Phenylalanine hydroxylase deficiency

Predictive value of fluorometric method and tandem mass spectrometry for hyperphenylalaninemia and its subtypes in China: A systematic review and meta‑analysis

The present study aimed to conduct a comprehensive meta-analysis to assess the diagnostic value of fluorometric assays and tandem mass spectrometry (MS/MS) for hyperphenylalaninemia (HPA) and its subtypes. The PubMed, Embase and Cochrane Library databases were searched from inception to October 2023. The present study included studies that reported the newborn screening and genetic features of patients with HPA and excluded duplicate publications, studies without full text, studies with incomplete information, studies from which it was not possible to extract data, animal experiments, reviews and systematic reviews. STATA 15.1 was used to analyze the data. The pooled results revealed that 0.04% [95% confidence interval (CI): 0.019-0.069] of neonatal HPA fluorometric assays and MS/MS. The positive predictive value (PPV) of neonatal HPA screening using fluorometric assays and tandem mass spectrometry was 31.7% (95% CI: 19.6-45.2). Notably, the PPV of neonatal HPA screening using fluorometric assays was 8.3% (95% CI: 7.1-9.6), while the PPV of neonatal HPA screening using tandem mass spectrometry was 31.8% (95% CI: 16.4-49.4). Additionally, the pooled results showed that the incidence of tetrahydrobiopterin deficiency (BH4D) in HPA patients was 12.43% (95% CI: 3.28-25.75) and the incidence of phenylalanine hydroxylase deficiency (PAHD) in HPA patients was 88.65% (95% CI: 78.84-95.86). Newborn screening is an effective method for the early detection of HPA and MS/MS has a greater PPA than fluorometric assays for diagnosing HPA. In addition, in the screening of HPA, the proportion of HPA patients with PAHD was significantly higher than that of patients with BH4D.

Significance of utilizing in silico structural analysis and phenotypic data to characterize phenylalanine hydroxylase variants: A PAH landscape

Phenylketonuria (PKU) is a genetic disorder caused by variations in the phenylalanine hydroxylase (PAH) gene. Among the 3369 reported PAH variants, 33.7% are missense alterations. Unfortunately, 30% of these missense variants are classified as variants of unknown significance (VUS), posing challenges for genetic risk assessment. In our study, we focused on analyzing 836 missense PAH variants following the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines specified by ClinGen PAH Variant Curation Expert Panel (VCEP) criteria. We utilized and compared variant annotator tools like Franklin and Varsome, conducted 3D structural analysis of PAH, and examined active and regulatory site hotspots. In addition, we assessed potential splicing effect of apparent missense variants. By evaluating phenotype data from 22962 PKU patients, our aim was to reassess the pathogenicity of missense variants. Our comprehensive approach successfully reclassified 309 VUSs out of 836 missense variants as likely pathogenic or pathogenic (37%), upgraded 370 likely pathogenic variants to pathogenic, and reclassified one previously considered likely benign variant as likely pathogenic. Phenotypic information was available for 636 missense variants, with 441 undergoing 3D structural analysis and active site hotspot identification for 180 variants. After our analysis, only 6% of missense variants were classified as VUSs, and three of them (c.23A>C/p.Asn8Thr, c.59_60delinsCC/p.Gln20Pro, and c.278A >T/p.Asn93Ile) may be influenced by abnormal splicing. Moreover, a pathogenic variant (c.168G>T/p.Glu56Asp) was identified to have a risk exceeding 98% for modifications of the consensus splice site, with high scores indicating a donor loss of 0.94. The integration of ACMG/AMP guidelines with in silico structural analysis and phenotypic data significantly reduced the number of missense VUSs, providing a strong basis for genetic counseling and emphasizing the importance of metabolic phenotype information in variant curation. This study also sheds light on the current landscape of PAH variants.

Emerging biosensors in Phenylketonuria

Phenylketonuria (PKU) is an autosomal recessive metabolic disorder resulting from deficient phenylalanine hydroxylase (PAH) enzyme activity, leading to impaired phenylalanine (Phe) metabolism. This condition can lead to intellectual disability, epilepsy, and behavioural issues. Treatment typically involves strict dietary restrictions on natural protein intake, supplemented with chemically manufactured protein substitutes containing amino acids other than Phe. Various approaches, including casein glycomacropeptide (GMP), tetrahydrobiopterin (BH4), phenylalanine ammonia-lyase (PAL) therapy, large neutral amino acid (LNAA) supplementation, enzyme therapy, gene therapy, and medical therapies, aim to prevent Phe transport in the brain to potentially treat PKU. Although newborn screening programs and early dietary interventions have enhanced outcomes of the potential treatment strategies, limitations still persist in this direction. These involve potent accuracy concerns in diagnosis due to the existence of antibiotics in blood of PKU patients, affecting growth of the bacteria in the bacterial inhibition assay. Monitoring involves complex methods for instance, mass spectrometry and high-pressure liquid chromatography, which involve shortcomings such as lengthy protocols and the need for specialized equipment. To address these limitations, adaptable testing formats like bio/nano sensors are emerging with their cost-effectiveness, biodegradability, and rapid, accurate, and sensitive detection capabilities, offering promising alternatives for PKU diagnosis. This review provides insights into current treatment and diagnostic approaches, emphasizing on the potential applications of the diverse sensors intended for PKU diagnosis.

Unveiling the genetic tapestry: Rare disease genomics of spinal muscular atrophy and phenylketonuria proteins

Rare diseases, defined by their low prevalence, present significant challenges, including delayed detection, expensive treatments, and limited research. This study delves into the genetic basis of two noteworthy rare diseases in Saudi Arabia: Phenylketonuria (PKU) and Spinal Muscular Atrophy (SMA). PKU, resulting from mutations in the phenylalanine hydroxylase (PAH) gene, exhibits geographical variability and impacts intellectual abilities. SMA, characterized by motor neuron loss, is linked to mutations in the survival of motor neuron 1 (SMN1) gene. Recognizing the importance of unveiling signature genomics in rare diseases, we conducted a quantitative study on PAH and SMN1 proteins of multiple organisms by employing various quantitative techniques to assess genetic variations. The derived signature-genomics contributes to a deeper understanding of these critical genes, paving the way for enhanced diagnostics for disorders associated with PAH and SMN1.

Management of patients with phenylketonuria (PKU) under enzyme replacement therapy: An Italian model (expert opinion)

Objective

Phenylketonuria (PKU) is a metabolic disorder necessitating lifelong management to prevent severe neurological impairments. This paper synthesises clinical practices from Italian specialist centres to delineate a unified approach for administering pegvaliase, a novel enzyme replacement therapy for PKU.

Methods

Virtual meetings convened in September 2022, gathering a steering committee (SC) of experts from five Italian centres specialising in PKU. The SC reviewed, and discussed clinical practices, and formulated recommendations for pegvaliase treatment.

Results

The SC outlined a comprehensive treatment roadmap for PKU management with pegvaliase, emphasising the importance of multidisciplinary care teams, patient selection, pre-treatment evaluation, and education. Recommendations include initial hospital-based pegvaliase administration, regular monitoring of phenylalanine and tyrosine levels, dietary adjustments, and management of adverse events. A consensus was reached on the need for a digital database to manage treatment plans and enhance communication between healthcare professionals and patients.

Conclusion

The expert panel's consensus highlights the complexity of PKU management and the necessity for a coordinated, patient-centred approach. The recommendations aim to standardise care across Italian centres and provide a framework for integrating pegvaliase therapy into clinical practice, potentially informing international guidelines. Further research is warranted to evaluate the long-term impact of these practices on patient outcomes and quality of life.

Advancements in food science for Phenylketonuria (PKU) management: a comprehensive review

This review systematically explores the pivotal role of food science and technology as a support for Phenylketonuria (PKU) dietary management. It delves into the genetic and metabolic underpinnings of PKU, highlighting the crucial need for stringent dietary regulation to manage phenylalanine levels and mitigate neurological complications. Through bibliometric analysis and current product evaluations, it identifies trends in PKU food research, emphasizing recent innovations in food formulations such as glycomacropeptide (GMP) supplements and higher appealing low-phenylalanine food products. Furthermore, it accentuates the sensory and consumer aspects of PKU dietary solutions, underscoring the importance of palatability for adherence. Notably, the review introduces 3D food printing as an emerging technology for creating personalized, nutrient-optimized, and sensory-appealing foods for PKU patients, offering a new horizon in dietary management. This comprehensive assessment underscores the dynamic interplay between nutritional science, food technology, and sensory evaluation in improving the quality of life for individuals with PKU.

