Evidence of linkage between susceptibility to multiple sclerosis and HLA-class II loci in Italian multiplex families.

To verify whether multiallelic polymorphisms belonging to HLA class II genes are linked to multiple sclerosis (MS) in the Italian population, we studied 28 multiplex MS families originating from different areas of Italy. Allelic characterization was carried out by analysis of RFLPs and oligonucleotide typing. Evidence supporting the existence of linkage between MS susceptibility and the HLA class II loci DRB1, DQA1 and DQB1 was provided using two non-parametric tests, affected sib-pair analysis, and affected-pedigree-member (APM) analysis. The APM analysis also suggested the existence of genetic heterogeneity for the HLA class II loci and MS susceptibility in our series. Linkage disequilibrium between MS susceptibility and the haplotype DRB1*1501,DQA1*0102,DQB1*0602 was demonstrated by applying the transmission linkage disequilibrium test to our families. Finally, lod score analysis suggests that in our Italian families, MS susceptibility is conferred by HLA class II alleles according to a low-penetrance autosomal recessive mode of inheritance.