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Children who had a first-degree relative with chronic tic disorder were no more likely to develop tics after exposure to group A Streptococcus (GAS), data from the European Multicenter Tics in Children Study (EMTICS) cohort showed.

Among this high-risk population, there was no statistical evidence of an association of tic onset with any of four different GAS exposure definitions, reported Anette Eleonore Schrag, MD, PhD, of University College London, and co-authors in .

"There has been much debate about whether the bacteria that causes strep throat, group A streptococcus, plays a role in the development of tic disorders, with previous research providing mixed results," Schrag said in a statement.

"Future studies are needed to investigate whether pathogens other than strep, or other factors that affect the immune system, play a specific role in the development of tics," she added.

The etiology of chronic tic disorders is unclear, though it's known that . Over the years, a syndrome known as (pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections) has been diagnosed in some children with tic symptoms that have emerged or worsened abruptly after strep infection.

Previous research from the EMTICS cohort showed that GAS exposure did not make Tourette syndrome or chronic tic disorders worse but was associated with increased symptoms of hyperactivity and impulsiveness.

"From a clinical perspective, as GAS exposure was not found to be associated with tic onset, our study does not support the widespread ongoing clinical practice by many primary care physicians of ordering throat swabs and antibody tests for GAS or treating with antibiotics when a child presents with a new onset of tics," Schrag and co-authors wrote.

"Moreover, as our companion EMTICS study reported no significant association between GAS exposure and tic exacerbations, investigation or recommendation of active management of GAS infection is unlikely to help modify the course of tics," they added.

Some previous studies that have reported an association between GAS exposure and tic onset relied on health insurance data and were not standardized, prospective assessments of an at-risk population, Schrag and colleagues pointed out.

The researchers followed 259 pediatric patients in the EMTICS cohort who did not have tics but who had a parent or sibling diagnosed with a chronic tic disorder. Participants had a mean baseline age of 6.8 years, and 55.6% were girls.

Children were tested for strep infection at baseline and throughout the study by throat swabs and assessments of serum anti-streptolysin O titers (ASOT) and anti-DNAse B (ADB) titers. They were followed for an average of 1.6 years and had medical evaluations every 2 months, alternating between scheduled hospital visits and telephone interviews.

Parents kept a weekly diary and were told to report any possible sign of tics in their child. Tic onset was defined as the occurrence of a sudden, involuntary movement or vocalization on 3 or more days within a 3-week period, which was confirmed on examination.

Over the course of the study, with an average 1 year of follow-up, 61 children (23.6%) developed tics. Comparing the frequency of tic disorders in children who were exposed to GAS and those who were not showed no association between strep and tic development.

This was consistent whether GAS exposure was defined as new versus ongoing or definite versus possible as well as whether exposure was based on ASOT/ADB titer or throat swab results. The findings persisted after adjusting for age, sex, and parents' education level.

Schrag and colleagues also found a strong association between sex and tic onset, with girls having a 60% lower risk of developing tics than boys (HR 0.4, 95% CI 0.2-0.7), similar to previous studies.

A limitation of the study was that participants were enrolled at 16 study centers across Europe, which may have resulted in small inconsistencies in assessments, the researchers acknowledged.

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