Meta-analysis of association between obsessive-compulsive disorder and the 3' region of neuronal glutamate transporter gene SLC1A1

The neuronal glutamate transporter gene SLC1A1 is a candidate gene for obsessive-compulsive disorder (OCD) based on linkage studies and convergent evidence implicating glutamate in OCD etiology. The 3' end of SLC1A1 is the only genomic region with consistently demonstrated OCD association, especially when analyzing male-only probands. However, specific allele associations have not been consistently replicated, and recent OCD genome-wide association and meta-analysis studies have not incorporated all previously associated SLC1A1 SNPs. To clarify the nature of association between SLC1A1 and OCD, pooled analysis was performed on all available relevant raw study data, comprising a final sample of 815 trios, 306 cases and 634 controls. This revealed weak association between OCD and one of nine tested SLC1A1 polymorphisms (rs301443; uncorrected P = 0.046; non-significant corrected P). Secondary analyses of male-affecteds only (N = 358 trios and 133 cases) demonstrated modest association between OCD and a different SNP (rs12682807; uncorrected P = 0.012; non-significant corrected P). Findings of this meta-analysis are consistent with the trend of previous candidate gene studies in psychiatry and do not clarify the putative role of SLC1A1 in OCD pathophysiology. Nonetheless, it may be important to further examine the potential associations demonstrated in this amalgamated sample, especially since the SNPs with modest associations were not included in the more highly powered recent GWAS or in a past meta-analysis including five SLC1A1 polymorphisms. This study underscores the need for much larger sample sizes in future genetic association studies and suggests that next-generation sequencing may be beneficial in examining the potential role of rare variants in OCD.

Is obsessive-compulsive disorder an autoimmune disease?

OBSESSIVE-COMPULSIVE DISORDER (OCD) IS A COMMON and debilitating neuropsychiatric disorder. Although it is widely believed to have a genetic basis, no specific genetic factors have been conclusively identified as yet, leading researchers to look for environmental risk factors that may interact with an underlying genetic susceptibility in affected individuals. Recently, there has been increasing interest in a possible link between streptococcal infections and the development of OCD and tic disorders in children. It has been suggested that OCD in some susceptible individuals may be caused by an autoimmune response to streptococcal infections, that is, a similar biological mechanism to that associated with Sydenham's chorea. The term "pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections" (PANDAS) has been used to describe a subset of children with abrupt onset or exacerbations of OCD or tics, or both, following streptococcal infections. Affected children have relatively early symptom onset, characteristic comorbid symptoms and subtle neurological dysfunction. Neuroimaging studies reveal increased basal ganglia volumes, and the proposed cause involves the cross-reaction of streptococcal antibodies with basal ganglia tissue. Vulnerability to developing PANDAS probably involves genetic factors, and elevated levels of D8/17 antibodies may represent a marker of susceptibility to PANDAS. Prophylactic antibiotic treatments have thus far not been shown to be helpful in preventing symptom exacerbations. Intravenous immunoglobulin therapy may be an effective treatment in selected individuals. Further understanding of the role of streptococcal infections in childhood-onset OCD will be important in determining alternative and effective strategies for treatment, early identification and prevention of this common and debilitating psychiatric disorder.

Velo-cardio-facial syndrome: Implications of microdeletion 22q11 for schizophrenia and mood disorders

Velo-cardio-facial syndrome (VCFS) is a congenital malformation syndrome with variable phenotypic features that has been associated with chromosomal microdeletion 22q11.2. Psychiatric disorders have been reported to be highly prevalent in individuals with this syndrome, and the objective of this study was to assess the nature and extent of psychopathology among individuals with VCFS. We studied 20 children and adolescents with 22q11 deletions determined by fluorescence in situ hybridization (FISH). Control subjects were 11 nondeleted siblings who were the closest age match to the affected subjects. Both affected and control subjects were assessed using two standardized psychiatric research instruments. The results of this study confirmed the high rate of psychiatric disorders among VCFS subjects (60% of our subjects). Of the specific types of disorders, only mood disorders were significantly more common among VCFS subjects compared to sibling controls, with eight VCFS subjects having mood disorders compared with none of the control subjects (P<0.02). Three affected subjects had schizotypal traits comorbid with a mood disorder. In addition, disruptive behavior disorders were frequently diagnosed among VCFS subjects. Using a dimensional measure of psychopathology, significant differences between VCFS subjects and sibling controls were found on three scales: ADHD (P<0.02), separation anxiety (P<0.02), and depression (P<0.01). VCFS subjects were achieving significantly less well academically and requiring significantly more special educational assistance than sibling controls. Follow-up data were available on two subjects, both of whom had been diagnosed with schizophrenia. Further research on psychopathology in VCFS may provide a model of how a specific genetic defect can lead to the development of psychiatric disorders.

Fatigue and heat production in repeated contractions of mouse skeletal muscle

1. This study tested the hypothesis that moderate fatigue of skeletal muscle arises from a mismatch between energy demand and energy supply. Fatigue was defined as the decline in isometric force. Energy supply and demand were assessed from measurements of muscle heat production. 2. Experiments were performed in vitro (21 degrees C) with bundles of muscle fibres from mouse fast-twitch extensor digitorum longus muscle and slow-twitch soleus muscle. Fibre bundles were fatigued using a series of thirty isometric tetani. Cycle duration (time between successive tetani) was 5 s. The amount of fatigue that occurred during a series of tetani was varied by varying contraction duty cycle (tetanus duration/cycle duration) by varying tetanus duration. 3. Peak isometric force and total heat production in each cycle were measured. For each cycle, the amounts of initial heat (H(i)) and recovery heat (Hr) produced were calculated and used as indices of energy use and supply, respectively. H(i) and Hr were used to estimate the net initial chemical breakdown (in energy units) in each cycle (H(i,net)). 4. The magnitude of H(i,net) was greatest in the early stages of the contraction protocol when Hr was still increasing towards a steady value. The magnitude of decline in force between successive tetani was proportional to H(i,net) for both muscles. 5. The results are consistent with the idea that the development of moderate levels of fatigue at the start of a series of contractions is due to the rate of energy supply being inadequate to match the rate of energy use.

Xanthine oxidase does not mediate the antiproliferative effects of interferon-gamma in human umbilical vein endothelial cells

Interferon-gamma (IFN-gamma) has potent antiproliferative effects on the endothelium, although the specific mechanisms responsible for this effect are not clear. We tested the hypothesis that suppression of endothelial cell proliferation by IFN-gamma is mediated by an increase in xanthine oxidase-derived O2-.. Human umbilical vein endothelial cells (HUVEC) were exposed to recombinant human IFN-gamma. We found that [3H]thymidine uptake decreased (p < 0.05) with increasing doses of IFN-gamma. Treatment of HUVEC with the xanthine oxidase inhibitor allopurinol or the O2-. scavenger superoxide dismutase had no effect (p > 0.05) on [3H]thymidine uptake of IFN-gamma-treated cells. In parallel, IFN-gamma decreased (p < 0.05) HUVEC cell counts, while allopurinol again had no effect (p > 0.05) on cell counts of IFN-gamma-treated or control HUVEC. In addition, xanthine oxidase activity of HUVEC did not (p > 0.05) increase following treatment with IFN-gamma. We conclude that IFN-gamma suppresses HUVEC proliferation by a mechanism independent of O2-. production by xanthine oxidase.