Comparison of Cost Analysis in Patients with Tetrahydrobiopterin-Responsive and Non-Responsive Phenylketonuria in Turkey

Phenylketonuria is an inherited metabolic disorder that leads to neurobehavioral dysfunction. The main treatment is a low-phenylalanine diet and/or the cofactor tetrahydrobiopterin. Regular outpatient follow-up care and measurement of the phenylalanine levels in the blood are required. We aimed to analyze the economic burden of phenylketonuria on families and the state. The patients with phenylketonuria were divided into three groups according to their treatment: a low-phenylalanine diet group (n = 50), a tetrahydrobiopterin group (n = 44), and a group taking tetrahydrobiopterin together with the diet (n = 25). A comparative cost analysis was carried out. The annual economic burden to the state was calculated to average EUR 18,801 ± 15,345 and was lowest in the diet group, then in the tetrahydrobiopterin group, and highest in the tetrahydrobiopterin + diet group (p < 0.001). Out-of-pocket costs amounted to EUR 1531 ± 1173 per year, and indirect losses averaged EUR 2125 ± 1930 per year for all families. The economic loss was significantly lower in the families taking tetrahydrobiopterin than in the other groups (p = 0.001). The combined use of medical nutrition and BH4 treatments has been shown to increase the economic burden on the state. Reimbursing low-protein products and increasing the number of patients eligible for financial allowances may reduce the economic burden on families.

Alkaptonuria

Alkaptonuria is a rare inborn error of metabolism caused by the deficiency of homogentisate 1,2-dioxygenase activity. The consequent homogentisic acid (HGA) accumulation in body fluids and tissues leads to a multisystemic and highly debilitating disease whose main features are dark urine, ochronosis (HGA-derived pigment in collagen-rich connective tissues), and a painful and severe form of osteoarthropathy. Other clinical manifestations are extremely variable and include kidney and prostate stones, aortic stenosis, bone fractures, and tendon, ligament and/or muscle ruptures. As an autosomal recessive disorder, alkaptonuria affects men and women equally. Debilitating symptoms appear around the third decade of life, but a proper and timely diagnosis is often delayed due to their non-specific nature and a lack of knowledge among physicians. In later stages, patients' quality of life might be seriously compromised and further complicated by comorbidities. Thus, appropriate management of alkaptonuria requires a multidisciplinary approach, and periodic clinical evaluation is advised to monitor disease progression, complications and/or comorbidities, and to enable prompt intervention. Treatment options are patient-tailored and include a combination of medications, physical therapy and surgery. Current basic and clinical research focuses on improving patient management and developing innovative therapies and implementing precision medicine strategies.

Roles of the N-terminal motif in improving the activity and soluble expression of phenylalanine ammonia lyases in Escherichia coli

Phenylalanine ammonia-lyase (PAL) has various applications in fine chemical manufacturing and the pharmaceutical industry. In particular, PAL derived from Anabaena variabilis (AvPAL) is used as a therapeutic agent to the treat phenylketonuria in clinical settings. In this study, we aligned the amino acid sequences of AvPAL and PAL derived from Nostoc punctiforme (NpPAL) to obtain several mutants with enhanced activity, expression yield, and thermal stability via amino acid substitution and saturation mutagenesis at the N-terminal position. Enzyme kinetic experiments revealed that the kcat values of NpPAL-N2K, NpPAL-I3T, and NpPAL-T4L mutants were increased to 3.2-, 2.8-, and 3.3-fold that of the wild-type, respectively. Saturation mutagenesis of the fourth amino acid in AvPAL revealed that the kcat values of AvPAL-L4N, AvPAL-L4P, AvPAL-L4Q and AvPAL-L4S increased to 4.0-, 3.7-, 3.6-, and 3.2-fold, respectively. Additionally, the soluble protein yield of AvPAL-L4K increased to approximately 14 mg/L, which is approximately 3.5-fold that of AvPAL. Molecular dynamics studies further revealed that maintaining the attacking state of the reaction and N-terminal structure increased the rate of catalytic reaction and improved the solubility of proteins. These findings provide new insights for the rational design of PAL in the future.

Intake Modalities of Amino Acid Supplements: A Real-World Data Collection from Phenylketonuria Patients

BACKGROUND

To achieve a normal nutritional status, patients suffering from phenylketonuria (PKU) are typically prescribed amino acid (AA) supplements with low or no phenylalanine (Phe) content. Studies evaluating patient preferences regarding the intake modalities of AA supplements are limited. This study aimed to collect real-world data regarding prescription adherence and intake modalities of AA supplements reported by PKU patients while monitoring metabolic control.

METHODS

This cross-sectional study included 33 PKU patients (16 female and 17 male) with a mean age of 27.2 years. Questionnaires were provided to assess information on AA supplement intake, such as prescription adherence rate, frequency and timing of administration, supplement formulation, and combination with food or drinks. Plasma phenylalanine levels were monitored during the study period.

RESULTS

51.5% (n = 17) of patients reported to lay within an adherence range of 75-100%. The majority of patients consumed AA supplements twice daily, with breakfast (87.9%) and afternoon snacks (51.5%). Powder supplements were most commonly used (72.7%) and often combined with milk and/or fruit juices (45.4%).

CONCLUSIONS

Despite the known concerns related to treatment compliance among PKU adolescents and adults, most of the study participants reported a high level of adherence to AA supplement prescription. The personalized dietary regimens followed by the patients included in the current study represent a treatment approach that might be worth trying in non-compliant patients.

[In vitro expression and functional analyses of the mutants p.R243Q, p.R241C and p.Y356X of the human phenylalanine hydroxylase]

OBJECTIVES

To study the in vitro expression of three phenylalanine hydroxylase (PAH) mutants (p.R243Q, p.R241C, and p.Y356X) and determine their pathogenicity.

METHODS

Bioinformatics techniques were used to predict the impact of PAH mutants on the structure and function of PAH protein. Corresponding mutant plasmids of PAH were constructed and expressed in HEK293T cells. Quantitative reverse transcription polymerase chain reaction was used to measure the mRNA expression levels of the three PAH mutants, and their protein levels were assessed using Western blot and enzyme-linked immunosorbent assay.

RESULTS

Bioinformatics analysis predicted that all three mutants were pathogenic. The mRNA expression levels of the p.R243Q and p.R241C mutants in HEK293T cells were similar to the mRNA expression level of the wild-type control (P>0.05), while the mRNA expression level of the p.Y356X mutant significantly decreased (P<0.05). The PAH protein expression levels of all three mutants were significantly reduced compared to the wild-type control (P<0.05). The extracellular concentration of PAH protein was reduced in the p.R241C and p.Y356X mutants compared to the wild-type control (P<0.05), while there was no significant difference between the p.R243Q mutant and the wild type control (P>0.05).

CONCLUSIONS

p.R243Q, p.R241C and p.Y356X mutants lead to reduced expression levels of PAH protein in eukaryotic cells, with p.R241C and p.Y356X mutants also affecting the function of PAH protein. These three PAH mutants are to be pathogenic.

DNAJC12 in Monoamine Metabolism, Neurodevelopment, and Neurodegeneration

Recent studies show that pathogenic variants in DNAJC12, a co-chaperone for monoamine synthesis, may cause mild hyperphenylalaninemia with infantile dystonia, young-onset parkinsonism, developmental delay and cognitive deficits. DNAJC12 has been included in newborn screening, most revealingly in Spain, and those results highlight the importance of genetic diagnosis and early intervention in combating human disease. However, practitioners may be unaware of these advances and it is probable that many patients, especially adults, have yet to receive molecular testing for DNAJC12. Hence, this review summarizes genotype-phenotype relationships and treatment paradigms for patients with pathogenic variants in DNAJC12. It provides an overview of the structure of DNAJC12 protein, known genetic variants, domains, and binding partners, and elaborates on its role in monoamine synthesis, disease etiology, and pathogenesis. © 2023 International Parkinson and Movement Disorder Society.

Construction of an ultrasensitive dual-mode chiral molecules sensing platform based on molecularly imprinted polymer modified bipolar electrode

Chiral molecules are abundant in nature. Phenylketonuria (PKU) is caused by the abnormal transformation of chiral molecules L-phenylalanine (L-Phe) in the human blood, which can cause irreversible harm to the human body. In this work, we documented an electrochemiluminescent (ECL) dual-mode sensor platform based on molecularly imprinted polymer (MIP) modified closed bipolar electrodes for high sensitivity detection of L-Phe and D-phenylalanine (D-Phe). In the anode chamber of a bipolar electrode modified with phenylalanine imprinting, Ru (bpy)32+ underwent a redox reaction to produce a chemiluminescence response under the stimulation of a driving voltage. At the same time, the reduction of the cathode film of the bipolar electrode was promoted, and the color changed from dark blue to nearly white. Thus, the dual-mode detection of target molecules is realized. The detection range of the sensor for phenylalanine reached 0.01-10,000 nM, and the detection limits of L-Phe and D-Phe were 3.9 pM and 4.6 pM (S/N = 3), respectively. This dual-mode system achieved high stability and high specificity, and also successfully realized the detection of actual samples, which is expected to achieve future clinical applications.

