The Prevalence of Phenylketonuria in Arab Countries, Turkey, and Iran: A Systematic Review

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.

Genotypic variants of the tetrahydrobiopterin (BH4) biosynthesis genes in patients with hyperphenylalaninemia from different regions of Iran

BACKGROUND

Hyperphenylalaninemia (HPA) is a metabolic disorder classified into phenylalanine-4-hydroxylase (PAH) and non-PAH deficiency. The latter is produced by mutations in genes involved in the tetrahydrobiopterin (BH4) biosynthesis pathway and DNAJC12 pathogenetic variants. The BH4 metabolism, including de novo biosynthesis involved genes (i.e., guanosine 5'-triphosphate cyclohydrolase I (GTPCH/GCH1), sepiapterin reductase (SR/SPR), 6-pyruvoyl-tetrahydropterin synthase (PTPS/PTS)), and two genes that play roles in cofactor regeneration pathway (i.e., dihydropteridine reductase (DHPR/QDPR) and pterin-4α-carbinolamine dehydratase (PCD/PCBD1)). The subsequent systemic hyperphenylalaninemia and monoamine neurotransmitter deficiency lead to neurological consequences. The high rate of consanguineous marriages in Iran substantially increases the incidence of BH4 deficiency.

METHODS

We utilized the Sanger sequencing technique in this study to investigate 14 Iranian patients with non-PAH deficiency. All affected subjects in this study had HPA and no mutation was detected in their PAH gene.

RESULTS

We successfully identified six mutant alleles in BH4-deficiency-associated genes, including three novel mutations: one in QDPR, one in PTS, and one in the PCBD1 gene, thus giving a definite diagnosis to these patients.

CONCLUSION

In this light, appropriate patient management may follow. The clinical effect of reported variants is essential for genetic counseling and prenatal diagnosis in the patients' families and significant for the improvement of precision medicine.

Life story of Iranian parents of a child with phenylketonuria: a qualitative study

Parents of a child with phenylketonuria (PKU) face many challenges in childcare. It is crucial for health care workers to understand the situation of parents of a child with PKU and their needs. The purpose of this study was to explore the life story of parents with a child with PKU. This qualitative study has been done with a conventional content analysis approach. Twenty-four parents were selected purposefully. A semi-structured interview was conducted. Data analysis identified three main themes, which included parental reactions, consequences of a child with PKU in parents, and parents' needs. Parents of children with PKU can be considered people at risk for mental health because of their feelings of isolation and their lonely struggle to manage the disease and its effects on their child. This study shows that mothers need more support due to the misconceptions in and attitudes of their social environment. Therefore, it is necessary to understand this group, their needs and lives, and provide further support and promote empathy in the health system for the parents.

Identification of Variants Underlying Phenylalanine Hydroxylase Deficiency in Saudi Arabia

Background: Deleterious mutations in the human gene phenylalanine hydroxylase (PAH) encoding the phenylalanine hydroxylase enzyme give rise to classic phenylketonuria and hyperphenylalaninemia. Our study was designed to characterize the spectrum of variants in the PAH gene in Saudi patients. Materials and Methods: We screened a cohort of 72 Saudi patients with clinical and biochemical diagnoses of hyperphenylalaninemia at the largest tertiary care center in Saudi Arabia; the King Faisal Specialist Hospital and Research Center (KFSH&RC), Riyadh. All patient's charts were reviewed under an approved study by Institutional Review Board. Results: Twenty-one different PAH variants were identified among the 144 PAH alleles assessed by targeted gene sequencing. Within the studied cohort, 60 of 72 patients had homozygous mutations with the the remaining 12 being compound heterozygotes. The most prevalent of the disease alleles identified in this study was the p.(Arg252Trp) mutation, which accounted for 38 of 144 alleles (26.4%). With the high incidence of genetic disorders in the population, religiously permissible preventive reproductive measures are a priority in our practice. Prenatal diagnoses carried out on four fetuses revealed two that were homozygous for PAH pathogenic variants. In addition, pre-implantation genetic diagnoses were initiated for 19 families. Eight of these families completed more than one full cycle of treatment, from which one healthy newborn was delivered. Conclusions: This study describes the spectrum of PAH variants in the Saudi population and highlights the molecular heterogeneity underlying phenylketonuria and hyperphenylalaninemia. These results add to the existing knowledge about PAH variants in Middle Eastern Countries. These results can be further translated to provide: informed counseling; cascade carrier testing in extended family members; and pre-marital screening.

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.

