BH4-deficient hyperphenylalaninemia in Russia

Current Status of Newborn Bloodspot Screening Worldwide 2024: A Comprehensive Review of Recent Activities (2020-2023)

Newborn bloodspot screening (NBS) began in the early 1960s based on the work of Dr. Robert "Bob" Guthrie in Buffalo, NY, USA. His development of a screening test for phenylketonuria on blood absorbed onto a special filter paper and transported to a remote testing laboratory began it all. Expansion of NBS to large numbers of asymptomatic congenital conditions flourishes in many settings while it has not yet been realized in others. The need for NBS as an efficient and effective public health prevention strategy that contributes to lowered morbidity and mortality wherever it is sustained is well known in the medical field but not necessarily by political policy makers. Acknowledging the value of national NBS reports published in 2007, the authors collaborated to create a worldwide NBS update in 2015. In a continuing attempt to review the progress of NBS globally, and to move towards a more harmonized and equitable screening system, we have updated our 2015 report with information available at the beginning of 2024. Reports on sub-Saharan Africa and the Caribbean, missing in 2015, have been included. Tables popular in the previous report have been updated with an eye towards harmonized comparisons. To emphasize areas needing attention globally, we have used regional tables containing similar listings of conditions screened, numbers of screening laboratories, and time at which specimen collection is recommended. Discussions are limited to bloodspot screening.

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.

Biochemical and molecular features of tetrahydrobiopterin deficiency in Fujian Province, southeastern China

The estimated prevalence of tetrahydrobiopterin deficiency (BH4D) and the mutational spectrum of the causal 6-pyruvoyl-tetrahydropterin synthase (PTS) gene vary widely according to race and region. This study assessed the prevalence and genetic characteristics of BH4D in Fujian Province, southeastern China. A total of 3,204,067 newborns were screened between 2012 and 2022 based on the phenylalanine level and the phenylalanine/tyrosine ratio in dried blood spots. Differential diagnosis was determined by the urine purine spectrum, dihydropteridine reductase activity in red blood cells, and genetic testing. The PTS mutation spectrum and genotypes were determined by next-generation sequencing. A total of 189 newborns were diagnosed with hyperphenylalaninemia (HPA) over the study period, including 159 with phenylalanine hydroxylase deficiency and 30 with BH4D. Therefore, the prevalence of BH4D in Fujian was 9.36 per 1,000,000 live births (30/3,204,067) and the proportion of BH4D among patients with HPA was 15.87% (30/189). A total of 58 PTS alleles were identified in the 29 patients with PTS deficiency (PTPSD), and those alleles were composed of 10 different variants, including eight missense variants and two splice-site variants. The most prevalent variants were c.155A>G, p.Asn52Ser (44.83%); c.259C>T, p.Pro87Ser (39.66%); and c.84-291A>G, p.Tyr27Argfs*8 (3.45%). The predominant genotype was c [155A>G]; [259C>T] (11/29, 37.93%). The prevalence of BH4D and the spectrum of associated PTS mutations were successfully determined for the first time in Fujian Province, southeastern China. Since the mutation spectrum of PTS is region-specific, such data will facilitate molecular diagnosis and genetic counseling in PTPSD cases.

Phenotypes and Genotypes of Inherited Disorders of Biogenic Amine Neurotransmitter Metabolism

Inherited disorders of biogenic amine metabolism are genetically determined conditions resulting in dysfunctions or lack of enzymes involved in the synthesis, degradation, or transport of dopamine, serotonin, adrenaline/noradrenaline, and their metabolites or defects of their cofactor or chaperone biosynthesis. They represent a group of treatable diseases presenting with complex patterns of movement disorders (dystonia, oculogyric crises, severe/hypokinetic syndrome, myoclonic jerks, and tremors) associated with a delay in the emergence of postural reactions, global development delay, and autonomic dysregulation. The earlier the disease manifests, the more severe and widespread the impaired motor functions. Diagnosis mainly depends on measuring neurotransmitter metabolites in cerebrospinal fluid that may address the genetic confirmation. Correlations between the severity of phenotypes and genotypes may vary remarkably among the different diseases. Traditional pharmacological strategies are not disease-modifying in most cases. Gene therapy has provided promising results in patients with DYT-DDC and in vitro models of DYT/PARK-SLC6A3. The rarity of these diseases, combined with limited knowledge of their clinical, biochemical, and molecular genetic features, frequently leads to misdiagnosis or significant diagnostic delays. This review provides updates on these aspects with a final outlook on future perspectives.

