Regional mRNA expression of a second tryptophan hydroxylase isoform in the human brain

Tryptophan hydroxylase (TPH) as rate limiting enzyme in the biosynthesis of serotonin plays a major role as candidate gene in several psychiatric disorders. Recently a second TPH isoform (TPH2) was identified in mice which was exclusively expressed in the brain. The aim of the present study was to investigate whether the mRNA of the human homologue of this new TPH2 isoform is expressed in the human brain but not in peripheral tissues. The study was performed with postmortem specimen obtained from control subjects, drug abusers and suicide victims. TPH2 mRNA levels were determined by quantitative real time RT-PCR. TPH2 mRNA was exclusively present in the brain but not in peripheral tissues. Additionally there seems to be interindividual differences in the TPH2 mRNA expression. Our finding opens up new research strategies for the analysis of the repeatedly observed disturbances in the serotonergic system in patients suffering from several psychiatric disorders.