Alleles of the alpha1 immunoglobulin gene 3' enhancer control evolution of IgA nephropathy toward renal failure.
BACKGROUND
IgA nephropathy is the most common glomerular disease. Mechanisms leading to its occurrence and controlling the evolution of the disease remain largely unknown. Various genetic factors have been found, mostly implicating immunologically relevant genes (IgH, TCR, human lymphocyte antigen, and complement loci). A regulatory region recently identified downstream, the alpha1 gene of the IgH locus, was a likely candidate for the control of IgA1 production in patients. Alleles of this region, differing by size, sequence, and orientation of the alpha1 hs1,2 transcriptional enhancer, were first identified through Southern blot hybridization.


METHODS
We established a polymerase chain reaction (PCR) method suitable for routine testing that amplifies minisatellites within the alpha1 hs1, 2 enhancer, with variable numbers of tandem repeats (VNTR) defining the two alleles. This assay allowed the typing of 104 patients with IgAN and 83 healthy volunteers. Results from typing of alpha1 hs1,2 alleles were compared with long-term clinical outcome in patients. Enhancer alleles were compared in a luciferase reporter gene assay.


RESULTS
The alpha1 hs1,2 alleles do not constitute a predictive factor for IgA nephropathy, since similar allelic frequencies were observed in healthy individuals and in unrelated European patients. In contrast, among patients, homozygosity for the weakest enhancer allele (AA genotype) was significantly correlated with a milder form of the disease, whereas the allele B was associated with severe evolution. The minisatellite region within the alpha1 hs1,2 enhancer carried potential transcription factor-binding sites, and its duplication increased the transcriptional strength of the alpha1 hs1, 2 allele B over that of allele A.


CONCLUSIONS
Altogether, these alleles may constitute a risk factor for the prognosis of IgA nephropathy.
Aupetit
C
C
Laboratoire d'Immunologie, CNRS EP 118 Faculté de Médecine and Institut Universitaire de France, and Service de Néphrologie, C.H.U. Dupuytren, Limoges; and Service de Néphrologie, C.H.U. Jean Bernard, Poitiers, France.
Drouet
M
M
Pinaud
E
E
Denizot
Y
Y
Aldigier
J C
JC
Bridoux
F
F
Cogné
M
M
D020413:3' Untranslated Regions / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000483:Alleles; D003001:Cloning, Molecular; D004276:DNA, Satellite; D018450:Disease Progression; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation / Q000276:immunology; D017930:Genes, Reporter; D005838:Genotype; D005922:Glomerulonephritis, IGA / Q000235:genetics*; D006801:Humans; D007070:Immunoglobulin A / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D008156:Luciferases / Q000235:genetics; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction / Q000379:methods; D011379:Prognosis; D051437:Renal Insufficiency / Q000235:genetics*
D020413:3' Untranslated Regions; D004276:DNA, Satellite; D007070:Immunoglobulin A; D007143:Immunoglobulin Heavy Chains; D008156:Luciferases