Mutation spectrum of PTS gene in patients with tetrahydrobiopterin deficiency from jiangxi province

Background: Hyperphenylalaninemia (HPA) is the most common inborn error in amino acid metabolism. It can be primarily classified into phenylalanine hydroxylase (PAH) deficiency and tetrahydrobiopterin (BH4) deficiency. BH4 deficiency (BH4D) is caused by genetic defects in enzymes involved in the biosynthesis and regeneration of BH4. 6-pyruvoyl-tetrahydropterin synthase (PTPS/PTS), which is encoded by the PTS gene, participates in the biosynthesis of BH4. PTPS deficiency (PTPSD) is the major cause of BH4D. In this study, we investigated that the prevalence of BH4D in Jiangxi province was approximately 12.5 per 1,000,000 live births (69/5,541,627). Furthermore, the frequency of BH4D was estimated to be 28.8% (69/240) in the HPA population of Jiangxi. In this study, we aimed to characterize the mutational spectrum of the PTS gene in patients with PTPSD from Jiangxi province. Method: Newborn screening data of Jiangxi province from 1997 to 2021 were analyzed and 53 families with PTPSD were enrolled for the analysis of the PTS gene variants by Sanger sequencing. Results: 106 variants were identified in 106 alleles of 53 patients with PTPSD, including 13 types of variants reported previously, and two novel variants (c.164-36A>G and c.146_147insTG). The predominant variant was c.259C>T (47.2%), followed by c.84-291A>G (19.8%), c.155A>G (8.5%), c.286G>A (6.6%) and c.379C>T (4.7%). Conclusion: The results of this study can not only provide guidance for the molecular diagnosis and genetic counseling in cases of PTPS deficiency but also enrich the PTS mutation database.

Genetic evaluation of hyperphenylalaninemia patients with tetrahydrobiopterin deficiency in Iranian population: Identification of four novel disease-causing variants

BACKGROUND

Hyperphenylalaninemia (HPA) is the most common inborn error of amino acid metabolism worldwide. At least 2% of HPA cases are caused by a deficiency in tetrahydrobiopterin (BH4) metabolism. Genes such as QDPR and PTS are essential in the BH4 metabolism. This study aims to identify disease-causing variants in HPA patients, which may be helpful in genetic counseling and prenatal diagnosis.

METHODS

A total of 10 HPA patients were enrolled in this study. The coding and adjacent intronic regions of PTS and QDPR genes were examined using Sanger sequencing. Protein modeling was also performed for novel identified variants.

RESULTS

Ten patients and a total of 20 alleles were studied, which led to the identification of 10 different variants. All variants identified in PTS and QDPR were missense, except for the c.383_407del variant in the QDPR. Also, three novel variants were identified in the QDPR, including c.79G>T, c.383_407del and c.488G>A, and a novel variant, c.65C>G, in the PTS.

CONCLUSIONS

Despite the genetic similarities in the disease-causing variants, differences were observed in the Asian and European populations with our populations; As a result, similar but more extensive studies are needed to investigate the distribution of disease-causing variants in genes involved in non-PKU hyperphenylalaninemia.

Genotypic spectrum underlying tetrahydrobiopterin metabolism defects: Experience in a single Mexican reference center

Background: Pterin profiles or molecular analyses of hyperphenylalaninemia (HPA) caused by phenylalanine hydroxylase (PAH) deficiency or tetrahydrobiopterin deficiency (BH4D) are not always available in low- or middle-income countries, including Mexico, limiting information regarding the phenotypic and genotypic characteristics of patients exhibiting BH4D.

Objective: To report the genotypes underlying BH4D and the clinical presentation in unrelated Mexican HPA pediatric patients with normal PAH genotypes who attended a single metabolic reference center in Mexico.

Methods: Automated Sanger sequencing of the PTS, QDPR, and PCBD1 genes of 14 HPA patients was performed. Predicted effects on protein structure caused by missense variants were assessed by in silico protein modeling.

