Background: Phenylalanine and tyrosine are precursor amino acids required for the synthesis of dopamine, the main\r\nneurotransmitter implicated in the neurobiology of schizophrenia. Inflammation, increasingly implicated in schizophrenia,\r\ncan impair the function of the enzyme Phenylalanine hydroxylase (PAH; which catalyzes the conversion of phenylalanine to\r\ntyrosine) and thus lead to elevated phenylalanine levels and reduced tyrosine levels. This study aimed to compare\r\nphenylalanine, tyrosine, and their ratio (a proxy for PAH function) in a relatively large sample of schizophrenia patients and\r\nhealthy controls.\r\nMethods: We measured non-fasting plasma phenylalanine and tyrosine in 950 schizophrenia patients and 1000 healthy\r\ncontrols. We carried out multivariate analyses to compare log transformed phenylalanine, tyrosine, and phenylalanine:tyrosine\r\nratio between patients and controls.\r\nResults: Compared to controls, schizophrenia patients had higher phenylalanine (p,0.0001) and phenylalanine: tyrosine\r\nratio (p,0.0001) but tyrosine did not differ between the two groups (p = 0.596).\r\nConclusions: Elevated phenylalanine and phenylalanine:tyrosine ratio in the blood of schizophrenia patients have to be\r\nreplicated in longitudinal studies. The results may relate to an abnormal PAH function in schizophrenia that could become a\r\ntarget for novel preventative and interventional approaches.
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