HLA class II distribution in Congolese with hyperthyroidism: preliminary results

OBJECTIVE: Incidence of the hyperthyroidism is continuously increasing, whereas our knowledge concerning the facilitating or etiologic factors of this increase are still partial. To evaluate some of these unknown factors, we started this preliminary study, in order to identify HLA genes in hyperthyroid Congolese, and to determine their susceptibilty in the appearance and development of hyperthyroidism at the Hospital Clinic of Kinshasa. MATERIALS AND METHODS: Nine Congolese women with hyperthyroidism, and thirteen healthy controls (3 women and 10 men) were examined and compared for HLA-DR and HLA-DQ genes analyses, from August 2000 to August 2002. DRB1 and DQB1 alleles were identified, using the Polymerase Chain Reaction (PCR) and immobilized sequence-specific oligonucleotide (SSO HLA-DRB1 and DQB1 test) probes assays. RESULTS: In the group with hyperthyroidism, three alleles (HLA-DR1, HLA-DR2, HLA-DR3) and an allele group (HLA-DR11,13,14) were found for DRB1 locus, while only one allele (HLA-DQB1*0602) was identified for DQB1 locus; allele group HLA-DR11,13,14 was the most frequent (allele frequency=0.50), followed by HLA-DR3 allele (allele frequency=0.222); 6 haplotypes were observed, with predominance of haplotype DR3/DR11,13,14 (genotype frequency=0.333), followed by haplotype DR11,13,14/DR11,13,14-DQB1*0602 (genotype frequency=0.222). In the group of healthy controls, three alleles (HLA-DR2, HLA-DR3, HLA-DR4) and an allele group (HLA-DR11,13,14) were identified for DRB1; HLA-DR2 allele was predominant (allele frequency=0.615), followed by allele group HLA-DR11,13,14 (allele frequency=0.231); a statistic significant difference was observed between the frequencies of DR2 allele and allele group DR11,13,14 in the healthy controls compared to those of hyperthyroid patients (p=0.02); 6 haplotypes were also detected in this group, the most frequent haplotype being HLA-DR2/DR2-DQB1*0602 (genotype frequency=0.540 versus 0.333 in the hyperthyroid group) (p=0.048). HLA-DQB1*0602 was dominant in the healthy controls group (allele frequency=0.890), versus HLA-DQB1*0302 (allele frequency=0.110). CONCLUSIONS: HLA-DR2, HLA-DQB1*0602 and DR2/DR2-DQB1*0.602 would play a protective role against the hyperthyroidism, while DR3 allele, allele group DR11,13,14 and haplotype HLA-DR3/DR11,13,14 would predispose to this disease or to Graves' exophtalmopathy. A large and profound study is needed to confirm our preliminary results.