Epidemiology and Genetics a Family studies indicate a genetic predisposition a The class Ii major histocompatibility complex allele HLA-DR4 (DRB1* 0401) and related alleles are known to be major genetic risk factors for raEpidemiology and Genetics  Family studies indicate a genetic predisposition.  The class II major histocompatibility complex allele HLA-DR4 (DRß1*0401) and related alleles are known to be major genetic risk factors for RA