Man made disease: clinical manifestations of low phenylalanine levels in an inadequately treated phenylketonuria patient and mouse study

Cyclodextrin-Assisted Surface-Enhanced Photochromic Phenomena of Tungsten(VI) Oxide Nanoparticles for Label-Free Colorimetric Detection of Phenylalanine

Herein are presented the results of experiments designed to evaluate the effectiveness of host-guest interactions in improving the sensitivity of colorimetric detection based on surface-enhanced photochromic phenomena of tungsten(VI) oxide (WO3) nanocolloid particles. The UV-induced photochromic coloration of WO3 nanocolloid particles in the presence of aromatic α-amino acid (AA), l-phenylalanine (Phe) or l-2-phenylglycine (Phg), and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TMβCDx) in an aqueous system was investigated using UV-vis absorption spectrometry. The characteristics of the adsorption modes and configurations of AAs on the WO3 surface have also been identified by using a combination of adsorption isotherm analysis and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). A distinct linear relationship was observed between the concentration of AAs adsorbed on the WO3 nanocolloid particles and the initial photochromic coloration rate in the corresponding UV-irradiated colloidal WO3 in aqueous media, indicating that a simple and sensitive quantification of AAs can be achieved from UV-induced WO3 photochromic coloration without any complicated preprocessing. The proposed colorimetric assay in the Phe/TMβCDx/WO3 ternary aqueous system had a linear range of 1 × 10-8 to 1 × 10-4 mol dm-3 for Phe detection, with a limit of detection of 8.3 × 10-9 mol dm-3. The combined results from UV-vis absorption, ATR-FTIR, and adsorption isotherm experiments conclusively indicated that the TMβCDx-complexed Phe molecules in the Phe/TMβCDx/WO3 ternary aqueous system are preferentially and strongly inner-sphere adsorbed on the WO3 surface, resulting in a more significant surface-enhanced photochromic phenomenon. The findings in this study provided intriguing insights into the design and development of the "label-free" colorimetric assay system based on the surface-enhanced photochromic phenomenon of the WO3 nanocolloid probe.

Evaluating change in diet with pegvaliase treatment in adults with phenylketonuria: Analysis of phase 3 clinical trial data

Phenylketonuria (PKU), a genetic disorder characterized by phenylalanine hydroxylase (PAH) deficiency and phenylalanine (Phe) accumulation, is primarily managed with a protein-restricted diet and PKU-specific medical foods. Pegvaliase is an enzyme substitution therapy approved for individuals with PKU and uncontrolled blood Phe concentrations (>600 μmol/L) despite prior management. This analysis assessed the effect of pegvaliase on dietary intake using data from the Phase 3 PRISM-1 (NCT01819727), PRISM-2 (NCT01889862), and 165-304 (NCT03694353) clinical trials. Participants (N = 250) had a baseline diet assessment, blood Phe ≥600 μmol/L, and had discontinued sapropterin; they were not required to follow a Phe-restricted diet. Outcomes were analyzed by baseline dietary group, categorized as >75%, some (>0% but ≤75%), or no protein intake from medical food. At baseline, mean age was 29.1 years, 49.2% were female, mean body mass index was 28.4 kg/m2, and mean blood Phe was 1237.0 μmol/L. Total protein intake was stable up to 48 months for all 3 baseline dietary groups. Over this time, intact protein intake increased in all groups, and medical protein intake decreased in those who consumed any medical protein at baseline. Of participants consuming some or >75% medical protein at baseline, 49.1% and 34.1% were consuming no medical protein at last assessment, respectively. Following a first hypophenylalaninemia (HypoPhe; 2 consecutive blood Phe measurements <30 μmol/L) event, consumption of medical protein decreased and consumption of intact protein increased. Substantial and sustained Phe reductions were achieved in all 3 baseline dietary groups. The probability of achieving sustained Phe response (SPR) at ≤600 μmol/L was significantly greater for participants consuming medical protein versus no medical protein in an unadjusted analysis, but no statistically significant difference between groups was observed for probability of achieving SPR ≤360 or SPR ≤120 μmol/L. Participants with alopecia (n = 49) had longer pegvaliase treatment durations, reached HypoPhe sooner, and spent longer in HypoPhe than those who did not have alopecia. Most (87.8%) had an identifiable blood Phe drop before their first alopecia episode, and 51.0% (n = 21/41) of first alopecia episodes with known duration resolved before the end of the HypoPhe episode. In conclusion, pegvaliase treatment allowed adults with PKU to lower their blood Phe, reduce their reliance on medical protein, and increase their intact and total protein intake. Results also suggest that HypoPhe does not increase the risk of protein malnutrition in adults with PKU receiving pegvaliase.

