HLA-linked susceptibility to rheumatoid arthritis in north India

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-DR1 and DRw6 association in DR4-negative rheumatoid arthritis patients

This study of 110 seropositive rheumatoid arthritis (RA) patients confirms the significant association of susceptibility to RA with HLA-DR4 specificity (P less than 0.001). The DR1 frequency is elevated in the entire seropositive patient group, reaching marginal significance (P less than 0.025). The DR4-negative patients, however, have a much higher prevalence of DR1 (P less than 0.001). Surprisingly, the DRw6 specificity is significantly increased in the remaining DR4- and DR1-negative patients (P less than 0.01). These results demonstrate that RA is not associated with a single HLA-specificity, but to various degrees with DR4, DR1, and DRw6. These findings, and particularly the newly recognized association with DRw6, support the hypothesis that functionally equivalent shared epitopes or conformations on otherwise distinct MHC molecules may confer risk for developing RA.