A haplotype containing quantitative trait loci for SLC1A1 gene expression and its association with obsessive-compulsive disorder

Abstract

Context: Recent evidence from linkage analyses and follow-up candidate gene studies supports the involvement of SLC1A1, which encodes the neuronal glutamate transporter, in the development of obsessive-compulsive disorder (OCD).

Objectives: To determine the role of genetic variation of SLC1A1 in OCD in a large case-control study and to better understand how SLC1A1 variation affects functionality.

Design: A case-control study.

Setting: Publicly accessible SLC1A1 expression and genotype data.

Patients: Three hundred twenty-five OCD probands and 662 ethnically and sex-matched controls.

Interventions: Probands were assessed with the Structured Clinical Interview for DSM-IV, the Yale-Brown Obsessive Compulsive Scale, and the Saving Inventory-Revised. Six single-nucleotide polymorphisms (SNPs) were genotyped. Multiple testing corrections for single-marker and haplotype analyses were performed by permutation.

Results: Gene expression of SLC1A1 is heritable in lymphoblastoid cell lines. We identified 3 SNPs in or near SLC1A1 that correlated with gene expression levels, 1 of which had previously been associated with OCD. Two of these SNPs also predicted expression levels in human brain tissue, and 1 SNP was further functional in reporter gene studies. Two haplotypes at 3 SNPs, rs3087879, rs301430, and rs7858819, were significantly associated with OCD after multiple-testing correction and contained 2 SNPs associated with expression levels. In addition, another SNP correlating with SLC1A1 gene expression, rs3933331, was associated with an OCD-hoarding subphenotype as assessed by 2 independent, validated scales.

Conclusions: Our case-control data corroborate previous smaller family-based studies that indicated that SLC1A1 is a susceptibility locus for OCD. The expression and genotype database-mining approach we used provides a potentially useful complementary approach to strengthen future candidate gene studies in neuropsychiatric and other disorders.

Figures

Figure 1

Regression of SLC1A1 expression on single-nucleotide polymorphisms using publicly accessible lymphoblastoid cell line data. Depicted here are 3 cis-acting expression quantitative trait loci that were nominally significant and had the same direction of effect in 2 independent data sets., The single-nucleotide polymorphism rs301430 has previously been shown to be associated with obsessive-compulsive disorder both as a single marker and as part of a haplotype., A, Stranger et al and Spielman et al data, P=.02. B, Stranger et al data, P=.02; Spielman et al data, P=.005. C, Stranger et al data, P=.02; Spielman et al data, P=.01.

Figure 2

Regression of SLC1A1 expression on single-nucleotide polymorphisms in brain tissue. A total of 97 samples of human postmortem dorsolateral prefrontal cortex were genotyped and quantitated for SLC1A1 messenger RNA levels by real-time reverse-transcriptase–polymerase chain reaction. Two of the 3 expression quantitative trait loci single-nucleotide polymorphisms that were analyzed were nominally significant and had the same direction of effect in brain tissue as in lymphoblastoid cell lines (Figure 1). A, nonsignificant. B, P=.02. C, P=.02.

Figure 3

Reporter gene analyses of putative expression quantitative trait loci. The 3 single-nucleotide polymorphisms identified in this study to be associated with SLC1A1 messenger RNA levels were tested in luciferase constructs. Six constructs were transfected 5 times in both human neuroblastoma (SH-SY5Y) and rat pheochromocytoma (PC12) cell lines. Error bars represent standard error of mean. One single-nucleotide polymorphism, rs301430, showed allele-specific differential luciferase expression that was highly significant in neuroblastoma (t8=8.6, P<.001) and in PC12 cells (t8=6.1, P<.001). Note that the T allele–mediated reduction in luciferase expression for rs301430 is in line with the T allele–associated decrease in SLC1A1 messenger RNA levels in lymphoblastoid cell lines and brain tissue (Figure 1 and Figure 2). NS indicates nonsignificant.

Figure 4

Two linear regression analyses of rs3933331 for the hoarding subphenotype, both factor analysis–derived (A) and on the basis of the Saving Inventory–Revised (SIR) score (B), which were nominally significant. A, P=.005. B, P=.009.