Optimization of Phenylalanine Cut-Off Value in Newborn Screening Based on Blood Sampling Time

OBJECTIVE

 The aim of this study was to optimize the cut-off value of phenylalanine (Phe) for phenylketonuria (PKU) screening in Xinjiang Uygur Autonomous Region based on the time of blood sampling.

STUDY DESIGN

 In this study, 110,806 neonates born in 91 obstetrics and gynecology hospitals of Xinjiang Uygur Autonomous Region between June 2017 and December 2019 were divided into two groups (i.e., groups 1 and 2) based on the sampling time. The concentration of Phe was determined using fluorimetric method. The optimization of the Phe cut-off value was conducted using the receiver operating characteristic curve from the treating set involving 80,354 neonates. Then, the diagnostic values of the optimized Phe cut-off value were evaluated using validation set involving 30,452 neonates, based on the comparison of sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) obtained from conventional cut-off value.

RESULTS

 A range of cut-off values was used for preliminary Phe concentrations in the two groups to analyze the sensitivity, specificity, PPV, and NPV. The optimized cut-off value of Phe in group 1 was 2.0, while that in the group 2 was 2.21. A comparison was given to PPV, NPV, sensitivity, and specificity generated by the optimized cut-off value and the conventional cut-off value, which yielded similar sensitivity, specificity, and PPV, and less recalled number of samples.

CONCLUSION

 The optimization of cut-off value of Phe based on sampling time is feasible for PKU screening in Xinjiang Uygur Autonomous Region. In addition, the false positive rate was significantly reduced, which may save more efforts in sample recalling process.

KEY POINTS

· The optimization of Phe cut-off value for Xinjiang Region.. · The optimized cut-off value reduced the recalling samples.. · Our cut-off value is feasible for PKU screening in Xinjiang..

A ratio fluorescence method based on dual emissive gold nanoclusters for detection of biomolecules and metal ions

Gold nanoclusters have good biocompatibility and can be easily modified to improve their luminescence properties. In this study, we prepared a new type of dual-emitting gold nanoclusters (d-Au NCs) for discriminative detection of phenylalanine and Fe³⁺ with high selectivity and sensitivity. The fluorescence sensor which was synthesized without any further assembly or conjugation shows dual-emissions at 430 nm and 600 nm under a single excitation at 350 nm. Phenylalanine can turn on the red emission of the probe, while Fe³⁺ can turn on its yellow emission and turn off the red emission. By detecting a variety of amino acids and metal ions, d-Au NCs showed good selectivity to phenylalanine and Fe³⁺. Finally, this method was applied to determine phenylalanine and Fe³⁺ in lake water, human urine and milk, which has certain application prospects in the field of biology and environment.

Novel dual-emissive gold nanoclusters (d-Au NCs) were prepared and applied for the simultaneous detection of phenylalanine or Fe³⁺.

Phenylketonuria

Phenylketonuria (PKU; also known as phenylalanine hydroxylase (PAH) deficiency) is an autosomal recessive disorder of phenylalanine metabolism, in which especially high phenylalanine concentrations cause brain dysfunction. If untreated, this brain dysfunction results in severe intellectual disability, epilepsy and behavioural problems. The prevalence varies worldwide, with an average of about 1:10,000 newborns. Early diagnosis is based on newborn screening, and if treatment is started early and continued, intelligence is within normal limits with, on average, some suboptimal neurocognitive function. Dietary restriction of phenylalanine has been the mainstay of treatment for over 60 years and has been highly successful, although outcomes are still suboptimal and patients can find the treatment difficult to adhere to. Pharmacological treatments are available, such as tetrahydrobiopterin, which is effective in only a minority of patients (usually those with milder PKU), and pegylated phenylalanine ammonia lyase, which requires daily subcutaneous injections and causes adverse immune responses. Given the drawbacks of these approaches, other treatments are in development, such as mRNA and gene therapy. Even though PAH deficiency is the most common defect of amino acid metabolism in humans, brain dysfunction in individuals with PKU is still not well understood and further research is needed to facilitate development of pathophysiology-driven treatments.

