Familiality of Co-existing ADHD and Tic Disorders: Evidence from a Large Sibling Study

Area of Science:

• Neurodevelopmental disorders
• Genetics of psychiatric disorders
• Child and adolescent psychiatry

Background:

• Attention-deficit/hyperactivity disorder (ADHD) and tic disorder (TD) frequently co-occur.
• Familial aggregation patterns of combined ADHD and TD are not well understood.
• Previous studies on the familial transmission of ADHD+TD are limited and inconclusive.

Purpose of the Study:

• To investigate for the first time in a large ADHD sample if ADHD with co-existing TD (ADHD+TD) increases the risk of ADHD+TD in siblings.
• To determine if this familial risk is independent of general psychopathological vulnerability.
• To examine the familial risk for TD in siblings of individuals with ADHD+TD.

Main Methods:

• Utilized data from the International Multicenter ADHD Genetics (IMAGE) study, including 2815 individuals.
• Assessed psychopathological symptoms using the Strength and Difficulties Questionnaire (SDQ) and Conners' Rating Scales (CRS).
• Employed logistic regression (GENMOD procedure) to analyze sibling risk for ADHD, TD, and ADHD+TD based on index patient diagnoses.

Main Results:

• ADHD+TD in index patients significantly increased the risk for both ADHD+TD and TD in their full siblings.
• The observed familial risk for ADHD+TD and TD was not associated with general psychopathological symptoms in siblings.
• Tic disorder (TD) segregation appeared to be the primary factor driving familial risk, irrespective of ADHD.

Conclusions:

• The co-existence of ADHD and TD shows familial aggregation, suggesting shared genetic or environmental factors.
• Tic disorder (TD) appears to be a key factor in the familial transmission of these conditions.
• Clinical guidelines should emphasize thorough ADHD assessment in individuals diagnosed with TD due to their close relationship and shared familial risk.