TPH2 G/T polymorphism is associated with hyperphagia, IQ, and internalizing problems in Prader-Willi syndrome

Background: Prader-Willi syndrome (PWS) is a genetic, neurodevelopmental disorder characterized by intellectual disabilities, growth hormone dysregulation, hyperphagia, increased risks of morbid obesity, compulsive behaviors, and irritability. As aberrant serotonergic functioning is strongly implicated in PWS, we examined associations between the PWS phenotype and polymorphisms in tryptophan hydroxylase 2 (TPH2), the rate-limiting enzyme in the biosynthesis of serotonin in the brain. Methods: Ninety-two individuals with PWS aged 4 to 50 years (M = 21.97) were genotyped for the TPH2 G703-T polymorphism. IQ testing was conducted in offspring, and parents completed questionnaires that tapped their child's compulsivity, hyperphagia, and other behavior problems. Results: As expected, the frequency of G/T or T/T polymorphisms in participants with PWS (39%) was similar to rates found in the general population (38%). Compared to those with a homozygous (G/G) genotype, individuals with a T allele had significantly higher hyperphagic behavior, drive, and severity scores, and they also had a younger age of onset of hyperphagia. Those with a T allele also had higher IQ scores than their counterparts. Females with a T allele had significantly higher internalizing symptoms, primarily anxiety and depression, than all others. Conclusions: TPH2 G/T polymorphisms, and presumed loss of enzyme function, were associated with specific aspects of the PWS phenotype. Aberrant serotonergic functioning is strongly implicated in hyperphagia in PWS, and females with TPH2 T alleles may be at higher risk for affective or mood disorders. Findings hold promise for examining other serotonin-altering genes in PWS, and for future serotonin-altering treatment trials.