Tryptophan hydroxylase type 2 variants modulate severity and outcome of addictive behaviors in Parkinson's disease

Roberto Cilia, Roberta Benfante, Rosanna Asselta, Laura Marabini, Emanuele Cereda, Chiara Siri, Gianni Pezzoli, Stefano Goldwurm, Diego Fornasari

Research output: Contribution to journalArticlepeer-review


Background: Impulse control disorders and compulsive medication intake may occur in a minority of patients with Parkinson's disease (PD). We hypothesize that genetic polymorphisms associated with addiction in the general population may increase the risk for addictive behaviors also in PD. Methods: Sixteen polymorphisms in candidate genes belonging to five neurotransmitter systems (dopaminergic, catecholaminergic, serotonergic, glutamatergic, opioidergic) and the BDNF were screened in 154 PD patients with addictive behaviors and 288 PD control subjects. Multivariate analysis investigated clinical and genetic predictors of outcome (remission vs. persistence/relapse) after 1 year and at the last follow-up (5.1 ± 2.5 years). Results: Addictive behaviors were associated with tryptophan hydroxylase type 2 (TPH2) and dopamine transporter gene variants. A subsequent analysis within the group of cases showed a robust association between TPH2 genotype and the severity of addictive behaviors, which survived Bonferroni correction for multiple testing. At multivariate analysis, TPH2 genotype resulted the strongest predictor of no remission at the last follow-up (OR[95%CI], 7.4[3.27-16.78] and 13.2[3.89-44.98] in heterozygous and homozygous carriers, respectively, p <0.001). The extent of medication dose reduction was not a predictor. TPH2 haplotype analysis confirmed the association with more severe symptoms and lower remission rates in the short- and the long-term (p <0.005 for all analyses). Conclusion: The serotonergic system is likely to be involved in the pathophysiology of addictive behaviors in PD, modulating the severity of symptoms and the rate of remission at follow-up. If confirmed in larger independent cohorts, TPH2 genotype may become a useful biomarker for the identification of at-risk individuals.

Original languageEnglish
JournalParkinsonism and Related Disorders
Publication statusAccepted/In press - Dec 30 2015


  • Addiction
  • Genetics
  • Impulse control disorders
  • Parkinson disease
  • Serotonin

ASJC Scopus subject areas

  • Geriatrics and Gerontology
  • Clinical Neurology
  • Neurology


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