How Do Genes and Environment Interact to Influence Tic Severity in Tourette Syndrome?

What you need to know

• This study looked at how genes and environmental factors may interact to influence tic severity in people with Tourette syndrome.
• The researchers found that one genetic variant was associated with higher tic severity on its own.
• They also found evidence that another genetic variant may interact with pre- and perinatal factors (events before and around birth) to influence tic severity.
• However, these findings could not be confirmed in a separate group of participants, so more research is needed.

Background on Tourette syndrome

Tourette syndrome is a neurodevelopmental disorder that causes people to make involuntary movements and sounds called tics. Tics usually start in childhood and can range from mild to severe. While we know that both genetic and environmental factors play a role in Tourette syndrome, we still don’t fully understand the specific genes involved or how they may interact with environmental factors to influence tic severity.

What did this study investigate?

This study aimed to look at two main questions:

1. Are any specific genetic variants associated with tic severity in people with Tourette syndrome?

2. Do any genetic variants interact with environmental factors, specifically events before and around birth, to influence tic severity?

To investigate this, the researchers looked at 98 genetic variants that had been previously linked to Tourette syndrome or related disorders in other studies. They examined whether any of these variants were associated with tic severity on their own, and whether any interacted with a measure of pre- and perinatal events to influence tic severity.

Study design and participants

The study included 518 people diagnosed with Tourette syndrome or chronic tic disorder. The researchers collected information on:

• Lifetime worst tic severity, using a standardized rating scale
• Pre- and perinatal events, like complications during pregnancy or birth, using a questionnaire
• Genetic data for the 98 variants of interest

They then used statistical analyses to look for associations between the genetic variants, pre-/perinatal events, and tic severity.

Key findings

Genetic variant associated with tic severity

The researchers found that one genetic variant, called rs7123010, was significantly associated with tic severity on its own. People who had two copies of a particular version of this variant tended to have higher tic severity.

This variant is located in a gene called ME3, which is involved in certain metabolic processes in the body. However, we don’t yet know how it might influence tic severity.

Gene-environment interaction

The study also found evidence for a potential interaction between another genetic variant (rs6539267) and pre-/perinatal events in relation to tic severity.

Specifically, people who had two copies of a particular version of this variant AND experienced a higher number of pre-/perinatal events tended to have higher tic severity. This suggests that the combination of this genetic risk and environmental factors may work together to influence tic severity.

This variant is located in a gene called POLR3B, which is involved in making proteins. Mutations in this gene can cause other neurological conditions, but its potential role in tics is not yet clear.

Limitations and need for further research

While these findings are interesting, it’s important to note that the researchers were not able to confirm these results in a separate group of participants with Tourette syndrome. This means we can’t be certain that these associations are real, and more research is needed to verify them.

There are a few potential reasons why the results couldn’t be confirmed:

1. Tic severity is likely influenced by many genes, each with a small effect. This makes it difficult to reliably detect the influence of single genetic variants.

2. The study may not have had enough participants to detect small genetic effects reliably.

3. The way tic severity was measured differed slightly between the main study group and the replication group, which could have affected the results.

Conclusions

• This study provides some initial evidence that specific genetic variants may influence tic severity in Tourette syndrome, either on their own or in combination with environmental factors.

• The findings highlight the potential importance of considering both genetic and environmental risk factors when studying Tourette syndrome.

• However, more research with larger groups of participants is needed to confirm these results and better understand how genes and environment work together to influence tics.

• In the future, this type of research could help identify people at higher risk for severe tics and potentially lead to more personalized treatment approaches for Tourette syndrome.