Correlation of the two most frequent HLA haplotypes in the Italian population to the differential regional incidence of Covid-19

Background: Understanding how HLA polymorphisms may affect both susceptibility, course and severity of Covid- 19 infection could help both at the clinical level to identify individuals at higher risk from the disease and at the epidemiological one to explain the differences in the epidemic trend among countries or even within a specific country. Covid-19 disease in Italy showed a peculiar geographical distribution from the northern most affected regions to the southern ones only slightly touched. Methods: In this study we analysed the regional frequencies for the most common Italian haplotypes from the Italian Bone Marrow Donor Registry (HLA-A, -B, -C and -DRB1 at four-digit level). Then we performed Pearson correlation analyses among regional haplotypes estimated frequency in the population and Covid-19 incidence and mortality. Results: In this study we found that the two most frequent HLA haplotypes in the Italian population, HLA-A*:01:01g-B*08:01 g-C*07:01g-DRB1*03:01g and HLA-A*02.01g-B*18.01g-C*07.01g-DRB1*11.04g, had a regional distribution overlapping that of Covid-19 and showed respectively a positive (suggestive of susceptibility) and negative (suggestive of protection) significant correlation with both Covid-19 incidence and mortality. Conclusions: Based on these results, in order to define such HLA haplotypes as a factor effectively associated to the disease susceptibility, the creation of national networks that can collect patients’ samples from all regions for HLA typing should be highly encouraged.