Analysis of gene variation and long-term follow-up in children with phenylalanine hydroxylase deficiency diagnosed by newborn screening

OBJECTIVES

To retrospectively analyze the variation and characteristics of phenylalanine hydroxylase (PAH) gene, and to observe the long-term treatment effect and follow-up of newborns with PAH deficiency.

METHODS

Clinical data, treatment and follow-up results of 198 patients with PAH deficiency diagnosed by newborn screening in Jinan from 1996 to 2021 were collected. The genetic analysis of 55 patients with PAH deficiency diagnosed by newborn screening in Jinan and 213 patients referred from the surrounding areas of Jinan were summarized. Gene variations were checked by a customized Panel gene detection method. Blood phenylalanine-concentration and physical development indicators including height and weight were regularly monitored. Intellectual development was assessed using a neuropsychological development scale for patients aged 0-6 years and academic performance, and brain injury in patients was assessed using brain magnetic resonance imaging.

RESULTS

c.728G>A, c.158G>A, c.721C>T, c.1068C>A, c.611A>G variations were common in PAH gene. The genotype of c.158G>A variation is compound heterozygous variation, with mainly a mild hyperpheny-lalaninemia. 168 patients with PAH deficiency who were followed-up regularly had normal physical development without dwarfism or malnutrition. Among the 33 preschool patients who underwent mental development assessment, 2 were mentally retarded and the initial treatment age was older than 6 months. Nine patients with an average age of (17.13±2.42) years completed brain magnetic resonance imaging, one case was normal, and 8 cases were abnormal. There were patchy or patchy hyperintense foci near the bilateral lateral ventricles on T2WI, and the intellectual development was normal. Compared with the other eight patients, the blood phenylalanine concentration of the normal child was better and stably controlled within the ideal range.

CONCLUSIONS

c.728G>A, c.158G>A, c.721C>T, c.1068C>A, c.611A>G variations were common in PAH gene. After standardized treatment, most patients with PAH deficiency diagnosed by screening can obtain normal growth and intellectual development in adolescence, but there are different degrees of organic lesions in the cerebral white matter.

Pharmacodynamics, safety, tolerability and pharmacokinetics of a single oral dose of an engineered phenylalanine ammonia-lyase in patients with phenylketonuria

The cornerstone treatment of hyperphenylalaninemia (HPA) and phenylketonuria (PKU) is a lifelong low-protein diet with phenylalanine (Phe) free L-amino acid supplements. However, the PKU diet has significant shortcomings, and there is a clinically unmet need for new therapeutics to improve patient outcomes. CDX-6114 is a modified phenylalanine ammonia-lyase (PAL) enzyme obtained by a mutation in the Anabaena variabilis PAL sequence. CodeEvolver® protein engineering technology has been applied to improve the degradation resistance of the enzyme. In our first phase I trial, 19 patients were given a single oral dose of CDX-6114 at 7.5 g, 2.5 g, 0.7 g, or placebo in a cross-over design. After an overnight fast, patients received a standardised breakfast of 20 g of protein, thus exceeding the dietary recommendations for a single meal in patients with PKU. Plasma levels of Phe and cinnamic acid (CA) were measured over a 5-h period following CDX-6114 dosing. During the development of CDX-6114, a stability assessment using reverse-phase high-performance liquid chromatography (HPLC) assay revealed two peaks. The second peak was identified as CA. It was not previously known that as part of the mechanism of action, the CA remained associated with the protein following the conversion of Phe. Thus, recalculating the historical PAL enzyme amounts in CDX-6114 bulk substance was necessary. An updated extinction coefficient was achieved by applying a correction factor of 0.771 to previously reported doses. Postprandial plasma levels of Phe increased in all dose cohorts over time between 10% and 30% from baseline, although the actual peak of Phe levels was not achieved within the 5-h observation. When accounting for the interquartile ranges, these concentrations were similar to the placebo. As plasma levels of Phe were no longer a reliable marker for pharmacodynamics, the consistently detectable amount of CA seen in all patients who received CDX-6114 provided proof of the enzymatic activity of CDX-6114 in metabolising gastrointestinal Phe. Peak levels of CA were seen shortly after CDX-6114 intake, with a rapid decline, and remained low compared with the plasma Phe levels. This pattern indicates a short half-life, possibly due to the liquid formulation or the inability to withstand the lower pH in the human stomach compared with animal models in earlier studies. This was the first trial in patients with PKU to establish the safety and tolerability of CDX-6114. A single dose of CDX-6114 was safe and well tolerated, with no serious adverse events or presence of anti-drug antibodies detected. Efficacy will be explored in future trials using an optimised formulation.

Mutational landscape of phenylketonuria in Iran

To date more than 1000 different variants in the PAH gene have been identified in patients with phenylketonuria (PKU). In Iran, several studies have been performed to investigate the genetics bases of the PKU in different parts of the country. In this study, we have analysed and present an update of the mutational landscape of the PAH gene as well as the population genetics and frequencies of detected variants for each cohort. Published articles on PKU mutations in Iran were identified through a comprehensive PubMed, Google Scholar, Web of Science (ISI), SCOPUS, Elsevier, Wiley Online Library and SID literature search using the terms: "phenylketonuria", "hyperphenylalaninemia", and "PKU" in combination with "Iran", "Iranian population", "mutation analysis", and "Molecular genetics". Among the literature-related to genetics of PKU, 18 studies were on the PKU mutations. According to these studies, in different populations of Iran 1497 patients were included for mutation detection that resulted in detection of 129 different mutations. Results of genetic analysis of the different cohorts of Iranian PKU patients show that the most prevalent mutation in Iran is the pathogenic splice variant c.1066-11G > A, occurring in 19.54% of alleles in the cohort. Four other common mutations were p.Arg261Gln, p.Pro281Leu, c.168 + 5G > C and p.Arg243Ter (8.18%, 6.45%, 5.88% and 3.7%, respectively). One notable feature of the studied populations is its high rate of consanguineous marriages. Considering this feature, determining the prevalent PKU mutations could be advantageous for designing screening and diagnostic panels in Iran.

Neuropsychiatric Function Improvement in Pediatric Patients with Phenylketonuria

OBJECTIVE

To evaluate effects of sapropterin dihydrochloride on blood phenylalanine (Phe) and symptoms of neuropsychiatric impairment in children and adolescents with phenylketonuria (PKU).

STUDY DESIGN

PKU subjects 8-17 years of age (n = 86) were randomized to double-blind treatment with sapropterin (n = 43) or placebo (n = 43) for 13 weeks, then all received open-label sapropterin therapy for an additional 13 weeks. Blood Phe and symptoms of inattention, hyperactivity/impulsivity (Attention-Deficit/Hyperactivity Disorder Rating Scale IV [ADHD RS-IV]), executive functioning (Behavior Rating Inventory of Executive Function), depression (Hamilton Rating Scale for Depression), and anxiety (Hamilton Rating Scale for Anxiety) were assessed.

RESULTS

Following the 13-week randomization phase, the sapropterin and placebo groups had mean changes in blood Phe of -20.9% and +2.9%, respectively. Corresponding least square mean differences in ADHD RS-IV scores were significantly greater for the sapropterin vs the placebo group: Total (-3.2 points, P = .02), Inattention subscale (-1.8 points, P = .04), and Hyperactivity/Impulsivity subscale (-1.6 points, P = .02). Forest plots favored sapropterin treatment over placebo for all ADHD RS-IV and Behavior Rating Inventory of Executive Function indices. There were no significant differences in reported problems with attention or executive function between the 2 groups at baseline or at week 26 following the 13-week open-label treatment period. Anxiety and depression scores did not differ significantly between cohorts at any time. Sapropterin was well tolerated, with a favorable safety profile.

CONCLUSIONS

Sapropterin reduced blood Phe and was associated with significant improvement in parent-reported symptoms of inattention, hyperactivity/impulsivity, and executive functioning in children and adolescents with PKU.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01114737. Registered 27 April 2010, https://clinicaltrials.gov/ct2/show/NCT01114737.

