A recent genetic study proposed complement component 4 (C4) as a possible candidate gene in the MHC region of chromosome 6, for the pathogenesis of schizophrenia.92 C4, located near the strongest peak of association with schizophrenia at the MHC region,92 has two isotypes of the gene, C4A and C4B, in humans. This evidence concerns the gene C4B and schizophrenia.