Phenylketonuria Dietary Management and an Emerging Development

Diet therapy in patients with rare diseases: a scoping review

BACKGROUND

This scoping review presents existing research evidence regarding diet therapy in patients with rare diseases (RDs).

METHODS

Using the five-stage scoping review framework proposed by Arksey, O'Malley and Levac, we searched the published literature in PubMed, Web of Science, Royal Society of Chemistry, China National Knowledge Infrastructure, VIP Database and Wan Fang Database from January 2010 to November 2022. We selected diet therapy studies on 121 RDs, as categorised by the National Health Commission of China in 2018. Charts for research analysis were developed and used to categorise the data.

RESULTS

We ultimately included 34 diet therapy studies from 19 countries and territories for 10 RDs and 3 RD groups. RD diet therapy studies have mainly focused on inborn errors of metabolism (92.3%) and are common in Western countries. Most studies focused on diet therapy methods for RDs (44%). In addition, 29% of studies included diet therapy management, 15% included guidelines for diet therapy and 12% included the impact of diet therapy on patients.

CONCLUSIONS

Current diet therapies for RDs lack specificity and present with limited characteristics. Therefore, it is necessary to expand the scope and depth of future research and explore evidence-based recommendations and new diet therapies focused on patient needs and family support to provide a reference for improving the efficacy and safety of diet therapies for RDs.

The phenylketonuria patient: A recent dietetic therapeutic approach

Phenylalanine hydroxylase (PAH) deficiency, commonly named phenylketonuria (PKU) is a disorder of phenylalanine (Phe) metabolism inherited with an autosomal recessive trait. It is characterized by high blood and cerebral Phe levels, resulting in intellectual disabilities, seizures, etc. Early diagnosis and treatment of the patients prevent major neuro-cognitive deficits. Treatment consists of a lifelong restriction of Phe intake, combined with the supplementation of special medical foods, such as Amino Acid medical food (AA-mf), enriched in tyrosine (Tyr) and other amino acids and nutrients to avoid nutritional deficits. Developmental and neurocognitive outcomes for patients, however, remain suboptimal, especially when adherence to the demanding diet is poor. Additions to treatment include new, more palatable foods, based on Glycomacropeptide that contains limited amounts of Phe, the administration of large neutral amino acids to prevent phenylalanine entry into the brain and tetrahydrobiopterin cofactor capable of increasing residual PAH activity. Moreover, further efforts are underway to develop an oral therapy containing phenylalanine ammonia-lyase. Nutritional support of PKU future mothers (maternal PKU) is also discussed. This review aims to summarize the current literature on new PKU treatment strategies.

The beneficial effect of psychological support on mothers with PKU children who suffer from social discrimination and damage of quality of life

Background Phenylketonuria (PKU) is a metabolic disorder of phenylalanine (phe) metabolism caused by the liver enzyme phe hydroxylase deficiency resulting in mental retardation. The only treatment for this disorder is the lifelong restriction of natural protein supplemented with phe-free amino acid formula. The aim of this study was to demonstrate the beneficial effect of psychological support in relation to the educational status on mothers with PKU children, who suffered from social discrimination (SD) and damage of quality of life (QLD). Methods A total number of 42 mothers with PKU children with a mean age of 26.8 years took part in this study. According to their educational status, they were divided into three groups: group a, primary school (n = 13); group b, high school (n = 15) and group c, university degree (n = 14). Psychological support was given once per week for 1 year. Results University degree mothers achieved the best results in ameliorating their symptoms and signs. Mothers who had completed high school felt a moderate amelioration of their SD and QL, whereas those who had finished primary school only felt a mild reduction of their symptoms. Educational status of the affected mothers should be always taken into account for the classification of the affected mothers into therapeutic groups. Familial and professional environment are very important for the success of psychological support. Conclusions Overall, the psychological support related to symptoms and signs of this metabolic disorder is in comparison with that in diabetic patients.