Phenylketonuria and the brain

Classic phenylketonuria (PKU) is caused by defective activity of phenylalanine hydroxylase (PAH), the enzyme that coverts phenylalanine (Phe) to tyrosine. Toxic accumulation of phenylalanine and its metabolites, left untreated, affects brain development and function depending on the timing of exposure to elevated levels. The specific mechanisms of Phe-induced brain damage are not completely understood, but they correlate to phenylalanine levels and on the stage of brain growth. During fetal life, high levels of phenylalanine such as those seen in maternal PKU can result in microcephaly, neuronal loss and corpus callosum hypoplasia. Elevated phenylalanine levels during the first few years of life can cause acquired microcephaly, severe cognitive impairment and epilepsy, likely due to the impairment of synaptogenesis. During late childhood, elevated phenylalanine can cause alterations in neurological functioning, leading to ADHD, speech delay and mild IQ reduction. In adolescents and adults, executive function and mood are affected, with some of the abnormalities reversed by better control of phenylalanine levels. Altered brain myelination can be present at this stage. In this article, we review the current knowledge about the consequences of high phenylalanine levels in PKU patients and animal models through different stages of brain development and its effect on cognitive, behavioural and neuropsychological function.

Protein Synthesis Determined from Non-Radioactive Phenylalanine Incorporated by Antarctic Fish

Direct measurements of temperature-dependent weight gains are experimentally challenging and time-consuming in long-lived/slow-growing organisms such as Antarctic fish. Here, we reassess methodology to quantify the in vivo protein synthesis rate from amino acids, as a key component of growth. We tested whether it is possible to avoid hazardous radioactive materials and whether the analytical pathway chosen is robust against analytical errors. In the eelpout, Pachycara brachycephalum, 13C9H1115N1O2 phenylalanine was injected intraperitoneally and muscle tissue was sampled before injection and at 1.5 h time intervals up to 6 h thereafter. The incorporation of 13C15N-labeled-phenylalanine into muscle was monitored by quantification of bound and free phenylalanine through liquid chromatography–mass spectrometry. We found an increase in the pool of labeled, free phenylalanine in the cytosolic fraction that leveled off after 4.5 h. The labeled phenylalanine bound in the proteins increased linearly over time. The resulting protein synthesis rate (Ks) for P. brachycephalum was as low as 0.049 ± 0.021% day−1. This value and its variability were in good agreement with literature data obtained from studies using radioactive labels, indicating that this methodology is well suited for characterizing growth in polar fish under in situ conditions in remote areas or on research vessels.

Incidental molecular diagnoses and heterozygous risk alleles in a carrier screening cohort

PURPOSE

Expanded pan-ethnic carrier screening is an effective tool for the management of reproductive risk. However, growth in the number of conditions screened, in combination with increasingly more comprehensive test methodologies, can lead to the detection of genetic findings that may affect the health of the tested individual. The objective of this study was to investigate the frequency of pathogenic genotypes in a presumed healthy carrier screening cohort to facilitate broader discussions regarding disclosure of genetic information from carrier screening.

METHODS

A retrospective analysis of 73,755 targeted carrier screens was performed to identify individuals with pathogenic genotypes and heterozygous risk alleles.

RESULTS

In this study, we identified 79 individuals (0.11%) with pathogenic genotypes associated with moderate to profound autosomal recessive or X-linked conditions. In addition, 10 cases had chromosome X dosage abnormalities suggestive of a sex chromosome abnormality. Heterozygote risk alleles represented the majority of ancillary findings in this cohort, including 280 female carriers of FMR1 premutation alleles, 15 heterozygous females with pathogenic DMD variants, and 174 heterozygotes with pathogenic variants in genes that may confer increased risk for somatic malignancies in the heterozygous state.

CONCLUSION

These data suggest that nearly 1% of individuals undergoing carrier screening will have a finding that may require clinical evaluation or surveillance.

mRNA in the Context of Protein Replacement Therapy

Protein replacement therapy is an umbrella term used for medical treatments that aim to substitute or replenish specific protein deficiencies that result either from the protein being absent or non-functional due to mutations in affected patients. Traditionally, such an approach requires a well characterized but arduous and expensive protein production procedure that employs in vitro expression and translation of the pharmaceutical protein in host cells, followed by extensive purification steps. In the wake of the SARS-CoV-2 pandemic, mRNA-based pharmaceuticals were recruited to achieve rapid in vivo production of antigens, proving that the in vivo translation of exogenously administered mRNA is nowadays a viable therapeutic option. In addition, the urgency of the situation and worldwide demand for mRNA-based medicine has led to an evolution in relevant technologies, such as in vitro transcription and nanolipid carriers. In this review, we present preclinical and clinical applications of mRNA as a tool for protein replacement therapy, alongside with information pertaining to the manufacture of modified mRNA through in vitro transcription, carriers employed for its intracellular delivery and critical quality attributes pertaining to the finished product.

Expert opinion of an Italian working group on the assessment of cognitive, psychological, and neurological outcomes in pediatric, adolescent, and adult patients with phenylketonuria

Phenylketonuria (PKU) is an inherited metabolic disease characterized by a defective conversion of phenylalanine (Phe) to tyrosine, potentially leading to Phe accumulation in the brain. Dietary restriction since birth has led to normal cognitive development. However, PKU patients can still develop cognitive or behavioral abnormalities and subtle neurological deficits. Despite the increasing evidence in the field, the assessment of neurocognitive, psychopathological, and neurological follow-up of PKU patients at different ages is still debated. The high interindividual variability in the cognitive outcome of PKU patients makes the specificity of the neurocognitive and behavioral assessment extremely challenging. In the present paper, a multidisciplinary panel of Italian PKU experts discussed different tools available for cognitive, psychopathological, and neurological assessment at different ages based on the existing literature and daily clinical practice. This study aims to provide evidence and a real-life-based framework for a specific clinical assessment of pediatric, adolescent, and adult patients affected by PKU.

Allergy Electronic Health Record Documentation: A 2022 Work Group Report of the AAAAI Adverse Reactions to Drugs, Biologicals, and Latex Committee

The allergy section of the electronic health record (EHR) is ideally reviewed and updated by health care workers during routine outpatient visits, emergency room visits, inpatient hospitalizations, and surgical procedures. This EHR section has the potential to help proactively and comprehensively avoid exposures to drugs, contact irritants, foods, and other agents for which, based on an individual's medical history and/or genetics, there is increased risk for adverse outcomes with future exposures. Because clinical decisions are made and clinical decision support is triggered based on allergy details from the EHR, the allergy module needs to provide meaningful, accurate, timely, and comprehensive allergy information. Although the allergy section of the EHR must meet these requirements to guide appropriate clinical decisions and treatment plans, current EHR allergy modules have not achieved this standard. We urge EHR vendors to collaborate with allergists to optimize and modernize allergy documentation. A work group within the Adverse Reactions to Drugs, Biologicals, and Latex Committee of the American Academy of Allergy, Asthma & Immunology was formed to create recommendations for allergy documentation in the EHR. Whereas it is recognized that the term "allergy" is often used incorrectly because most adverse drug reactions (ADRs) are not true immune-mediated hypersensitivity reactions, "allergy" in this article includes allergies and hypersensitivities as well as side effects and intolerances. Our primary objective is to provide guidance for the current state of allergy documentation in the EHR. This guidance includes clarification of the definition of specific ADR types, reconciliation of confirmed ADRs, and removal of disproved or erroneous ADRs. This document includes a proposal for the creation, education, and implementation of a drug allergy labeling system that may allow for more accurate EHR documentation for improved patient safety.

Dysmyelination and glycolipid interference caused by phenylalanine in phenylketonuria

Phenylketonuria (PKU) is a metabolic disorder connected to an excess of phenylalanine (Phe) in the blood and tissues, with neurological consequences. The disease's molecular bases seem to be related to the accumulation of Phe at the cell membrane surface. Radiological outcomes in the brain demonstrate decreased water diffusivity in white matter, involving axon dysmyelination of not yet understood origin. We used a biophysical approach and model membranes to extend our knowledge of Phe-membrane interaction by clarifying Phe's propensity to affect membrane structure and dynamics based on lipid composition, with emphasis on modulating cholesterol and glycolipid components to mimic raft domains and myelin sheath membranes. Phe showed affinity for the investigated membrane mimics, mainly affecting the Phe-facing membrane leaflet. The surfaces of our neuronal membrane raft mimics were strong anchoring sites for Phe, showing rigidifying effects. From a therapeutic perspective, we further investigated the role of doxycycline, known to disturb Phe packing, unveiling its action as a competitor in Phe interactions with the membrane, suggesting its potential for treatment in the early stages of PKU. Our results suggest how Phe accumulation in extracellular fluids can impede normal growth of myelin sheaths by interfering with membrane slipping and by remodulating free water and myelin-associated water contents.

