High Resolution Haplotype Analyses of Classical HLA Genes in Families With Multiple Sclerosis Highlights the Role of HLA-DP Alleles in Disease Susceptibility.

Multiple sclerosis (MS) susceptibility shows strong genetic associations with HLA alleles and haplotypes. We genotyped 11 HLA genes in 477 non-Hispanic European MS patients and their 954 unaffected parents using a validated next-generation sequencing (NGS) methodology. HLA haplotypes were assigned unequivocally by tracing HLA allele transmissions. We explored HLA haplotype/allele associations with MS using the genotypic transmission disequilibrium test (gTDT) and multiallelic TDT (mTDT). We also conducted a case-control (CC) study with all patients and 2029 healthy unrelated ethnically matched controls. We performed separate analyses of 54 extended multi-case families by reviewing transmission of haplotype blocks. The haplotype fragment including was significantly associated with predisposition (gTDT: < 2.20e-16; mTDT: =1.61e-07; CC: < 2.22e-16) as reported previously. A second risk allele, (gTDT: = 3.69e-03; mTDT: = 2.99e-03; CC: = 1.00e-02), independent from the haplotype bearing was newly identified. The allele showed significant protection (gTDT: = 8.68e-06; mTDT: = 4.50e-03; CC: = 1.96e-06). Two alleles, (gTDT: = 2.86e-03; mTDT: = 5.56e-02; CC: = 4.08e-05) and (gTDT: = 1.17e-02; mTDT: = 1.16e-02; CC: = 1.21e-02), defined at two-field level also showed protective effects. The HLA class I block, (gTDT: = 5.86e-03; mTDT: = 3.65e-02; CC: = 9.69e-03) and the alleles (gTDT: = 6.28e-04; mTDT: = 2.15e-03; CC: = 1.47e-02) and (gTDT: = 3.20e-03; mTDT: = 6.14e-03; CC: = 1.70e-02) showed moderately protective effects independently from each other and from the class II associated factors. By comparing statistical significance of 11 HLA loci and 19 haplotype segments with both untruncated and two-field allele names, we precisely mapped MS candidate alleles/haplotypes while eliminating false signals resulting from 'hitchhiking' alleles. We assessed genetic burden for the HLA allele/haplotype identified in this study. This family-based study including the highest-resolution of HLA alleles proved to be powerful and efficient for precise identification of HLA genotypes associated with both, susceptibility and protection to development of MS.