An update of the mutation spectrum of phenylalanine hydroxylase (PAH) gene in the population of Turkey

Phenylketonuria (PKU) is an autosomal recessive disorder of phenylalanine metabolism, mostly caused by PAH gene variants. The aim of this study was to identify the frequency of PAH gene variants in Turkish population with PKU. In 433 patients with PKU, PAH gene was examined using next generation sequencing (NGS) method. IVS10- 11G>A, p.R261Q, p.A300S, p.A403V, and p.T380 variants, which are the most common variants in this study, constituted 45,9% of the variants in our study. Nine novel variants p.A34V, K73Qfs*4, R157H, R261S, p.T266I, p.S310P, T328A, p.F351I, and K363N were identified. This study determines the most common PAH variants in Turkey and shows that PKU can be screened before marriage with the screening kits. Identification of the PAH gene variant spectrum is important for early diagnosis, understanding molecular mechanisms, clinical follow-up, treatment, and genetic counseling. And the novel variants found this study are important for further studies.

Epidemiology of Phenylketonuria Disease in Jordan: Medical and Nutritional Challenges

Background: Phenylketonuria (PKU) is the most frequent inborn error in amino acid metabolism caused by a deficiency of the phenylalanine hydroxylase enzyme (PAH). If PKU is left untreated, high concentrations of phenylalanine (Phe) accumulate in the blood, leading to severe brain dysfunction, neurodevelopmental, behavioral and psychological problems. Data concerning the epidemiology of PKU in Jordan are limited. The main objectives of our study were to determine the prevalence of PKU in Jordan, analyze the PKU phenotypes, and identify major challenges in providing dietary management to PKU patients. Methods: Data were collected utilizing the medical records of PKU patients attending the PKU clinic at the Ministry of Health in Amman, Jordan, between 2008 and 2021. Results: The total number of patients diagnosed with PKU was 294. The prevalence of PKU was estimated to be 1/5263. Most patients were Jordanians (90.8%), and 9.2% were non-Jordanians. More than half of the patients (56%) were diagnosed through the national newborn screening (NBS) program. Regarding the phenotypes of PKU, 46.6% had moderate PKU, whereas 42.9% had the classic type of PKU and only 8 (2.7%) had cofactor Tetrahydrobiopterin (BH4) deficiency (atypical PKU). According to the age of diagnosis, 66% of patients were diagnosed more than 30 days post-birth. Consanguinity was found in 87.4% of patients, and the majority of patients, 218 (74.2%), had first-degree consanguinity. The most common complication was mental retardation (31%). Most patients were committed to dietary management (83%) and developed fewer complications. Conclusion: In our study, we demonstrated the importance of the NBS program in the early identification and diagnosis of new PKU cases which allows the initiation of treatment and dietary management to prevent severe complications of PKU in Jordan.

Health Related Quality of Life of Caregivers of Children and Adolescents With Phenylketonuria: A Systematic Review

Introduction. Caregivers of children with chronic illness are at risk of having impairment in their quality of life (QOL). We systematically reviewed the available literature related to the Health Related Quality Of Life (HRQOL) of caregivers of children with Phenylketonuria (PKU). Methods. We comprehensively searched in electronic databases including Scopus, Science Direct, CINAHL, Medline, PubMed, Google scholar, and ProQuest. The search criteria included studies with samples more than one, children suffering from PKU, exploring parents or primary caregiver’s HRQOL, published from 2010 to 2020, full article available for download and published in English. Eight studies including 5 cross sectional studies, 1 open label trial, and 2 surveys were systematically reviewed. Results. Seven out of 8 studies have established a negative correlation between PKU and parent’s HRQOL in at least 1 of the domains. In one study, the HRQOL of parents is higher than their population norms. Conclusion. Most of the caregivers had poor to moderate HRQOL. More studies are required to explore HRQOL of caregivers of children with PKU using similar tools and outcome measures addressing all the domains of HRQOL in order to have more clarity on the impact of PKU on caregiver’s HRQOL. Interventional studies might help in improving the HRQOL of caregivers.

