Molecular genetics of MHC class II alleles in Chinese patients with IgA nephropathy

We have studied the restriction fragment length polymorphism (RFLP) of the major histocompatibility complex (MHC) class II DQ and DR regions of 79 Chinese patients with IgA nephropathy (IgAN) and compared it with 104 normal Chinese controls. The DR and DQ alleles were confirmed by polymerase chain reaction using sequence specific primers. There was a significantly higher frequency of homozygous DQ beta 3b (DQ7) in patients with IgAN (16.4%) compared with controls (5.7%). Seventy-one IgAN patients had their renal biopsies graded according to histopathological severity: grades I, II or III. There was no statistical difference in the DR and DQ alleles among the three grades. Seventy-three patients were classified into group A with normal and stable renal function (serum creatinine < or = 150 mumol/liter) and group B with chronic renal failure (serum creatinine > 150 mumol/liter). There was a significant increase in frequency of DQA2 U (DX alpha U) allele in group B (66.9%) compared with group A (26.9%). Also, there was an increased frequency of DQ alpha 2 allele in the group A (40.4%) compared with group B (14.3%). Out of the 24 patients carrying the DQ alpha 2 allele, 17 were DQA2 U allele-negative and they all had normal renal function, suggesting that DQA2 U allele is associated with a poor prognostic factor in IgAN. The study shows that DQ alleles are probably the important genetic loci or are close markers for the disease susceptibility and prognostic index for IgAN in Chinese people.