The complete European guidelines on phenylketonuria: diagnosis and treatment

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism caused by deficiency in the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine. If left untreated, PKU results in increased phenylalanine concentrations in blood and brain, which cause severe intellectual disability, epilepsy and behavioural problems. PKU management differs widely across Europe and therefore these guidelines have been developed aiming to optimize and standardize PKU care. Professionals from 10 different European countries developed the guidelines according to the AGREE (Appraisal of Guidelines for Research and Evaluation) method. Literature search, critical appraisal and evidence grading were conducted according to the SIGN (Scottish Intercollegiate Guidelines Network) method. The Delphi-method was used when there was no or little evidence available. External consultants reviewed the guidelines. Using these methods 70 statements were formulated based on the highest quality evidence available. The level of evidence of most recommendations is C or D. Although study designs and patient numbers are sub-optimal, many statements are convincing, important and relevant. In addition, knowledge gaps are identified which require further research in order to direct better care for the future.

Key European guidelines for the diagnosis and management of patients with phenylketonuria

We developed European guidelines to optimise phenylketonuria (PKU) care. To develop the guidelines, we did a literature search, critical appraisal, and evidence grading according to the Scottish Intercollegiate Guidelines Network method. We used the Delphi method when little or no evidence was available. From the 70 recommendations formulated, in this Review we describe ten that we deem as having the highest priority. Diet is the cornerstone of treatment, although some patients can benefit from tetrahydrobiopterin (BH4). Untreated blood phenylalanine concentrations determine management of people with PKU. No intervention is required if the blood phenylalanine concentration is less than 360 μmol/L. Treatment is recommended up to the age of 12 years if the phenylalanine blood concentration is between 360 μmol/L and 600 μmol/L, and lifelong treatment is recommended if the concentration is more than 600 μmol/L. For women trying to conceive and during pregnancy (maternal PKU), untreated phenylalanine blood concentrations of more than 360 μmol/L need to be reduced. Treatment target concentrations are as follows: 120-360 μmol/L for individuals aged 0-12 years and for maternal PKU, and 120-600 μmol/L for non-pregnant individuals older than 12 years. Minimum requirements for the management and follow-up of patients with PKU are scheduled according to age, adherence to treatment, and clinical status. Nutritional, clinical, and biochemical follow-up is necessary for all patients, regardless of therapy.

Neurological and Neuropsychological Problems in Tyrosinemia Type I Patients

Clinically, Hereditary Tyrosinemia type I (HTI) is especially characterized by severe liver dysfunction in early life. However, recurrent neurological crises are another main finding in these patients when they are treated with a tyrosine and phenylalanine restricted diet only. This is caused by the accumulation of δ-aminolevulinic acid due to the inhibitory effect of succinylacetone on the enzyme that metabolizes δ-aminolevulinic acid. Due to the biochemical and clinical resemblance of these neurological crises and acute intermittent porphyria, this group of symptoms in HTI patients is mostly called porphyria-like-syndrome. The neurological crises in HTI patients disappeared after the introduction of treatment with 2-(2 nitro-4-3 trifluoro-methylbenzoyl)-1, 3-cyclohexanedione (NTBC). However, if NTBC treatment is stopped for a while, severe neurological dysfunction will reappear.If NTBC treatment is started early and given continuously, all clinical problems seem to be solved. However, recent research findings indicate that HTI patients have a non-optimal neurocognitive outcome, showing (among others) a lower IQ and impaired executive functioning and social cognition. Unfortunately the exact neuropsychological profile of these HTI patients is not known yet, neither are the exact pathophysiological mechanisms underlying these impairments. It may be hypothesized that the biochemical changes such as high blood tyrosine or low blood phenylalanine concentrations are important in this respect, but an direct toxic effect of NTBC or production of toxic metabolites (that previously characterized the disease before introduction of NTBC) cannot be excluded either. This chapter discusses the neurological and neuropsychological symptoms associated with HTI in detail. An extended section on possible underlying pathophysiological mechanisms of such symptoms is also included.