A joint method for the screening of pharmacological chaperones for phenylalanine hydroxylase

Phenylalanine hydroxylase (PAH) deficiency (PAHD) is an autosomal recessive disorder that causes severe injury to the nervous system, the treatment of which mainly depends on dietary therapy. The limited treatment options for PAHD are an incentive to develop new methods to identify more efficient therapeutic drugs, such as agonists which could improve PAH activity. In this study, we aimed to establish a rapid and convenient method for the screening and verification of PAH agonists. We compared fluorospectrophotometry and tandem mass spectrometry for detection of enzymatic formation of tyrosine, finding that the latter was a more sensitive method. We optimized immunoprecipitation purification conditions and measurement conditions of PAH activity. The optimal ratio between PAH protein and magnetic beads was 500 μg protein per 20 μL beads, and the optimized conditions for the detection of PAH enzymatic activity included the presence of 75 μM coenzyme ((6R)-l-erythro-5,6,7,8-tetrahydrobiopterin) and 30 min reaction time. Based on virtual screening, we screened ten candidate agonists from the FDA drug library. Three of these (nefopam, fluocinonide, and risperidone) were found to activate the enzyme in a dose-dependent manner (0.1-10 μM) by the joint method. We tested the efficacy of the three agonists on three PAH mutations (p.I65T, p.H107R, and p.D101N) that influence enzyme activity, and found that risperidone could specifically activate D101N-mutated enzyme. In conclusion, we established a joint method that is highly reliable, cost-effective, labor-saving, and time-saving. And we also found a specific agonist for D101N-mutated PAH by this joint method which may assist the development of clinical treatment for PAHD patients with different enzyme deficiencies.

A policy analysis of the national phenylketonuria screening program in Iran

Background

Phenylketonuria (PKU) screening is a public health measure taken to diagnose and treat the patients with PKU to prevent severe neurological disorders in them. The present study was aimed at analyzing the policies of the national PKU screening (NaPS) program in Iran.

Methods

PKU screening program policies were analyzed in compliance with the policy triangle model. Document review and 38 semi-structured interviews were used for data collection. Document review data were analyzed using content analysis, and interview data were analyzed using framework analysis.

Results

The national PKU screening (NaPS) program was a decision made at the genetics department of Ministry of Health and Medical Education (MOHME) in Iran. Many internal and external stakeholders were involved in it and valid evidence was used to formulate the policies. Despite some opposition and insufficient support, the program was implemented due to the continuous persistence of parents, interested executives, formulated valid content and a top-down approach. The main barriers included rapid substitution of managers, shortage of Phe-free milk, little awareness of patients’ families, social stigma, and inadequate co-operation of some hospital administrators.

Conclusions

The policy triangle framework contributed to explaining the different components of the PKU screening program. A successful PKU screening program requires more stability of senior managers in MOHME, enough human resources and Phe-free milk, educating patients’ families, and commitment of hospitals administrators. Meanwhile, all the stakeholders need to be involved in the program effectively.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12913-021-06116-w.

Phenylketonuria in Portugal: Genotype-phenotype correlations using molecular, biochemical, and haplotypic analyses

Background

The impairment of the hepatic enzyme phenylalanine hydroxylase (PAH) causes elevation of phenylalanine levels in blood and other body fluids resulting in the most common inborn error of amino acid metabolism (phenylketonuria). Persistently high levels of phenylalanine lead to irreversible damage to the nervous system. Therefore, early diagnosis of the affected individuals is important, as it can prevent clinical manifestations of the disease.

Methods

In this report, the biochemical and genetic findings performed in 223 patients diagnosed through the Portuguese Neonatal Screening Program (PNSP) are presented.

Results

Overall, the results show that a high overlap exists between different types of variants and phenylalanine levels. Molecular analyses reveal a wide mutational spectrum in our population with a total of 56 previously reported variants, most of them found in compound heterozygosity (74% of the patients). Intragenic polymorphic markers were used to assess the haplotypic structure of mutated chromosomes for the most frequent variants found in homozygosity in our population (p.Ile65Thr, p.Arg158Gln, p.Leu249Phe, p.Arg261Gln, p.Val388Met, and c.1066‐11G>A).

Conclusion

Our data reveal high heterogeneity at the biochemical and molecular levels and are expected to provide a better understanding of the molecular basis of this disease and to provide clues to elucidate genotype–phenotype correlations.

Molecular genetics of phenylketonuria and tetrahydrobiopterin deficiency in Jordan

BACKGROUND

Information regarding the prevalence of PKU in the Middle East in comparison to other world regions is scarce, which might be explained by difficulties in the implementation of national newborn screening programs.

OBJECTIVE

This study seeks for the first time to genotype and biochemically characterize patients diagnosed with hyperphenylalaninemia (HPA) at the Pediatric Metabolic Genetics Clinic at the King Hussein Medical Center, Amman, Jordan.

METHODS

A total of 33 patients with HPA and 55 family members were investigated for pterins (neopterin and biopterin) and dihydropteridine reductase (DHPR) activity in dried blood spots. Patients with HPA were genotyped for phenylketonuria (PKU) and the genes involved in tetrahydrobiopterin (BH4) metabolism.

