Tourette syndrome and genetics
Tourette syndrome is a chronic neurological disorder characterized by the presence of both motor and vocal tics, which are rapid and involuntary movements or sounds. It typically begins before the age of eighteen and must persist for over a year for a diagnosis to be made. The exact etiology of Tourette syndrome is complex and not fully understood, but it is believed to involve both genetic and environmental factors. The SLITRK1 gene, located on chromosome 13, has been associated with some cases, though mutations in this gene are not found in the majority of individuals with the syndrome.
Genetic predisposition is evident, as Tourette syndrome appears to cluster in families; however, isolated cases without family history also occur. Symptoms can vary significantly in severity and may improve with age or during periods of concentration, though stress often exacerbates them. Treatment options include medications to help manage tics and behavioral therapies, but there is no known prevention for the disorder. Understanding the interplay between genetics and environmental influences may provide insights into more effective treatments and support for those affected by Tourette syndrome.
Tourette syndrome and genetics
ALSO KNOWN AS: Tourette’s syndrome
DEFINITION Tourette syndrome is a chronic, neurological disorder that is a member of a larger group of primary tic disorders. It is characterized by motor and vocal tics. Both motor and vocal tics must be present, though not necessarily at the same time. Tics must be present for more than one year, and its onset must be prior to age eighteen. Tics are rapid, involuntary movements or sounds that occur repeatedly.
Risk Factors
Patients should tell their doctors if they have any of the risk factors, which include a family history of Tourette syndrome, other tic disorders, or obsessive-compulsive disorder. Males are three to four times more likely to be affected. Another risk factor is strep infection (may be a risk in some children).
There are many secondary causes of tics, including hereditary disorders, carbon monoxide poisoning, traumatic brain injury, cerebral infections, medications, and illegal drugs.
Etiology and Genetics
The causes of Tourette syndrome are complex and poorly understood, but it is likely that both genetic and environmental factors are involved. The characteristic tics expressed by individuals with Tourette syndrome probably result from changes in levels or activities of any of several different neurotransmitters, chemicals produced in the brain that help produce and control voluntary motion.
The only specific gene reported to be associated with cases of Tourette syndrome is the SLITRK1 gene, found on the long arm of chromosome 13 at position 13q31.1. The normal protein product of this gene is a member of a family of proteins that orchestrate the growth and development of neurons. Specifically, the SLITRK1 protein may be important for the development of the long extensions of nerve cells, called dendrites and axons, which facilitate chemical communication between cells. It is unclear how mutations in this gene might lead to the behavioral features characteristic of the syndrome. The majority of people with Tourette syndrome do not have mutations in the SLITRK1 gene, so it is clear that a variety of genetic and environmental factors must be involved as opposed to changes in this one single gene. Some cases of the syndrome do appear to cluster in families. A study found the rate was 53 percent for monozygotic twins and 8 percent for dizygotic twins. However, there are also many examples of isolated diagnoses in which there is no previous family history. As a result, it is not possible to reliably predict inheritance patterns.
Symptoms
Symptoms range from mild to severe, but most cases are mild. They can occur suddenly, and the length of time they last can vary. Tics may temporarily decrease with concentration or distraction. During times of stress, they may occur more often.
Tics are divided into motor and vocal, and then subdivided into simple and complex. Common examples of motor tics include simple tics, such as eye blinking, facial grimacing, head jerking, and arm or leg thrusting; and complex tics, such as jumping, smelling, touching things or other people, and twirling around. Common examples of vocal tics include simple tics, such as throat clearing, coughing, sniffing, grunting, yelping, and barking; and complex tics, such as saying words or phrases that do not make sense in a given situation and saying obscene or socially unacceptable words (called coprolalia).
Many people with Tourette syndrome also have one or more of the following problems: obsessions, compulsions, and ritualistic behaviors; attention deficit disorder, with or without hyperactivity (ADD or ADHD); learning disabilities; difficulties with impulse control; and sleep disorders.
While tics may occur throughout life, older teens may find that symptoms improve.
Screening and Diagnosis
The doctor will ask about a patient’s symptoms and medical history and will perform a physical exam. Tourette syndrome is diagnosed by observing the symptoms and reviewing when they began and how they progressed. There are no blood or neurological tests to diagnose Tourette syndrome. Some doctors may order a magnetic resonance imaging (MRI) scan, a computed tomography (CT) scan, an electroencephalogram (EEG), or blood tests to rule out other disorders.
Treatment and Therapy
Most people with Tourette syndrome do not need medical treatment. If patients have a tic that disrupts daily activities, there are treatments. The most common is medication. No single treatment is helpful for all people with Tourette syndrome. Treatment may not completely eliminate symptoms.
Several medications can help control tics, including clonidine (Catapres), pimozide (Orap), risperidone (Risperdal), and haloperidol (Haldol), as well as newer antipsychotic medications, such as aripiperazole (Abilify) and ziprasidone (Geodon). Obsessive-compulsive symptoms may be treated with fluoxetine (Prozac), clomipramine (Anafranil), sertraline (Zoloft), or other similar medications. Symptoms of ADHD may be treated with stimulants, such as methylphenidate (Ritalin), pemoline (Cylert), dextroamphetamine sulfate (Dexedrine), or tricyclic antidepressants.
Other forms of treatment include behavior therapy, which can help people with Tourette syndrome learn to substitute their tics with alternative movements or sounds that are more acceptable. Cognitive behavioral therapy can help reduce obsessive-compulsive symptoms. Relaxation, biofeedback, and exercise can reduce the stress that often makes symptoms worse.
Psychotherapy can help people with Tourette syndrome and their families cope with the disorder. In tic disorders associated with pediatric autoimmune neuropsychiatric disorders associated with streptococcal (PANDAS), intravenous immunoglobulin therapy has been used with some success in a small number of patients, but this therapy is still considered experimental.
Prevention and Outcomes
There is currently no known way to prevent Tourette syndrome.
Bibliography
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