Several studies suggest that the X chromosome may contain a gene for schizophrenia. In the present study, we recruited 142 male schizophrenic patients and their biological mothers from all parts of the United Kingdom to detect a genetic association for the SYP/CACNA1F locus in the Xp11 region and the FACL4 locus in the Xq22.3-Xq23 region. The haplotype-based haplotype relative risk (HHRR) analysis showed allelic association for rs2071316 (chi(2) = 6.85, P = 0.009) and rs5905724 (chi(2) = 5.3, P = 0.02 1) at the CACNA1F locus, but not for rs5943414 and rs1324805 at the FACL4 locus and rs3817678 at the SYP locus. The haplotype analysis showed a 2 weak association for the rs3817678-rs2071316-rs5905724 haplotypes (chi(2) = 12.19, df = 4, P = 0.016) but did not show such an association for the rs5943414-rs1324805 baplotypes (chi(2) = 3.96, df = 2, P = 0.138). Because the linkage disequilibrium signal was detected only at the CACNA1F locus, this gene should perhaps be considered as being a candidate for schizophrenia although further work is needed to draw firm conclusions. (c) 2006 Elsevier Inc. All rights reserved.