RESULTS

In total 20 patients were diagnosed with PKU due to phenylalanine hydroxylase (PAH) deficiency, 2 with GTP cyclohydrolase I (GTPCH) deficiency, 6 with DHPR deficiency, and 3 with the 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. Diagnosis was not possible in 2 patients. This study documents a high percentage of BH4 deficiencies within HPA patients. With one exception, all patients were homozygous for particular gene variants.

CONCLUSIONS

This approach enables differentiation between PKU and BH4 deficiencies and, thus, allows for critical selection of a specific treatment strategies.

The Genetic Landscape and Epidemiology of Phenylketonuria

Phenylketonuria (PKU), caused by variants in the phenylalanine hydroxylase (PAH) gene, is the most common autosomal-recessive Mendelian phenotype of amino acid metabolism. We estimated that globally 0.45 million individuals have PKU, with global prevalence 1:23,930 live births (range 1:4,500 [Italy]-1:125,000 [Japan]). Comparing genotypes and metabolic phenotypes from 16,092 affected subjects revealed differences in disease severity in 51 countries from 17 world regions, with the global phenotype distribution of 62% classic PKU, 22% mild PKU, and 16% mild hyperphenylalaninemia. A gradient in genotype and phenotype distribution exists across Europe, from classic PKU in the east to mild PKU in the southwest and mild hyperphenylalaninemia in the south. The c.1241A>G (p.Tyr414Cys)-associated genotype can be traced from Northern to Western Europe, from Sweden via Norway, to Denmark, to the Netherlands. The frequency of classic PKU increases from Europe (56%) via Middle East (71%) to Australia (80%). Of 758 PAH variants, c.1222C>T (p.Arg408Trp) (22.2%), c.1066-11G>A (IVS10-11G>A) (6.4%), and c.782G>A (p.Arg261Gln) (5.5%) were most common and responsible for two prevalent genotypes: p.[Arg408Trp];[Arg408Trp] (11.4%) and c.[1066-11G>A];[1066-11G>A] (2.6%). Most genotypes (73%) were compound heterozygous, 27% were homozygous, and 55% of 3,659 different genotypes occurred in only a single individual. PAH variants were scored using an allelic phenotype value and correlated with pre-treatment blood phenylalanine concentrations (n = 6,115) and tetrahydrobiopterin loading test results (n = 4,381), enabling prediction of both a genotype-based phenotype (88%) and tetrahydrobiopterin responsiveness (83%). This study shows that large genotype databases enable accurate phenotype prediction, allowing appropriate targeting of therapies to optimize clinical outcome.

Improving the Diagnosis of Phenylketonuria by Using a Machine Learning-Based Screening Model of Neonatal MRM Data

Phenylketonuria (PKU) is a common genetic metabolic disorder that affects the infant's nerve development and manifests as abnormal behavior and developmental delay as the child grows. Currently, a triple–quadrupole mass spectrometer (TQ-MS) is a common high-accuracy clinical PKU screening method. However, there is high false-positive rate associated with this modality, and its reduction can provide a diagnostic and economic benefit to both pediatric patients and health providers. Machine learning methods have the advantage of utilizing high-dimensional and complex features, which can be obtained from the patient's metabolic patterns and interrogated for clinically relevant knowledge. In this study, using TQ-MS screening data of more than 600,000 patients collected at the Newborn Screening Center of Shanghai Children's Hospital, we derived a dataset containing 256 PKU-suspected cases. We then developed a machine learning logistic regression analysis model with the aim to minimize false-positive rates in the results of the initial PKU test. The model attained a 95–100% sensitivity, the specificity was improved 53.14%, and positive predictive value increased from 19.14 to 32.16%. Our study shows that machine learning models may be used as a pediatric diagnosis aid tool to reduce the number of suspected cases and to help eliminate patient recall. Our study can serve as a future reference for the selection and evaluation of computational screening methods.

Functional vitamin B12 deficiency in phenylketonuria patients and healthy controls: An evaluation with combined indicator of vitamin B12 status as a biochemical index

BACKGROUND

Vitamin B12 deficiency frequently appears in phenylketonuria patients having a diet poor in natural protein. The aims of this study were to evaluate vitamin B12 status in phenylketonuria patients by using combined indicator of vitamin B12 status (cB12) as well as methylmalonic acid and homocysteine, more specific and sensitive markers, in comparison with healthy controls.