Genetic etiology and clinical challenges of phenylketonuria

This review discusses the epidemiology, pathophysiology, genetic etiology, and management of phenylketonuria (PKU). PKU, an autosomal recessive disease, is an inborn error of phenylalanine (Phe) metabolism caused by pathogenic variants in the phenylalanine hydroxylase (PAH) gene. The prevalence of PKU varies widely among ethnicities and geographic regions, affecting approximately 1 in 24,000 individuals worldwide. Deficiency in the PAH enzyme or, in rare cases, the cofactor tetrahydrobiopterin results in high blood Phe concentrations, causing brain dysfunction. Untreated PKU, also known as PAH deficiency, results in severe and irreversible intellectual disability, epilepsy, behavioral disorders, and clinical features such as acquired microcephaly, seizures, psychological signs, and generalized hypopigmentation of skin (including hair and eyes). Severe phenotypes are classic PKU, and less severe forms of PAH deficiency are moderate PKU, mild PKU, mild hyperphenylalaninaemia (HPA), or benign HPA. Early diagnosis and intervention must start shortly after birth to prevent major cognitive and neurological effects. Dietary treatment, including natural protein restriction and Phe-free supplements, must be used to maintain blood Phe concentrations of 120-360 μmol/L throughout the life span. Additional treatments include the casein glycomacropeptide (GMP), which contains very limited aromatic amino acids and may improve immunological function, and large neutral amino acid (LNAA) supplementation to prevent plasma Phe transport into the brain. The synthetic BH4 analog, sapropterin hydrochloride (i.e., Kuvan®, BioMarin), is another potential treatment that activates residual PAH, thus decreasing Phe concentrations in the blood of PKU patients. Moreover, daily subcutaneous injection of pegylated Phe ammonia-lyase (i.e., pegvaliase; PALYNZIQ®, BioMarin) has promised gene therapy in recent clinical trials, and mRNA approaches are also being studied.

Oral administration of phenylalanine molecularly imprinted polymer (MIP) benefits PKU mouse model

Phenylketonuria (PKU) is a rare genetic disorder caused by a defect in the metabolism of phenylalanine (Phe). Currently, the most commonly used treatment for PKU is dietary Phe restriction. Problems associated with Phe restricted diets include lack of universal availability, high treatment costs, and reduced adherence to continued treatment with age and finally the development of psychological and neurological problems in a significant proportion of patients despite early start of treatment. One possible approach to decreasing blood Phe level, is inhibition of GI tract absorption of this amino acid. We had previously shown that a Phe selective molecularly imprinted polymer was able to bind Phe in the GI tract and attenuate its plasma concentration. In this work, we used different orally administered Phe selective molecularly imprinted polymer doses in a PKU mouse model to further study the effects of this treatment on biochemical profile and cognitive function in test animals. Treatments started 21 days postnatally. After 3 weeks, brain and plasma amino acid profiles and brain monoaminergic neurotransmitter concentrations were measured. Behavioral profile was also evaluated. Treatment with 2% and 5% Phe selective molecularly imprinted polymer significantly reduced levels of blood Phe in PKU model animals (46% and 48% respectively) meanwhile levels of other amino acids remained unchanged. Brain dopamine concentrations in hippocampus was effectively restored by supplementation of Phe selective molecularly imprinted polymer. Finally, polymer treatment improved locomotor dysfunction in PKU model animals. Our data suggest that the Phe selective molecularly imprinted polymer can be a new candidate for treatment of PKU patients. Take home message: Orally administered Phenylalanine Selective Molecularly Imprinted Polymer is able to inhibit absorption of phenylalanine from the GI tract and may offer a new treatment, in conjunction with dietary restriction, for PKU patients.

Allelic dropout in PAH affecting the results of genetic diagnosis in phenylketonuria

OBJECTIVES

Phenylketonuria (PKU) is an inherited autosomal recessive disorder of phenylalanine metabolism. It is mainly caused by a deficiency in phenylalanine hydroxylase (PAH) and frequently diagnosed with Sanger sequencing. To some extent, allelic dropout can explain the inconsistency in genotype and phenotype.

METHODS

Three families were evaluated through DNA sequence analysis, multiplex ligation-dependent probe amplification (MLPA) and prenatal diagnosis technologies. The possibility of inconsistency in phenotype and genotype with c.331C>T variant was analysed.

RESULTS

Through pedigree analysis, three mothers carried a homozygous c.331C>T variant, which was a false-positive result. New primers were used, and this error was caused by allelic dropout. In this case, c.158G>A was likely a benign variant.

CONCLUSIONS

Sequence variants in primer-binding regions could cause allelic dropout, creating unpredictable errors in genotyping. Our results emphasised the need for careful measures to treat genotype-phenotype inconsistencies.

Evaluation of the Consumption of Fruits and Vegetables by Phenylketonurics in the Metabolic Control of Phenylalanine: An Integrative Review

Phenylketonuria (PKU) is an autosomal recessive disease caused by variants in the gene that encodes phenylalanine hydroxylase (PAH), limiting the metabolism of phenylalanine (Phe). When PAH activity is absent or hindered, Phe is not converted to tyrosine, leading to an accumulation of Phe in the blood, which can cause serious neurological complications. Once PKU is diagnosed, treatment should be started immediately, and the basis for this is dietary restriction of foods with high levels of Phe, associated with the use of protein substitutes and intake of foods with low protein content. This restriction accompanies patients throughout their lives, making their diets unpalatable and monotonous, which represents a major challenge for health professionals and patients, considering that these factors favor food transgression. In this context, the objective of this work was to carry out an integrative review based on evidence regarding the intake of fruits and vegetables, by phenylketonurics, taking into account the greater or lesser tolerance to Phe. Since, some researchers have dedicated themselves to evaluating the biochemical effect of unrestricted consumption of fruits and vegetables at PKU, unifying the information in this regard. It was observed that the intake of vegetable protein by patients with PKU has shown to be promising since the studies indicate that the intake of these proteins does not present adverse effects to the metabolic control of the Phe.

In vivo prime editing of a metabolic liver disease in mice

Prime editing is a highly versatile CRISPR-based genome editing technology that works without DNA double-strand break formation. Despite rapid technological advances, in vivo application for the treatment of genetic diseases remains challenging. Here, we developed a size-reduced SpCas9 prime editor (PE) lacking the RNaseH domain (PE2^ΔRnH) and an intein-split construct (PE2 p.1153) for adeno-associated virus-mediated delivery into the liver. Editing efficiencies reached 15% at the Dnmt1 locus and were further elevated to 58% by delivering unsplit PE2^ΔRnH via human adenoviral vector 5 (AdV). To provide proof of concept for correcting a genetic liver disease, we used the AdV approach for repairing the disease-causing Pah^enu2 mutation in a mouse model of phenylketonuria (PKU) via prime editing. Average correction efficiencies of 11.1% (up to 17.4%) in neonates led to therapeutic reduction of blood phenylalanine, without inducing detectable off-target mutations or prolonged liver inflammation. Although the current in vivo prime editing approach for PKU has limitations for clinical application due to the requirement of high vector doses (7 × 10¹⁴ vg/kg) and the induction of immune responses to the vector and the PE, further development of the technology may lead to curative therapies for PKU and other genetic liver diseases.

The Utility of Genomic Testing for Hyperphenylalaninemia

Hyperphenylalaninemia (HPA), the most common amino acid metabolism disorder, is caused by defects in enzymes involved in phenylalanine metabolism, with the consequent accumulation of phenylalanine and its secondary metabolites in body fluids and tissues. Clinical manifestations of HPA include mental retardation, and its early diagnosis with timely treatment can improve the prognosis of affected patients. Due to the genetic complexity and heterogeneity of HPA, high-throughput molecular technologies, such as next-generation sequencing (NGS), are becoming indispensable tools to fully characterize the etiology, helping clinicians to promptly identify the exact patients’ genotype and determine the appropriate treatment. In this review, after a brief overview of the key enzymes involved in phenylalanine metabolism, we represent the wide spectrum of genes and their variants associated with HPA and discuss the utility of genomic testing for improved diagnosis and clinical management of HPA.