Results and discussion: A high prevalence of BH4D was noted in our HPA cohort (9.8%, N = 14/142). Clinically relevant biallelic genotypes were identified in the PTS (N = 7/14 patients), QDPR (N = 6/14 patients), and PCBD1 (N = 1/14 patients) genes. Four novel QDPR variants [c.714dup or p.(Leu239Thrfs*44), c.106-1G>T or p.(?), c.214G>T or p.(Gly72*), and c.187_189dup or p.(Gln63dup)] were identified. In silico protein modeling of six missense variants of PTS [p.(Thr67Met), p.(Glu81Ala), and p.(Tyr113Cys)], QDPR [p.(Cys161Phe) and p.(Pro172Leu)], and PCBD1 [p.(Glu97Lys)] supports their pathogenicity. Progressive neurological symptoms (mainly intellectual and motor impairment and even death in three patients) were noted in all patients with biallelic QDPR genotypes and in 5/7 patients bearing biallelic PTS genotypes. The single homozygous PCBD1 p.(Glu97Lys) patient remains asymptomatic.

Conclusion: A higher proportion of BH4D (9.8 vs. 1%–2% worldwide), attributable to a heterogeneous mutational spectrum and wide clinical presentation, was noted in our Mexican HPA cohort, with the PTS-related HPA disorder being the most frequent. Sequencing-based assays could be a reliable approach for diagnosing BH4D in our population.

In silico analysis and the pathogenicity classification of PTS gene variants among Iranian population

Background

6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is an autosomal recessive disorder caused by PTS gene mutations. The aim of this study was to collect all PTS gene variants detected among Iranian patients with PTPS deficiency as well as in the Iranome project and classify them based on American College of Medical Genetics and Genomics (ACMG-AMP) guidelines.

Results

The number of PTS gene variants reported among Iranian PTPS patients and in the Iranome project were 19 and 36, respectively. Given that one variant was reported in both of our sources, the total number of variants was 54. These variants were classified as pathogenic (n = 11), likely pathogenic (n = 7), VUS (n = 23), likely benign (n = 1), and benign (n = 12). Out of 19 variants reported among Iranian PTPS patients, c.155A>G (p.Asn52Ser, rs104894275) and c.317C>T (p.Thr106Met, rs200712908) were the most frequent ones, each with a frequency of 10%. c.84-3C>G (rs1230781262) (7.5%) and c.281A>T (p.Asp94Val) (5%) were in the next ranks of the list of variants.

Conclusions

The ACMG-AMP criteria need to be updated depending on the type of disease. In addition, to the best of our knowledge, no template has been described for classifying the variants identified in PTPS deficiency. Therefore, this study can be a good reference for future studies in this subject.

Influencing Factors on the Use of Tetrahydrobiopterin in Patients with Phenylketonuria

Objective

To explore and analyze the influencing factors of tetrahydrobiopterin therapy in patients with phenylketonuria.

Methods

86 children with phenylketonuria (PKU) diagnosed and treated in our hospital from February 2019 to September 2021 were randomly enrolled. All the children underwent coenzyme hydroxybiopterin and urinary pterin spectrum analysis, and the children with deficiency received gene mutation testing.

Results

The results of urine pterin analysis showed that 82 patients had higher urinary N and B contents than the normal reference values, with the N/B slightly higher than the normal B% within the normal range. 4 patients had extremely high urinary N/B and B% <5% and were diagnosed as BH4 deficiency caused by 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, and a combined stress test was performed. The blood Phe level was (720-1200) μmol/L 3 h after Phe loading, and the blood Phe concentration decreased to (120-240) μmol/L 4-6 h after oral administration of 7.5 mg/kg BH4 tablet. After one week of treatment, the blood Phe concentration decreased significantly to 239 ± 173 μmol/L, with a decrease rate of 52.14 ± 25.28%. It shows that the application of tetrahydrobiopterin intervention therapy is effective in patients with PKU. The results of the full-length cDNA analysis of the PTPS gene showed that a total of 4 gene mutations were found. A C ⟶ T substitution occurred at the 259th base, and the 87th proline (Pro) in the coding region was converted to serine (Ser) (P87S). G ⟶ A substitution at base 286 converts aspartic acid (Asp) at position 96 of the coding region to asparagine (Asn) (D96N). A ⟶ G substitution occurs at the 155th base to convert asparagine (Asn) at position 52 of the coding region to serine (Ser) (N52S). G ⟶ C substitution occurs at the 430th base to convert glycine at position 144 (Gly) to arginine (Arg) (G144R). G144R is a new mutation type. The gene mutation types of the 4 patients were P87S/D96N, N52S/G144R, D96N/P87S, and P87S/P87S, all of which were from their parents, which conformed to the law of autosomal recessive inheritance.