In vitro residual activities in 20 variants of phenylalanine hydroxylase and genotype-phenotype correlation in phenylketonuria patients

Phenylketonuria (PKU), caused by phenylalanine hydroxylase (PAH) gene variants, is a common autosomal inherited metabolic disease. So far, 1111 PAH variants have been revealed. The residual activity of the PAH variants is the key determinant of the metabolic phenotype and BH₄ responsiveness in PKU patients. In this study, the spectrum of PAH variants in 1083 Chinese PKU patients was analyzed. Then 20 variants (p.L52F, p.R86P, p.L128P, p.L142P, p.D163N, p.C203G, p.E214G, p.F260L, p.M276T, p.L311R, p.P314A, p.L364F, p.Q375H, p.F382I, p.A395S, p.V412D, p.E108*, p.C203*, p.C284* and p.E353*) were expressed in COS-7 cells. The residual activities and protein expression levels were detected by isotope-dilution liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) and Western blotting, respectively. We compared the results of the phenotypic prediction based on APV and PAH activity respectively, and further explored the relationship between residual activity and phenotype in PKU patients. We reported 9 newly discovered PAH variants for the first time, thereby expanding the spectrum of PAH variants. Among the 20 variants in our assay, 8 variants showed mild impaired residual activities (48-92%) and approximately normal protein expression levels compared to the wild-type PAH. In contrast, 9 variants showed severely impaired residual activities (0-34%) and reduced protein expression. However, three variants (p.L52F, p.F260L and p.P314A) showed impaired residual activities (5%, 32% and 29%), although the proteins were well expressed. We assigned APV scores for 14 variants, in which the results of the phenotypic prediction were consistent for 12/14 (86%) variants based on APV and residual activity respectively, and the residual activity correctly predicted 17/22 (77%) of the patients. Our study helped to further understand the genotype-phenotype correlation in PKU patients.

The significant role of educational status in PKU patients: the beneficial effect of psychological support in depression

INTRODUCTION

Classical Phenylketonuria (PKU) is a metabolic disease characterized by high phenylalanine (phe) levels in blood and brain. PKU patients are commonly treated with low phe diet supplemented with amino acid free formula. High Phe levels minimize brain tryptophan concentration, the pressure of serotonin, which is responsible for the appearance of depression symptoms. Both amino acids share the same pathway for entering CNS via BBB. Aimed to determine the effect of psychological support on different education status depressed PKU patients via adherence to their diet.

METHODS

PKU patients (n = 110) were divided into groups according to their education status: Primary school, High school, University degree. All patients were tasted with a Patient Health Questionnaire (PHQ-9) standardized for Greek population. Psychological support was performed in every depressed patient ones per two weeks for three successive months under the same conditions. Phe blood levels were measured before psychological support and every 15-20 days till the end of the study.

RESULTS

Only 2/110 (1.8%) participance had finished Primary school and were healthy. 72/110 (65.5%) High School, out of them 29 were depressed and 36/110 (32.7%) achieved a University degree, only 6 suffered from depression. High phe blood levels were measured in the depressed patients, which dropped near to normal after the end of their psychological support. Referring to depression symptoms, all participance except one presented amelioration of their mood.

CONCLUSIONS

Psychological support is beneficial on depressed PKU patients graduated with High School or University degree via adherence to their special diet.

The significant role of amino acids during pregnancy: nutritional support

Background: Pregnancy is characterized by a complexity of metabolic processes that may impact fetal development and infant health outcome. Normal fetal growth and development depend on a continuous supply of nutrients via the placenta. The placenta transports, utilizes, produces, and interconverts amino acids (AAs).Findings: Concentrations of both nonessential and essential AAs in maternal plasma decrease in early pregnancy and persist at low concentrations throughout. The decline is greatest for the glucogenic AAs and AAs of the urea cycle. Additionally, there is a large placental utilization of the branched-chain AAs, some of which are transaminated to alpha ketoacids and contribute to placental ammonia production. Both nonessential and essential AAs regulate key metabolic pathways to improve health, survival, growth, development, lactation, and reproduction of organisms. Some of the nonessential AAs (e.g. glutamine, glutamate, and arginine) play also important roles in regulating gene expression, cell signaling, antioxidant responses, immunity, and neurological function.Conclusions: Nutritional support during pregnancy is of great interest focusing not only to common pregnancies but also to those with low socioeconomic status, vegan-vegetarian groups, and pregnant women with metabolic disorders, the most known maternal phenylketonuria. The latter is of great interest because phenylalanine must be within the recommended range throughout pregnancy in addition to other nutrients such as vitamin B12, folate, etc. Loss of the adherence to this specific diet results in congenital malformations of the fetus. In addition to the routine laboratory test, quantitation of plasma AAs may be necessary throughout pregnancy.