A systematic appraisal of the MHC gene variation associated with either autism or schizophrenia

We systematically assessed polymorphic variants within the MHC region reported in the literature and tentatively establish extended haplotypes associated with either schizophrenia or autism risk. We used the key search “(HLA OR 'major histocompatibility complex') AND (autism OR schizophrenia)”. Outcome measures were a) allele counts b) Odds Ratios of individual variants c) strength of linkage-disequilibrium among variants Data collection, quality and strength of evidence rating were assessed according to Cochrane recommendations. We showed that most of the association signals within MHC could point to complement component 4 null allele C4BQ0-bearing haplotypes, which are protective toward schizophrenia and risky for autism.