Spectrum Analysis of Inherited Metabolic Disorders for Expanded Newborn Screening in a Central Chinese Population

Neonatal inherited metabolic disorders (IMDs) are closely associated with early neonatal death and abnormal growth and development. Increasing attention has been paid to IMDs because of their high incidence and diversity. However, there are no reports about the incidence of IMDs in Changsha, China. Therefore, we retrospectively analyzed the screening results of neonates to evaluate the characteristics of IMDs in the area. From January 2016 to December 2020, 300,849 neonates were enrolled for expanded newborn screening by tandem mass spectrometry in the Neonatal Disease Screening Center of the Changsha Hospital for Maternal & Child Health Care. Newborns with mild initial results were recalled for repeated tests; if the second test was still positive, the patient was referred for confirmatory tests. A total of 71 confirmed cases were identified in our study, with an incidence rate of 1:4,237. There were 28 cases of amino acid metabolic disorders, representing 39.44% of the IMDs diagnosed, with an incidence rate of 1:10,745. Twelve newborns were diagnosed with organic acid metabolic disorders, accounting for 16.66% of IMDs, with an incidence rate of 1:25,071. There were 31 cases of fatty acid oxidation disorders, representing 43.05% of IMDs, with an incidence rate of 1:9,705. Overall, 14 types of IMDs were found in Changsha. The most common disorders in the region were primary carnitine deficiency, hyperphenylalaninemia and short-chain acyl-CoA dehydrogenase deficiency. Their incidence rate is respectively 1:13,675, 1:16,714 and 1:42,978. The mutations in PAH, SLC22A5, and ACADS are the leading causes of IMDs in this area. This study demonstrates the importance of utilizing MS/MS in IMD screening for early diagnosis and treatment. This strategy may be used for prenatal genetic counseling to avoid irreversible growth and intellectual development disorders in children.

Microcephaly in Neurometabolic Diseases

Neurometabolic disorders are an important group of diseases that mostly occur in neonates and infants. They are mainly due to the lack or dysfunction of an enzyme or cofactors necessary for a specific biochemical reaction, which leads to a deficiency of essential metabolites in the brain. This, in turn, can cause certain neurometabolic diseases. Disruption of metabolic pathways, and the inhibition at earlier stages, may lead to the storage of reaction intermediates, which are often toxic to the developing brain. Symptoms are caused by the progressive deterioration of mental, motor, and perceptual functions. The authors review the diseases with microcephaly, which may be one of the most visible signs of neurometabolic disorders.

The effect of casein glycomacropeptide versus free synthetic amino acids for early treatment of phenylketonuria in a mice model

Introduction

Management of phenylketonuria (PKU) is mainly achieved through dietary control with limited intake of phenylalanine (Phe) from food, supplemented with low protein (LP) food and a mixture of free synthetic (FS) amino acids (AA) (FSAA). Casein glycomacropeptide (CGMP) is a natural peptide released in whey during cheese making by the action of the enzyme chymosin. Because CGMP in its pure form does not contain Phe, it is nutritionally suitable as a supplement in the diet for PKU when enriched with specific AAs. Lacprodan^® CGMP-20 (= CGMP) used in this study contained only trace amounts of Phe due to minor presence of other proteins/peptides.

Objective

The aims were to address the following questions in a classical PKU mouse model: Study 1, off diet: Can pure CGMP or CGMP supplemented with Large Neutral Amino Acids (LNAA) as a supplement to normal diet significantly lower the content of Phe in the brain compared to a control group on normal diet, and does supplementation of selected LNAA results in significant lower brain Phe level?. Study 2, on diet: Does a combination of CGMP, essential (non-Phe) EAAs and LP diet, provide similar plasma and brain Phe levels, growth and behavioral skills as a formula which alone consist of FSAA, with a similar composition?.

Material and methods

45 female mice homozygous for the Pah^enu2 mutation were treated for 12 weeks in five different groups; G1(N-CGMP), fed on Normal (N) casein diet (75%) in combination with CGMP (25%); G2 (N-CGMP-LNAA), fed on Normal (N) casein diet (75%) in combination with CGMP (19,7%) and selected LNAA (5,3% Leu, Tyr and Trp); G3 (N), fed on normal casein diet (100%); G4 (CGMP-EAA-LP), fed on CGMP (70,4%) in combination with essential AA (19,6%) and LP diet; G5 (FSAA-LP), fed on FSAA (100%) and LP diet. The following parameters were measured during the treatment period: Plasma AA profiles including Phe and Tyr, growth, food and water intake and number of teeth cut. At the end of the treatment period, a body scan (fat and lean body mass) and a behavioral test (Barnes Maze) were performed. Finally, the brains were examined for content of Phe, Tyr, Trp, dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT) and 5-hydroxyindole-acetic acid (5-HIAA), and the bone density and bone mineral content were determined by dual-energy x-ray absorptiometry.

Results

Study 1: Mice off diet supplemented with CGMP (G1 (N-CGMP)) or supplemented with CGMP in combination with LNAA (G2 (N-CGMP-LNAA)) had significantly lower Phe in plasma and in the brain compared to mice fed only casein (G3 (N)). Extra LNAA (Tyr, Trp and Leu) to CGMP did not have any significant impact on Phe levels in the plasma and brain, but an increase in serotonin was measured in the brain of G2 mice compared to G1. Study 2: PKU mice fed with mixture of CGMP and EAA as supplement to LP diet (G4 (CGMP-EAA-LP)) demonstrated lower plasma-Phe levels but similar brain- Phe levels and growth as mice fed on an almost identical combination of FSAA (G5 (FSAA-LP)).

Conclusion

CGMP can be a relevant supplement for the treatment of PKU.

Engineering Organoids for in vitro Modeling of Phenylketonuria

Phenylketonuria is a recessive genetic disorder of amino-acid metabolism, where impaired phenylalanine hydroxylase function leads to the accumulation of neurotoxic phenylalanine levels in the brain. Severe cognitive and neuronal impairment are observed in untreated/late-diagnosed patients, and even early treated ones are not safe from life-long sequelae. Despite the wealth of knowledge acquired from available disease models, the chronic effect of Phenylketonuria in the brain is still poorly understood and the consequences to the aging brain remain an open question. Thus, there is the need for better predictive models, able to recapitulate specific mechanisms of this disease. Human induced pluripotent stem cells (hiPSCs), with their ability to differentiate and self-organize in multiple tissues, might provide a new exciting in vitro platform to model specific PKU-derived neuronal impairment. In this review, we gather what is known about the impact of phenylalanine in the brain of patients and highlight where hiPSC-derived organoids could contribute to the understanding of this disease.

Biotechnological Applications of Probiotics: A Multifarious Weapon to Disease and Metabolic Abnormality

Consumption of live microorganisms "Probiotics" for health benefits and well-being is increasing worldwide. Their use as a therapeutic approach to confer health benefits has fascinated humans for centuries; however, its conceptuality gradually evolved with methodological advancement, thereby improving our understanding of probiotics-host interaction. However, the emerging concern regarding safety aspects of live microbial is enhancing the interest in non-viable or microbial cell extracts, as they could reduce the risks of microbial translocation and infection. Due to technical limitations in the production and formulation of traditionally used probiotics, the scientific community has been focusing on discovering new microbes to be used as probiotics. In many scientific studies, probiotics have been shown as potential tools to treat metabolic disorders such as obesity, type-2 diabetes, non-alcoholic fatty liver disease, digestive disorders (e.g., acute and antibiotic-associated diarrhea), and allergic disorders (e.g., eczema) in infants. However, the mechanistic insight of strain-specific probiotic action is still unknown. In the present review, we analyzed the scientific state-of-the-art regarding the mechanisms of probiotic action, its physiological and immuno-modulation on the host, and new direction regarding the development of next-generation probiotics. We discuss the use of recently discovered genetic tools and their applications for engineering the probiotic bacteria for various applications including food, biomedical applications, and other health benefits. Finally, the review addresses the future development of biological techniques in combination with clinical and preclinical studies to explain the molecular mechanism of action, and discover an ideal multifunctional probiotic bacterium.

How does excess phenylalanine affect the packing density and fluidity of a lipid membrane?

Phenylketonuria (PKU) is an autosomal recessive error of phenylalanine (Phe) metabolism, where untreated Phe becomes cytotoxic. Previous experiments found that excess Phe decreases the packing density and increases the fluidity and permeability of a lipid membrane. It was proposed that Phe forms cytotoxic nanoscopic amyloid-like fibrils. In another study, the Phe fibrils were not visible near the lipid membrane. So, what leads to the deleterious effect of Phe on the lipid membrane? We put forward a molecular mechanism for the observed effect of excess Phe on the lipid membrane using all-atom molecular dynamics simulation. This study suggests that Phe monomers spontaneously intercalate into the membrane and form small hydrogen-bonded clusters, some of which locally perturb the membrane. These local effects result in an overall reduction in the membrane packing density, enhancement of membrane fluidity, and an increase of water permeability, observed in experiments. The present study does not observe any effect of the nanoscopic fibrillar structure of Phe on the membrane. This study, therefore, provides alternative insights into the excess Phe cytotoxicity in PKU disease.

