Prenatal maternal smoking a risk factor for severity of Tourette's syndrome

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Maternal smoking during pregnancy appears to be a strong risk factor for increased symptoms severity in subjects with Tourette's syndrome, and for comorbid obsessive-compulsive disorder (OCD).

Tourette's syndrome is believed be to associated with multiple genetic and environmental factors, Dr. Carol A. Mathews and her associates note. While few studies have examined the role of environmental factors, there are suggestions that perinatal incidents and the mother's prenatal habits may affect the occurrence of the disorder, its severity, or the risk of comorbidity.

Dr. Mathews, from the University of California in San Francisco, and her team hypothesized that transient fetal hypoxia could increase the predisposition to developing Tourette's syndrome in those with a genetic vulnerability.

To test this theory, psychiatrists in the research team evaluated members of three cohorts of persons with the syndrome, which included 53 individuals from Costa Rica, 99 individuals of Ashkenazi Jewish descent, and 28 individuals involved in an affected sibling pair study. The ages of the 180 subjects ranged from 3 to 59 years, but 60% were below age 14 when they were interviewed.

The investigators report in the American Journal of Psychiatry for June that the mean tic severity score was 38.6 out of a possible 50, and the mean global severity score was 61 out of a possible 100.

The presence of OCD and comorbid self-injurious behavior was strongly associated with tic severity. Comorbid attention deficit/hyperactivity disorder (ADHD) was also associated with tics, but the association was not as strong as the other two disorders.

More than half of the subjects reported at least one adverse perinatal event, but these were generally similar to that in the general population. Parental factors and perinatal events did not seem to affect risk.

However, after adjusting for subject group, gender, and family history, maternal smoking was significantly associated with total tick and phonic tic severity. In fact, statistical modeling showed that maternal smoking accounted for 42% of the variance in tic severity.

Maternal smoking was also associated with an 8-fold increased risk of comorbid OCD.

The researchers suggest that the association between smoking and tic severity and OCD was evidence that chronic fetal hypoxia increased the risk. However, they cannot rule out the possibility that maternal smoking is an indicator for an associated variable that has yet to be uncovered, such as socioeconomic status or parental ADHD.