Conclusion

PKU is caused by the defect of phenylalanine hydroxylase activity in children, which causes phenylalanine metabolism disorder, and tetrahydrobiopterin intervention therapy can affect the activity of phenylalanine hydroxylase, increase the decline rate of blood Phe, significantly reduce the level of phenylalanine in children, and promote intellectual recovery. The dose of tetrahydrobiopterin should be tailored, with small doses for mild phenotypes and long-term treatment using even smaller doses.

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.

Genome-wide selective detection of Mile red-bone goat using next-generation sequencing technology

The ecotype population of goats (Capra hircus) was created by long-term artificial selection and natural adaptation. Mile red-bone goat is an indigenous breed with visible red bones, and its special bone structure has received extensive attention. This study aimed to identify genetic variants and candidate genes associated with specific bone phenotypes using next-generation sequencing technology (NGS). The results revealed that 31,828,206 single nucleotide polymorphisms (SNPs) were obtained from 72 goats (20 Mile red-bone goats and 52 common goats) by NGS. A total of 100 candidate genes were identified on the basis top 1% window interaction from nucleotide diversity (π), π ratio (π A/π B), and pairwise fixation index (F ST). Exactly 77 known signaling pathways were enriched. Specifically, three coding genes (NMNAT2, LOC102172983, and PNLIP) were annotated in the vitamin metabolism signaling pathways, and NCF2 was annotated to the osteoclast (OC) differentiation pathway. Furthermore, 5862 reliable copy number variations (CNVs) were obtained, and 14 and 24 genes were annotated with the top 1‰ CNV based on F ST (>0.490) and V ST (>0.527), respectively. Several pathways related to bone development and metabolism of exogenous substances in vivo, including calcium signaling pathway, OC differentiation, and glycerophospholipid metabolism, were annotated. Specifically, six genes from 19 candidate CNVs, which were obtained by interaction of the top 1‰ CNVs with F ST and V ST, were annotated to mucin-type O-glycan biosynthesis and metabolic pathways. Briefly, the results implied that pseudopurpurin and specific genetic variants work together to contribute to the red-bone color and specific bone structure of Mile red-bone goat. This study is helpful to understanding the genetic basis of the unique bone phenotype of Mile red-bone goats.

Molecular and metabolic bases of tetrahydrobiopterin (BH4) deficiencies

Tetrahydrobiopterin (BH4) deficiency is caused by genetic variants in the three genes involved in de novo cofactor biosynthesis, GTP cyclohydrolase I (GTPCH/GCH1), 6-pyruvoyl-tetrahydropterin synthase (PTPS/PTS), sepiapterin reductase (SR/SPR), and the two genes involved in cofactor recycling, carbinolamine-4α-dehydratase (PCD/PCBD1) and dihydropteridine reductase (DHPR/QDPR). Dysfunction in BH4 metabolism leads to reduced cofactor levels and may result in systemic hyperphenylalaninemia and/or neurological sequelae due to secondary deficiency in monoamine neurotransmitters in the central nervous system. More than 1100 patients with BH4 deficiency and 800 different allelic variants distributed throughout the individual genes are tabulated in database of pediatric neurotransmitter disorders PNDdb. Here we provide an update on the molecular-genetic analysis and structural considerations of these variants, including the clinical courses of the genotypes. From a total of 324 alleles, 11 are associated with the autosomal recessive form of GTPCH deficiency presenting with hyperphenylalaninemia (HPA) and neurotransmitter deficiency, 295 GCH1 variant alleles are detected in the dominant form of L-dopa-responsive dystonia (DRD or Segawa disease) while phenotypes of 18 alleles remained undefined. Autosomal recessive variants observed in the PTS (199 variants), PCBD1 (32 variants), and QDPR (141 variants) genes lead to HPA concomitant with central monoamine neurotransmitter deficiency, while SPR deficiency (104 variants) presents without hyperphenylalaninemia. The clinical impact of reported variants is essential for genetic counseling and important for development of precision medicine.