HLA DQA1-DQB1-TAP2 haplotypes in IDDM families: no evidence for an additional contribution to disease risk by the TAP2 locus.
The TAP2 gene, located in the HLA class II region, encodes a subunit of a transporter involved in the endogenous antigen-processing pathway, and has been suggested to contribute to the genetic risk for insulin-dependent diabetes (IDDM). In order to determine whether the TAP2 locus modulates the risk conferred by HLA DQ loci, HLA DQA1-DQB1-TAP2 haplotypes were analysed in 48 IDDM probands, their first degree relatives, and in 62 normal control subjects. A decreased frequency of the TAP2B allele was confirmed in this IDDM cohort (12 vs 28% in control subjects, pc < 0.05). Analysis of 73 informative meiotic events in IDDM and control families demonstrated a recombination fraction between HLA DQB1 and TAP2 loci of 0.041 (Log of the odds score = 16.5; p < 10(-8)) indicating strong linkage between these loci. Family haplotype analysis demonstrated linkage disequilibrium between TAP2 and HLA DQA1-DQB1, and showed that the reduced frequency of TAP2B was associated with its absence on the IDDM susceptible DQA1*0301-DQB1*0302 haplotype, its low frequency on DQA1*0501-DQB1*0201, and the association of TAP2B with DQA1*0101-DQB1*0501 haplotypes which were less frequent in IDDM patients. Comparison of transmitted with non-transmitted haplotypes in IDDM families showed a slight but not significant decrease in TAP2B allele frequency on transmitted (3 of 37) vs non-transmitted (2 of 9) HLA DQA1*0501-DQB1*0201 haplotypes. No other differences were observed. Twenty-four unrelated DQA1*0501-DQB1*0201 haplotypes from non-diabetic families had a TAP2B allele frequency (4%) similar to that in IDDM haplotypes.(ABSTRACT TRUNCATED AT 250 WORDS)
Esposito
L
L
Department of Laboratory Medicine, Istituto Scientifico San Raffaele, Milan, Italy.
Lampasona
V
V
Bosi
E
E
Poli
F
F
Ferrari
M
M
Bonifacio
E
E
D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology / Q000235:genetics* / Q000276:immunology*; D005190:Family; D005260:Female; D005787:Gene Frequency; D006683:HLA-DQ Antigens / Q000235:genetics*; D059848:HLA-DQ alpha-Chains; D059866:HLA-DQ beta-Chains; D006239:Haplotypes; D006801:Humans; D008285:Major Histocompatibility Complex; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012307:Risk Factors
D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D006683:HLA-DQ Antigens; D059848:HLA-DQ alpha-Chains; D059866:HLA-DQ beta-Chains; C069050:HLA-DQA1 antigen; C069051:HLA-DQB1 antigen; C071692:TAP2 protein, human