Is Tic-Related OCD a Distinct Subtype with Stronger Genetic Links?

What you need to know

• Obsessive-compulsive disorder (OCD) that occurs with tic disorders shows stronger familial patterns than OCD without tics.
• People with tic-related OCD tend to develop symptoms earlier and have higher rates of ADHD and autism.
• The stronger familial link in tic-related OCD is not just due to tics being highly heritable themselves.

Background on OCD and tic disorders

Obsessive-compulsive disorder (OCD) is a condition characterized by recurring, intrusive thoughts (obsessions) and repetitive behaviors or mental acts (compulsions). Tic disorders involve sudden, rapid movements or vocalizations that occur repeatedly. When OCD occurs together with tics, it is referred to as tic-related OCD.

Some researchers have proposed that tic-related OCD may be a distinct subtype of OCD. This study aimed to investigate whether tic-related OCD runs more strongly in families compared to OCD without tics, which could support it being a separate subtype.

What the study did

The researchers used Swedish national registers to identify over 4 million people born between 1967-2007. Within this group, they found:

• 1,257 people with tic-related OCD
• 20,975 people with OCD but no tics
• Over 4 million people without OCD (for comparison)

They then looked at rates of OCD diagnosis in the relatives of these individuals, including twins, siblings, half-siblings, and cousins.

Key findings

Stronger familial patterns in tic-related OCD

The study found that OCD runs in families regardless of whether tics are present. However, the familial link was much stronger for tic-related OCD:

• Full siblings of someone with tic-related OCD were about 10 times more likely to have OCD themselves, compared to siblings of people without OCD.
• Full siblings of someone with non-tic-related OCD were about 4 times more likely to have OCD.

This pattern held true across different types of relatives. For example, the risk was about twice as high in twins and maternal half-siblings of people with tic-related OCD compared to non-tic-related OCD.

Earlier onset and different symptoms

People with tic-related OCD tended to:

• Develop OCD symptoms at a younger age (median 15.7 years old vs 23.1 for non-tic OCD)
• Be more likely to be male (71% vs 41%)
• Have higher rates of ADHD (55% vs 17%) and autism (37% vs 13%)

Those with non-tic-related OCD had higher rates of anxiety and mood disorders.

Not just due to tics being heritable

To check if the stronger familial link was simply because tic disorders themselves run in families, the researchers did similar analyses for OCD occurring with ADHD or autism (which are also highly heritable). They did not find the same strong familial patterns for these combinations.

Implications of the findings

These results suggest that tic-related OCD may indeed be a distinct subtype of OCD with a stronger genetic component. This could have several implications:

1. For families: If someone has OCD with tics, their close relatives may be at higher risk of developing OCD compared to families where OCD occurs without tics.

2. For diagnosis and treatment: Recognizing tic-related OCD as a potentially distinct subtype could help in earlier identification and tailored treatment approaches.

3. For research: Studying the genetics of tic-related OCD specifically may be more fruitful in uncovering OCD risk genes than looking at all OCD cases together.

Conclusions

• Tic-related OCD shows much stronger familial patterns than OCD without tics.
• This suggests tic-related OCD may be a genetically distinct subtype of OCD.
• Further research focused on tic-related OCD could help uncover genes that contribute to OCD risk.

While these findings are important for advancing our understanding of OCD, it’s crucial to remember that having a family history of tic-related OCD doesn’t mean someone will definitely develop the condition. Many factors, including environment, contribute to the development of OCD.