Blood phenylalanine reduction reverses gene expression changes observed in a mouse model of phenylketonuria

Phenylketonuria (PKU) is a genetic deficiency of phenylalanine hydroxylase (PAH) in liver resulting in blood phenylalanine (Phe) elevation and neurotoxicity. A pegylated phenylalanine ammonia lyase (PEG-PAL) metabolizing Phe into cinnamic acid was recently approved as treatment for PKU patients. A potentially one-time rAAV-based delivery of PAH gene into liver to convert Phe into tyrosine (Tyr), a normal way of Phe metabolism, has now also entered the clinic. To understand differences between these two Phe lowering strategies, we evaluated PAH and PAL expression in livers of PAHenu2 mice on brain and liver functions. Both lowered brain Phe and increased neurotransmitter levels and corrected animal behavior. However, PAL delivery required dose optimization, did not elevate brain Tyr levels and resulted in an immune response. The effect of hyperphenylalanemia on liver functions in PKU mice was assessed by transcriptome and proteomic analyses. We observed an elevation in Cyp4a10/14 proteins involved in lipid metabolism and upregulation of genes involved in cholesterol biosynthesis. Majority of the gene expression changes were corrected by PAH and PAL delivery though the role of these changes in PKU pathology is currently unclear. Taken together, here we show that blood Phe lowering strategy using PAH or PAL corrects both brain pathology as well as previously unknown lipid metabolism associated pathway changes in liver.

Wearable wristband-based electrochemical sensor for the detection of phenylalanine in biofluids

Wearable electrochemical sensors are driven by the user-friendly capability of on-site detection of key biomarkers for health management. Despite the advances in biomolecule monitoring such as glucose, still, several unmet clinical challenges need to be addressed. For example, patients suffering from phenylketonuria (PKU) should be able to monitor their phenylalanine (PHE) level in a rapid, decentralized, and affordable manner to avoid high levels of PHE in the body which can lead to a profound and irreversible mental disability. Herein, we report a wearable wristband electrochemical sensor for the monitoring of PHE tackling the necessity of controlling PHE levels in PHE hydroxylase deficiency patients. The proposed electrochemical sensor is based on a screen-printed electrode (SPE) modified with a membrane consisting of Nafion, to avoid interferences in biofluids. The membrane also consists of sodium 1,2-naphthoquinone-4-sulphonate for the in situ derivatization of PHE into an electroactive product, allowing its electrochemical oxidation at the surface of the SPE in alkaline conditions. Importantly, the electrochemical sensor is integrated into a wristband configuration to enhance user interaction and engage the patient with PHE self-monitoring. Besides, a paper-based sampling strategy is designed to alkalinize the real sample without the need for sample pretreatment, and thus simplify the analytical process. Finally, the wearable device is tested for the determination of PHE in saliva and blood serum. The proposed wristband-based sensor is expected to impact the PKU self-monitoring, facilitating the daily lives of PKU patients toward optimal therapy and disease management.

Use of Exogenous Enzymes in Human Therapy: Approved Drugs and Potential Applications

The development of safe and efficacious enzyme-based human therapies has increased greatly in the last decades, thanks to remarkable advances in the understanding of the molecular mechanisms responsible for different diseases, and the characterization of the catalytic activity of relevant exogenous enzymes that may play a remedial effect in the treatment of such pathologies. Several enzyme-based biotherapeutics have been approved by FDA (the U.S. Food and Drug Administration) and EMA (the European Medicines Agency) and many are undergoing clinical trials. Apart from enzyme replacement therapy in human genetic diseases, which is not discussed in this review, approved enzymes for human therapy find applications in several fields, from cancer therapy to thrombolysis and the treatment, e.g., of clotting disorders, cystic fibrosis, lactose intolerance and collagen-based disorders. The majority of therapeutic enzymes are of microbial origin, the most convenient source due to fast, simple and cost-effective production and manipulation. The use of microbial recombinant enzymes has broadened prospects for human therapy but some hurdles such as high immunogenicity, protein instability, short half-life and low substrate affinity, still need to be tackled. Alternative sources of enzymes, with reduced side effects and improved activity, as well as genetic modification of the enzymes and novel delivery systems are constantly searched. Chemical modification strategies, targeted- and/or nanocarrier-mediated delivery, directed evolution and site-specific mutagenesis, fusion proteins generated by genetic manipulation are the most explored tools to reduce toxicity and improve bioavailability and cellular targeting. This review provides a description of exogenous enzymes that are presently employed for the therapeutic management of human diseases with their current FDA/EMA-approved status, along with those already experimented at the clinical level and potential promising candidates.

In silico screening and molecular dynamics simulation of deleterious PAH mutations responsible for phenylketonuria genetic disorder

Phenylketonuria (PKU) is a genetic disorder that if left untreated can lead to behavioral problems, epilepsy, and even mental retardation. PKU results from mutations within the phenylalanine-4-hydroxylase (PAH) gene that encodes for the PAH protein. The study of all PAH causing mutations is improbable using experimental techniques. In this study, a collection of in silico resources, sorting intolerant from tolerant, Polyphen-2, PhD-SNP, and MutPred were used to identify possible pathogenetic and deleterious PAH non-synonymous single nucleotide polymorphisms (nsSNPs). We identified two variants of PAH, I65N and L311P, to be the most deleterious and disease causing nsSNPs. Molecular dynamics (MD) simulations were carried out to characterize these point mutations on the atomic level. MD simulations revealed increased flexibility and a decrease in the hydrogen bond network for both mutants compared to the native protein. Free energy calculations using the MM/GBSA approach found that BH4 , a drug-based therapy for PKU patients, had a higher binding affinity for I65N and L311P mutants compared to the wildtype protein. We also identify important residues in the BH4 binding pocket that may be of interest for the rational drug design of other PAH drug-based therapies. Lastly, free energy calculations also determined that the I65N mutation may impair the dimerization of the N-terminal regulatory domain of PAH.

Neonatal screening and genotype-phenotype correlation of hyperphenylalaninemia in the Chinese population

Background

Hyperphenylalaninemia (HPA) is the most common amino acid metabolic disease involving phenylalanine hydroxylase (PAH, OMIM*612,349) deficiency or coenzyme tetrahydrobiopterin (BH4) deficiency. Patients with severe HPA often have a difficult life. Early diagnosis of HPA before the development of symptoms is possible via neonatal screening, facilitating appropriate treatment and reducing mortality and disability rates. This study revealed the prevalence, mutational and phenotypic spectrum, and prognosis of HPA by neonatal screening from January 2001 to September 2020 in Nanjing, Jiangsu Province, China.

Methods

Through a retrospective analysis of the information available in the neonatal screening database, the clinical presentations, laboratory data, molecular characteristics and treatment follow-up data of HPA patients detected by neonatal screening were evaluated.

Results

We diagnosed 181 patients with HPA from 1 to 957 newborns, giving an incidence of 1:6873. Among these patients, 177 were identified as PAH deficient and four patients were BH4 deficient. The average current age of the patients was 6.38 years old. The most common mutations of PAH were c.728 C > A/ p.Arg243Gln (13.83 %), c.158G > A/ p.Arg53His (9.57 %), c.611 A > G/ p.Tyr204Cys (7.44 %), and c.721 C > T/ p.Arg241Cys (6.38 %).

Conclusions

This study revealed the prevalence, phenotype-genotype, and prognosis of HPA in China and contributes to the updating of PAHD data for China and worldwide. Our study not only expanded the spectrum of phenotypes and genotype but also provided a valuable tool for improved genetic counseling and management of future cases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01846-w.

Long-Term Neurological Outcomes of Adult Patients with Phenylketonuria before and after Newborn Screening in Japan

Japanese newborn screening (NBS) for phenylketonuria (PKU) was initiated in 1977. We surveyed the neurological outcomes of Japanese adult patients with PKU to investigate the long-term effects and of and issues with NBS. Eighty-five patients with PKU aged over 19 years who continued to be treated with a phenylalanine-free amino acid formula were investigated by administering questionnaires regarding clinical characteristics, such as mental ability, education status, and therapeutic condition. Of the 85 subjects, 68 patients were detected by NBS (NBS group), while the other 17 were clinically diagnosed before the initiation of NBS (pre-NBS group). Further, 10 of the 68 NBS patients presented intellectual and/or psychiatric disabilities, 5 of whom had a history of treatment discontinuation; in contrast, 12 of the 17 pre-NBS patients presented with neuropsychiatric symptoms. Regarding social outcomes, almost all patients in the NBS group could live an independent life, while over half of the patients in the pre-NBS group were not employed or lived in nursing-care facilities. Neurological outcomes are obviously improved by NBS in Japan. However, some patients, even those detected by NBS, developed neuropsychiatric symptoms due to treatment disruption. Lifelong and strict management is essential to maintain good neurological and social prognoses for patients with PKU.

