Tourette’s Syndrome and the Risk of Psychiatric and Neurodevelopmental Disorders in Siblings

Abstract

Tourette’s Syndrome (TS) is a neurodevelopmental disorder that affects up to 1% of the global population. It is typically characterised by the presence of both motor and vocal tics, but encompasses a variety of additional symptoms. This study aims to be the first to explore the likelihoods of specific mental and neurodevelopmental disorders in the siblings of people with TS.

A dataset comprised of 35,295 individuals, of which 21,414 were siblings, born between 1991-2010 and 1977-2013 respectively was compiled. It was populated with data from three national registers: the Finnish Care Register for Health Care (CRHC), the Finnish Digital and Population Data Services Agency (DPDSA), and the Finnish Medical Birth Register (MBR).

A nested case-control design was then used and each sibling case (n=2188) was matched to four controls (n=6963) within the dataset. The included covariates were parity, parental age, parental psychiatric diagnoses, maternal socioeconomic status, and parental immigration. Sibling psychiatric disorders were also taken from registers. A conditional logistic regression using generalised estimating equations (GEEs) was used to create three models from the data: an unadjusted model and two models adjusted for all covariates.

The siblings of people with TS were shown to have a significantly increased incidence of mental and neurodevelopmental disorders, with the likelihood being 1.4 times that of the average for the sibling of a person without TS. Of the investigated disorders, the ones with a significantly increased incidence were mood/affective disorders (adjusted odds ratio (aOR) 1.4, 95% CI 1.2-1.6), anxiety-derived disorders (1.3 aOR, 95% CI 1.1-1.6), autism spectrum disorder (aOR 2.2, 95% CI 1.5-3.2), attention deficit hyperactivity disorder (aOR 1.6, 95% CI 1.2-2.1,), and other neurodevelopmental disorders (aOR 1.4, 95% CI 1.2-1.6 and aOR 1.5, 95% CI 1.3-1.7).

The clustering of psychiatric disorders among siblings could imply a shared genetic or environmental factor in these disorders, setting up a groundwork for future genetic and comparative studies.