Phenylalanine-to-tyrosine ratio in assessment of tetrahydrobiopterin responsiveness in hyperphenylalaninemia
Following an original research paper by Zerjav Tansek et al., published in 2012 (doi: 10.1016/j.ymgme.2012.07.010), we performed a post-hoc analysis of the data on the role of phenylalanine-to-tyrosine ratio in the assessment of the tetrahydrobiopterine (BH4) responsiveness in patients with hyperphenylalaninemia. At the time of the original submission, phenylalanine-to-tyrosine ratios were not reported or analyzed. Due to the gaining role of this ratio, we share with the scientific community the data on tyrosine and phenylalanine-to-tyrosine ratios in assessment of BH4-responsiveness. Methods All patients received 2 g/kg body weight of protein for the time of the assessment (four days prior and one day after BH4-loading). Blood samples were taken four (-96h), three (-72h), two (-48h), one (-24h) and 16h prior to BH4 administration and 8 and 24h after BH4. Blood samples were smeared on to a special filter paper and analyzed by tandem mass spectrometry. BH4-responders were defined when the reduction of blood phenylalanine was ≥30% 24h after BH4 administration. The data was obtained from the patients' Electronic Health Records at the University Children's Hospital, University Medical Centre. Findings Phenylalanine-to-tyrosine ratio can be used as a parameter for predicting tetrahydrobiopterine response in patients with hyperphenylalaninemia.