HLA-C and myeloid sarcoma: The strongest genetic variants associated with MS are within the major histocompatibility complex (MHC), a genomic region on chromosome 6 involved in adaptive immune responses.1,2 Genome-wide associated studies (GWAS) of common variants (minor allele frequency (MAF) > 5%) have identified 32 independent loci in the MHC and >200 non-MHC variants that contribute to MS risk.3 However, these common variants only account for 20% of MS heritability.4 One emerging theme in genetic studies has been the importance of rare (MAF < 1%) and low-frequency (MAF < 5%) variants in disease heritability.