Human QKI, a new candidate gene for schizophrenia involved in myelination.

We have previously shown that chromosome 6q25-6q27 includes a susceptibility locus for schizophrenia in a large pedigree from northern Sweden. In this study, we fine-mapped a 10.7 Mb region, included in this locus, using 42 microsatellites or SNP markers. We found a 0.5 Mb haplotype, likely to be inherited identical by decent, within the large family that is shared among the majority of the patients (69%). A gamete competition test of this haplotype in 176 unrelated nuclear families from the same geographical area as the large family showed association to schizophrenia (empirical P-value 0.041). The only gene located in the region, the quaking homolog, KH domain RNA binding (mouse) (QKI), was investigated in human brain autopsies from 55 cases and 55 controls using a high-resolution mRNA expression analysis. Relative mRNA expression levels of two QKI splice variants were clearly downregulated in schizophrenic patients (P-value 0.0004 and 0.03, respectively). The function of QKI has not been studied in humans, but the mouse homolog is involved in neural development and myelination. In conclusion, we present evidence from three unrelated sample-sets that propose the involvement of the QKI gene in schizophrenia. The two family based studies suggest that there may be functional variants of the QKI gene that increase the susceptibility of schizophrenia in northern Sweden, whereas the case-control study suggest that splicing of the gene may be disturbed in schizophrenic patients from other geographical origins. Taken together, we propose QKI as a possible target for functional studies related to the role of myelination in schizophrenia.