Objective: Tourette syndrome (TS) and attention-deficit hyperactivity disorder (ADHD) are frequently seen in combination, though the cause of comorbidity is uncertain. Low birth weight is a known risk factor for ADHD. The objective of the study was to assess the association between pre- and perinatal morbidity and the comorbid diagnosis of ADHD in children with TS.
Method: A nested case-control study of children evaluated for TS at a subspecialty clinic was performed. Cases were defined as children with TS and ADHD; controls had TS without ADHD. Exposure to pre- and perinatal morbidity was assessed using demographic information booklets completed by parents before the diagnostic interview.
Results: Three hundred fifty-three children were included, 181 cases and 172 controls. Children with TS and ADHD had a greater odds of exposure to low birth weight status, prematurity, breathing problems, and maternal smoking compared with children with TS only. A multivariable logistic regression model found adjusted odds ratios for the comorbid diagnosis of TS and ADHD of 2.74 (95% CI 1.03–7.29, p = .04) in children born low birth weight, and of 2.43 (95% CI 1.23–4.82, p = .01) for children exposed to maternal smoking.
Conclusion: In children with TS, there is a greater odds of comorbid ADHD in children born with low birth weight or with exposure to maternal smoking. The commonality of risk factors for ADHD only and tic-related ADHD supports a common underlying neurobiology. Women with fetuses at risk for TS should avoid smoking and preventable causes of low birth weight to minimize the risk of comorbid ADHD.
From the *Department of Clinical Neurosciences and Pediatrics, University of Calgary, Calgary, Alberta, Canada; †Department of Psychiatry, University of Toronto, Toronto, Canada; ‡Division of Neurology, University of Toronto, Toronto, Canada; and §Department of Pediatrics, University of Toronto, Toronto, Canada.
Received November 2008; accepted January 2009.
Address for reprints: Tamara Pringsheim, MD, MSc, Alberta Children's Hospital, C4-431, 2888 Shaganappi Trail NW, Calgary AB, T3B 6A8, Canada; e-mail: firstname.lastname@example.org.