Effect of dietary regime on metabolic control in phenylketonuria: Is exact calculation of phenylalanine intake really necessary?

Background

A phenylalanine (Phe) restricted dietary management is required in phenylketonuria (PKU) to maintain good metabolic control. Nevertheless, five different models of dietary regimes, which differ in their accuracy of Phe documentation, are used. To investigate the effect of the dietary regime on metabolic control, a multicenter evaluation was performed.

Patients/Methods

149 patients (max. 800 mg Phe-intake/day; 108 children aged 1–9 years and 41 adolescents aged 10–15 years) could be included. They were separated according to age and dietary regime, revealed by a questionnaire on dietary habits. Dietary regimes vary from daily strict calculation of all Phe-intake (group 1) to a rather loose regime only estimating Phe-intake and including high protein food (group 5). Data were analyzed with respect to metabolic control (Phe-concentrations, Phe-concentrations above upper recommended limit during 6 months before the interview), Phe-intake (mg/day) and age (years).

Results

Median Phe-concentrations in children did not differ significantly among diet groups (group 1: 161; 2: 229, 3: 236, 4: 249, 5: 288 μmol/l, p = 0.175). However, exact daily Phe calculation led to significantly lower percentage of Phe concentrations above the upper recommended limit (group 1: 17, 2: 50, 3: 42, 4: 50, 5: 75%, p = 0.035). All included patients showed good to acceptable metabolic control. Patients on the dietary regime with the least accuracy, consuming also high protein foods, showed the poorest metabolic control. Median Phe concentrations of all other groups remained within recommended ranges, including from groups not calculating special low protein foods, fruit and vegetables and using a simplified system of recording Phe-intake.

In adolescents no significant differences among diet groups were revealed.

Conclusion

Exact calculation of Phe content of all food is not necessary to achieve good metabolic control in children and adolescents with PKU. Excluding special low protein food, as well as fruit and vegetables from calculation of Phe-intake has no impact on metabolic control. However including protein rich food into the diet and simply estimating all Phe-intake appears insufficient. The simplification of dietary regime may be helpful in enhancing acceptability and feasibility.

Infants with Tyrosinemia Type 1: Should phenylalanine be supplemented?

Tyrosinemia type 1 (HT1) is an inborn error of tyrosine catabolism caused by fumarylacetoacetase deficiency. Biochemically, this results in accumulation of toxic metabolites including succinylacetone. Clinically, HT1 is characterized by severe liver, kidney, and neurological problems. Treatment with NTBC and dietary restriction of tyrosine and phenylalanine have strongly improved outcome, but impaired neurocognitive development has been reported. Whether impaired neurocognitive outcome results from high blood tyrosine or low blood phenylalanine concentrations is currently unknown. In this report, two HT1 newborns, diagnosed by neonatal screening, are presented. The first patient showed low phenylalanine concentrations, growth retardation, neurological impairments, and skin problems, clearly improving after institution of phenylalanine supplementation (~30 mg/kg/day) at age 6 months, while both blood phenylalanine and tyrosine concentrations increased. In the second patient, phenylalanine supplementation (~20 mg/kg/day) was initiated as soon as low phenylalanine concentrations were observed at age 19 days. On this regimen, blood phenylalanine concentrations increased, and hypophenylalaninemia was less frequently observed than in the first patient, whereas blood tyrosine concentrations tended to increase. Clinically, no growth, neurological, or skin problems have been observed. The combination of knowledge obtained from these cases suggests that hypophenylalaninemia rather than hypertyrosinemia during the first months of life may impair neurocognitive development in young HT1 infants. Phenylalanine supplementation should really be considered in HT1 patients with consistently low blood phenylalanine concentrations during the first months of life. However, the minimal phenylalanine concentrations acceptable and the optimal phenylalanine supplementation regimen require further investigation.