What is the connection between red hair and Tourette syndrome?

Tourette syndrome is a chronic, idiopathic, childhood onset neuropsychiatric disorder with both motor and vocal tics. Tourette syndrome occurs worldwide and the clinical features are similar irrespective of the country of origin, with genetic causes suspected, but to date not proven. A link between red hair colour and Tourette syndrome has been hypothesised as a result of an observation that red hair is over represented in this condition. A causal association between red hair and melanocortin-1 receptor has been shown, and is the only gene that is known to explain physiological variation in human pigmentation. Melanocortins are believed to be involved in many disease states including pigmentary disorders, adrenal disorders, obesity, anorexia, prolonged and neuropathic pain, and inflammatory response. The mode of inheritance for Tourette syndrome is thought to be autosomal recessive, same as for red hair with both aggregating in families. To explore the hypothesis, 168 postal questionnaires sent to Tourette syndrome patients on the registry of the 'Tourette Syndrome Association of Australia', were analysed. In this study 22, 13% (95% CI 8.9-19.4) of the Tourette syndrome population had red hair. Data from Australian studies suggests, the normal population with red hair is 2-6%. The proportions of red haired individuals in this study were significantly higher than five of the eight population control groups. Fifty five percent of the Tourette syndrome patients had relatives with red hair. Of these 30% were first degree and 46% were second degree relatives, with a further 24% of more distant relatives. Many Tourette syndrome patients had multiple red haired relatives, since 90 patients yielded a total of 181 relatives with red hair. If this hypothesis is correct the MCIR gene, through a neurological effect, or a gene for Tourette syndrome, located on chromosome 16 in the vicinity of MC1R, could be on the causal pathway. As these figures demonstrate, the hypothesis that there is an association between red hair and Tourette syndrome needs further evaluation.