Estimation of human leukocyte antigen class I and class II high-resolution allele and haplotype frequencies in the Italian population and comparison with other European populations.

The high-resolution (HR) allele and haplotype frequencies of class I and II human leukocyte antigen (HLA) system were determined in the Italian population from a sample of donors recruited in the Italian Bone Marrow Donor Registry (IBMDR). This study analyzed the HLA-A, -B, -C, -DRB1, and -DQB1 loci. Two different samples were used: donors HR typed at least for one allele, usually when selected for donor-recipient matching (respectively: 3596, 7591, 4715, 57345, and 8196), to make a list of the observed alleles and determine the relative frequencies of the alleles in each class of the corresponding antigen; donors HR randomly typed for both the alleles (respectively: 975, 1643, 1569, 22114, and 2087) to estimate the allele and haplotype frequencies, and two loci linkage disequilibrium. The number of alleles showing a frequency >1% on the total number of observed alleles are 18/75 HLA-A, 28/142 -B, 17/57 -C, 23/154 -DRB1, and 13/31 -DQB1. In each locus they account for more than 88% of the total cumulative frequencies. The most frequent alleles are A*02: 01, B*35: 01, C*04:01, DRB1*07:01, DQB1*03:01. The most frequent five-locus haplotype in the 338 donors randomly typed is A*01: 01-C*07:01-B*08: 01-DRB1*03:01-DQB1*02:01. The genetic comparison of the Italian population with 16 European populations shows a south-north gradient.