METHODS

Fifty-three children and adolescents with phenylketonuria under dietary treatment and 30 healthy controls were assessed cross-sectionally. Serum vitamin B12 and folate concentrations were analysed by chemiluminescence immunoassay. Plasma methylmalonic acid and total homocysteine concentrations were measured by liquid chromatography-tandem mass spectrometry and liquid chromatography, respectively. cB12 was calculated by using a formula involving blood parameters.

RESULTS

Methylmalonic acid and folate concentrations in phenylketonuria group were higher compared with controls. Methylmalonic acid concentrations were high in 56.5% of the patients and 26.7% of the controls with normal vitamin B12 concentrations. Based on cB12, a significant difference within the normal values was detected between the groups. However, although 24.5% of phenylketonuria patients and 13.3% of controls had decreased vitamin B12 status according to cB12, there was no significant difference.

CONCLUSION

Children and adolescents with phenylketonuria having a strict diet can be at risk of functional vitamin B12 deficiency. This deficiency can be accurately determined by measuring methylmalonic acid concentrations. Calculation of cB12 as a biochemical index did not provide additional information compared with the measurement of methylmalonic acid alone, but may be helpful for classification of some patients with increased methylmalonic acid as having adequate vitamin B12 status.

Characteristics, comorbidities, and use of healthcare resources of patients with phenylketonuria: a population-based study

Background: Phenylketonuria is a well-known disease, yet the characteristics of the affected population and their use of healthcare resources have not been comprehensively evaluated. Patient characteristics and use of resources are subjects of interest for most governments, especially for a disease included in newborn screening programs. Objective: The aim of this study was to determine characteristics and use of healthcare resources of patients with phenylketonuria in the region of Catalonia. Methods: Records of 289 patients admitted with phenylketonuria between 2007 and 2017 were extracted from the PADRIS database that includes admission data from primary care centers, hospitals (inpatient and outpatient care), extended care facilities, and mental health centers. Results: The patient population was composed of 140 male patients and 149 female patients, and 102 patients were registered via newborn screening during the study period. Patients were admitted on average 2.19 times per year, mostly into primary care centers which concentrated the largest portion of direct medical expenses. Similar percentages of urgent and scheduled admissions were registered both in primary care and hospitals. Annual direct medical cost of treating patients with phenylketonuria was €667 per patient. Finally, 66.80% of the patients suffered from chronic conditions affecting two or more systems, likely to correspond to a wide variety of conditions. Conclusions: Altogether, phenylketonuria patient demographics and direct medical costs in Catalonia have been revised. Patients diagnosed with phenylketonuria appeared 1.3-times more likely to suffer from chronic conditions in distinct organ systems, which is expected to have an effect on their use of healthcare resources. These results support the need to adapt and improve the healthcare system, taking multimorbidity into consideration in an effort to control the medical expenses derived.

Admissions and Cost of Hospitalisation of Phenylketonuria: Spanish Claims Database Analysis

BACKGROUND

Phenylketonuria is a well-known rare disease included in the neonatal screening of many countries. Therefore, there are few published data on the admissions and costs of phenylketonuria in Spain.

OBJECTIVE

The objective of this study was to assess the number of admissions and the economic burden of phenylketonuria in Spain.

METHODS

Patients with phenylketonuria were identified from a Spanish database containing data from public and private healthcare centres from 1997 to 2015. The parameters obtained were characteristics of the patients, type of admissions, readmissions, discharges, length of stay, medical service, annual number of visits, annual number of patients, visit-associated costs and patient-associated costs.

RESULTS

Five hundred and ninety-four patients with phenylketonuria were identified: 48.32% were male with a mean (standard deviation) age of 4.50 (10.23) years. The hospital admissions were divided into emergency visits (55.94%) and scheduled visits (43.92%). The majority of patients were discharged home (98.86%). The mean (standard deviation) duration of stay was 4.04 (4.98) days. The number of admissions per year ranged between 13 and 88, with an average of 1.18 admissions per patient per year. Finally, the mean cost per visit increased from €1064.91 to €3709.40, and the mean cost per patient increased from €1818.90 to €4239.32 from 1999 to 2015.

CONCLUSIONS

The access to economic and social data on phenylketonuria in Spain has been updated. The number of admissions in Spain between 1997 and 2015 and healthcare costs between 1999 and 2015 were calculated. There were 24 admissions as a result of a phenylketonuria diagnosis in 2015 and the mean healthcare cost per patient was €4239.32. This information can help to adapt and improve each healthcare system to take into consideration rare diseases.