Association between the low molecular weight cytosolic acid phosphatase gene ACP1*A and comorbid features of Tourette syndrome

Dopaminergic polymorphisms in Tourette syndrome: association with the DAT gene (SLC6A3)

Tourette syndrome (TS) is a chronic neuropsychiatric disorder characterized by involuntary motor and phonic tics. The pattern of inheritance and associated genetic abnormality has yet to be fully characterized. A dopaminergic abnormality in this disorder is supported by response to specific therapies, nuclear imaging, and postmortem studies. In this protocol, dopaminergic polymorphisms were examined for associations with TS and attention-deficit hyperactivity disorder (ADHD). Polymorphisms investigated included the dopamine transporter (DAT1 DdeI and DAT1 VNTR), dopamine receptor (D4 Upstream Repeat and D4 VNTR), dopamine converting enzyme (dopamine beta-hydroxylase), and the acid phosphatase locus 1 (ACP1) gene. DNA was obtained from 266 TS individuals +/- ADHD and 236 controls that were ethnicity-matched. A significant association, using a genotype-based association analysis, was identified for the TS-total and TS-only versus control groups for the DAT1 DdeI polymorphism (AG vs. AA, P = 0.004 and P = 0.01, respectively). Population structure, estimated by the genotyping of 27 informative SNP markers, identified 3 subgroups. A statistical re-evaluation of the DAT1 DdeI polymorphism following population stratification confirmed the association for the TS-total and TS-only groups, but the degree of significance was reduced (P = 0.017 and P = 0.016, respectively). This study has identified a significant association between the presence of TS and a DAT polymorphism. Since abnormalities of the dopamine transporter have been hypothesized in the pathophysiology of TS, it is possible that this could be a functional allele associated with clinical expression.

Microarray analysis in Tourette syndrome postmortem putamen

Gene expression patterns in the postmortem putamen of patients with Tourette syndrome (TS) were investigated using cDNA microarrays. A cDNA neuroarray comprising 1537 genes known to be related to neurological or neuropsychiatric disorders was used to compare patient samples (n=3) with those from control subjects (n=4). Z test and Z ratio were used to analyze results; seven genes were found to be upregulated according to our definition (P<0.1, two-tailed, for Z test; P<0.05 for Z ratio) and three were found to be downregulated. Validation experiments were performed using reverse transcription polymerase chain reaction (RT-PCR) and semiquantitative Western blot analyses. RT-PCR showed concordance with microarray in seven of nine selected genes. In contrast, Western blot analyses performed with five proteins showed that only two of five had similar trends between protein content and level of gene expression. The authors note the inherent difficulty in applying microarray technology to complex neurological disorders such as the TS and conclude that further investigations are required to understand how altered expression of these genes is related to the pathophysiology of the disorder.

Tics

PURPOSE OF REVIEW

This paper reviews the recent literature concerning Tourette syndrome and related disorders.

RECENT FINDINGS

Tourette syndrome is a common disorder in children and adolescents, with an established association with attention deficit hyperactivity disorder, obsessive compulsive disorder, and a number of other psychiatric disorders. Both autoimmune and genetic mechanisms are implicated in the pathophysiology of the syndrome, while neuroimaging studies have identified abnormalities in the composition of the basal ganglia and frontal lobe white matter, as well as alterations in dopaminergic activity. When necessary, treatment of tics can be successful with neuroleptics and alpha-2-adrenergic agonists. The use of stimulants in children with Tourette syndrome and comorbid attention deficit hyperactivity disorder does not appear to worsen tics.

SUMMARY

As a result of the recent literature, clinicians can feel comfortable treating children with co-morbid attention deficit hyperactivity disorder and Tourette syndrome with stimulant medications. It has also been established that transient tics are very common in children, and for the most part, non-disabling. In those children with persistent tics, behavioural disorders are associated which may impair success in school and psychosocial functioning. Clinicians have a number of therapeutic options, with recent double-blinded randomized trials of clonidine, risperidone, and desipramine showing benefit. Scientists continue to search for the cause of Tourette syndrome.