) of northern Indian origin were studied for HLA haplotype segregation.

RESULTS

HLA haplotype sharing among affected sibs was observed more often than expected in families in which both parents were healthy (P < 0.05). RA cosegregated with a DR4 haplotype among offspring only in multiplex families in which both parents were unaffected (P < 0.05), while in simplex families, the disease segregated with DR4 only when the allele was from the affected DR4-heterozygous parent. In DR4-negative affected sib pairs, DR1, DR6, and DR10 were inherited from healthy parents more often than expected.

CONCLUSION

Dissimilar modes of inheritance are seen among multiplex and simplex RA families. The results of segregation analysis are compatible with the hypothesis that an epitope, rather than an individual DR antigen(s), is responsible for increased risk for development of RA.

Occurrence of autoimmune diseases and relationship of autoantibody expression with HLA phenotypes in multicase rheumatoid arthritis families

Presence of autoimmune diseases and relationship of autoantibody expression with HLA association has been studied in 44 multicase rheumatoid arthritis (RA) families of Asian Indian origin. An increased prevalence of systemic lupus erythematosus (SLE) was observed in relatives (2.3%). Although HLA-DR4 segregated preferentially with seropositivity in general, no difference was observed among seropositive versus seronegative RA. On the other hand, no HLA association was observed with ANF positivity in these families. An increased frequency of DR7 in the ANF negative and RF negative group of RA patients compared to positive groups suggests that it may act as protective element for the development of autoantibodies in RA. An increased occurrence of DR4 in relatives affected with SLE was observed. While RA segregated mostly with HLA-DR4 in these families, autoimmune thyroid disease and insulin dependent diabetes mellitus (IDDM) segregated with HLA-DR3 suggesting the involvement of at least two sets of HLA-linked autoimmunity favouring susceptibility genes in the Indian population.

HLA haplotype sharing in rheumatoid arthritis sibships: risk estimates in siblings

The distribution of the number of parental HLA haplotypes shared by sibs with rheumatoid arthritis (RA) has been used to obtain information on the genetics of the disease. Thirty-four RA sibships (25 sib-pairs, 9 sib-trios) were ascertained, all of which were HLA typed and which satisfied the 1958 American Rheumatism Association criteria for "definite" RA. These were combined with other published but nonoverlapping data from the literature; thus, 143 sib-pairs, 36 sib-trios and 4 sibquads were identified. The affected RA sibs shared two, one and zero parental HLA haplotypes in a ratio of 40: 45: 15 which was significantly different from random expectations (p less than 0.05). Risk estimates for sibs of probands for those sharing two, one and zero parental HLA haplotypes were 6.2%, 3.5% and 2.3% respectively. Risks subdivided by DR genotype of the proband are also calculated, the highest (8.7%) being for sibs sharing two haplotypes with a proband carrying at least one DR4 allele. The manuscript also considers genetic information in relatives other than siblings; an extension of the affected relative pair haplotype sharing method to second and third degree kinships is presented.