Investigating the basis for the antidepressant effects of Gleditsiae spina using an integrated metabolomic strategy

OBJECTIVES

Gleditsiae spina (GS) is a natural antidepressant but its mechanisms of action remain unclear. In the present study, taxifolin (Tax) was selected to determine the role of flavonoids in the antidepressant effects of GS.

MATERIALS AND METHODS

Urine samples from C57BL/6 mice were analyzed based on ultra performance liquid chromatography-quadrupole time of flight mass spectrometry (UPLC-Q/TOF-MS). Then, we investigated the therapeutic effects of GS and Tax in depression models in vivo. An integrated metabolomic approach was used to examine the metabolic profiles of GS/Tax groups and corticosterone model groups (Cor). Metabolic networks in response to GS/Tax treatment were established for the comparison of antidepressant activities.

RESULTS

Corticosterone exposure significantly increased serum levels of corticosterone but decreased serum levels of 5-hydroxytryptamine and sucrose consumption (P<0.01). Treatment with GS and Tax improved all measured variables compared to those of the corticosterone-exposed group (P< 0.01). The antidepressant effects of GS and Tax involved the regulation of pentose and glucuronate interconversions, arginine and proline metabolism, phenylalanine metabolism, taurine and hypotaurine metabolism, and the citrate cycle.

CONCLUSION

These findings indicate that flavonoids form the pharmacodynamic basis of the antidepressant effects of GS. Moreover, our findings highlight that integrated metabolomics provides a powerful tool to study the mechanisms and material basis of Chinese herbs.

Compound Sophorae Decoction: treating ulcerative colitis by affecting multiple metabolic pathways

Ulcerative colitis (UC) is a chronic refractory non-specific intestinal inflammatory disease that is difficult to be cured. The discovery of new ulcerative colitis-related metabolite biomarkers may help further understand UC and facilitate early diagnosis. It may also provide a basis for explaining the mechanism of drug action in the treatment of UC. Compound Sophorae Decoction (CSD) is an empirical formula used in the clinical treatment of UC. Although it is known to be efficacious, its mechanism of action in the treatment of UC is unclear. The purpose of this study was to investigate the changes in endogenous substances in UC rats and the effects of CSD on metabolic pathways using the metabonomics approach. Metabolomics studies in rats with UC and normal rats were performed using LC-MS/MS. Rats with UC induced using TNBS enema were used as the study models. Metabolic profiling and pathway analysis of biomarkers was performed using statistical and pathway enrichment analyses. 36 screened potential biomarkers were found to be significantly different between the UC and the normal groups; it was also found that CSD could modulate the levels of these potential biomarkers. CSD was found to be efficacious in UC by regulating multiple metabolic pathways.

Protein Substitute Requirements of Patients with Phenylketonuria on BH4 Treatment: A Systematic Review and Meta-Analysis

The traditional treatment for phenylketonuria (PKU) is a phenylalanine (Phe)-restricted diet, supplemented with a Phe-free/low-Phe protein substitute. Pharmaceutical treatment with synthetic tetrahydrobiopterin (BH4), an enzyme cofactor, allows a patient subgroup to relax their diet. However, dietary protocols guiding the adjustments of protein equivalent intake from protein substitute with BH4 treatment are lacking. We systematically reviewed protein substitute usage with long-term BH4 therapy. Electronic databases were searched for articles published between January 2000 and March 2020. Eighteen studies (306 PKU patients) were eligible. Meta-analyses demonstrated a significant increase in Phe and natural protein intakes and a significant decrease in protein equivalent intake from protein substitute with cofactor therapy. Protein substitute could be discontinued in 51% of responsive patients, but was still required in 49%, despite improvement in Phe tolerance. Normal growth was maintained, but micronutrient deficiency was observed with BH4 treatment. A systematic protocol to increase natural protein intake while reducing protein substitute dose should be followed to ensure protein and micronutrient requirements are met and sustained. We propose recommendations to guide healthcare professionals when adjusting dietary prescriptions of PKU patients on BH4. Studies investigating new therapeutic options in PKU should systematically collect data on protein substitute and natural protein intakes, as well as other nutritional factors.

Molecular characterization of Thai patients with phenylalanine hydroxylase deficiency and in vitro functional study of two novel PAH variants

Phenylketonuria (PKU) is an autosomal recessive amino acid metabolism disorder caused by variants in the gene encoding phenylalanine hydroxylase (PAH; EC1.14.16.1). This study aimed to assess the specific heterogeneity of PAH variants found in Thai population as well as evaluate enzyme activity and expression of novel variants. PAH gene from 13 patients was analyzed by PCR amplification and direct Sanger-sequencing of 13 exons of the coding region. The novel variants were transiently transfected in COS-7 cells for functional verification. Eleven different PAH variants were identified: all pathogenic variants were missense variants, of which the most frequent variant was p.R169L, accounting for 24% (6/25) of all identified alleles. Two novel variants p.R169L and p.Y317N and previously reported variants with mutated residues at the same positions (p.R169H and p.Y317H) were expressed in COS-7 cells. These showed mildly impaired residual activity levels (42.3-63.1% of wild type), while the protein levels were well expressed (82.8-110%), except for p.R169L, which showed decreased protein expression of 55.7% compared to the wild type enzyme. All subjects with p.R169L identified in at least one of pathogenic alleles (one case is homozygous) had a metabolic phenotype of mild hyperphenylalaninemia (HPA). Our data has expanded the information on the genetic heterogeneity of Thai patients with PAH deficiency. This finding emphasizes the importance of genotyping in patients with HPA, and in vitro studies can provide additional information for prediction of phenotype.

Insights from Animal Models on the Pathophysiology of Hyperphenylalaninemia: Role of Mitochondrial Dysfunction, Oxidative Stress and Inflammation

Phenylketonuria (PKU) is an inborn error of metabolism caused by phenylalanine hydroxylase (PAH) deficiency and characterized by elevated plasma levels of phenylalanine (hyperphenylalaninemia-HPA). In severe cases, PKU patients present with neurological dysfunction and hepatic damage, but the underlying mechanisms are not fully elucidated. Other forms of HPA also characterized by neurological symptoms occur in rare instances due to defects in the metabolism of the PAH cofactor tetrahydrobiopterin. This review aims to gather the knowledge acquired on the phenylalanine-induced toxicity focusing on findings obtained from pre-clinical studies. Mounting evidence obtained from PKU genetic mice, rats submitted to different HPA models, and cell cultures exposed to phenylalanine has shown that high levels of this amino acid impair mitochondrial bioenergetics, provoke changes in oxidative and inflammatory status, and induce apoptosis. Noteworthy, some data demonstrated that phenylalanine-induced oxidative stress occurs specifically in mitochondria. Further studies have shown that the metabolites derived from phenylalanine, namely phenylpyruvate, phenyllactate, and phenylacetate, also disturb oxidative status. Therefore, it may be presumed that mitochondrial damage is one of the most important mechanisms responsible for phenylalanine toxicity. It is expected that the findings reviewed here may contribute to the understanding of PKU and HPA pathophysiology and to the development of novel therapeutic strategies for these disorders.

In vivo cytidine base editing of hepatocytes without detectable off-target mutations in RNA and DNA

Base editors are RNA-programmable deaminases that enable precise single-base conversions in genomic DNA. However, off-target activity is a concern in the potential use of base editors to treat genetic diseases. Here, we report unbiased analyses of transcriptome-wide and genome-wide off-target modifications effected by cytidine base editors in the liver of mice with phenylketonuria. The intravenous delivery of intein-split cytidine base editors by dual adeno-associated viruses led to the repair of the disease-causing mutation without generating off-target mutations in the RNA and DNA of the hepatocytes. Moreover, the transient expression of a cytidine base editor mRNA and a relevant single-guide RNA intravenously delivered by lipid nanoparticles led to ~21% on-target editing and to the reversal of the disease phenotype; there were also no detectable transcriptome-wide and genome-wide off-target edits. Our findings support the feasibility of therapeutic cytidine base editing to treat genetic liver diseases.

Continuation of pegvaliase treatment during pregnancy: A case report

Phenylalanine hydroxylase (PAH) deficiency is an inborn error of phenylalanine (Phe) metabolism that results in the buildup of dietary Phe to potentially toxic levels. Poorly controlled Phe levels in women of childbearing age are particularly worrisome due to the toxic effect of elevated Phe on fetal development. Pegvaliase was recently approved as an enzyme substitution therapy to reduce Phe concentrations in adult patients with PAH deficiency who have suboptimal Phe control on existing management. During the pegvaliase clinical trials pregnant patients were excluded from participation, but the approved label does not contraindicate its use during pregnancy. This case report describes the outcome of the first PAH deficient patient who elected to continue treatment with pegvaliase during pregnancy and reviews the lessons learned and future considerations.