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Background: The GCH1 gene encodes the enzyme guanosine triphosphate cyclohydrolase I (GTPCH), which catalyzes the rate‐limiting step in the biosynthesis of tetrahydrobiopterin (BH4), a critical cofactor in the production of monoamine neurotransmitters. Autosomal dominant GTPCH (adGTPCH) deficiency is the most common cause of dopa‐responsive dystonia (DRD), whereas the recessive form (arGTPCH) is an ultrarare and poorly characterized disorder with earlier and more complex presentation that may disrupt neurodevelopmental processes. Here, we delineated the phenotypic spectrum of ARGTPCHD and investigated the predictive value of biochemical and genetic correlates for disease outcome. Objectives: The aim was to study 4 new cases of arGTPCH deficiency and systematically review patients reported in the literature. Methods: Clinical, biochemical, and genetic data and treatment response of 45 patients are presented. Results: Three phenotypes were outlined: (1) early‐infantile encephalopathic phenotype with profound disability (24 of 45 patients), (2) dystonia‐parkinsonism phenotype with infantile/early‐childhood onset of developmental stagnation/regression preceding the emergence of movement disorder (7 of 45), and (3) late‐onset DRD phenotype (14 of 45). All 3 phenotypes were responsive to pharmacological treatment, which for the first 2 must be initiated early to prevent disabling neurodevelopmental outcomes. A gradient of BH4 defect and genetic variant severity characterizes the 3 clinical subgroups. Hyperphenylalaninemia was not observed in the second and third groups and was associated with a higher likelihood of intellectual disability. Conclusions: The clinical spectrum of arGTPCH deficiency is a continuum from early‐onset encephalopathies to classical DRD. Genotype and biochemical alterations may allow early diagnosis and predict clinical severity. Early treatment remains critical, especially for the most severe patients. [ABSTRACT FROM AUTHOR]

Background: Hyperphenylalaninemias (HPA) are due to several gene mutations, of which the PAH gene is the most frequently involved. Prevalence and incidence of disease vary between populations, with genotype/phenotype correlations not always capable to correctly predict disease severity. The aim of this study was to give an overview of PAH mutations among one of the largest cohort of patients among Europe, born in Lombardy (Italy) starting from late 1970 s and including over a 60 years of activity; furthermore, to evaluate and discuss identified genotype/phenotype correlations and related reliability. Patients/Methods: Eight hundred and twenty‐six HPA patients in current follow‐up at the San Paolo Hospital in Milan (Italy) were retrospectively reviewed, including molecular results and allelic phenotype and genotype values (attributed on the basis of the APV/GPV system) to verify genotype–phenotype correlations. Results: A total of 166 different PAH variants were reviewed; of those, seven variants were identified as not previously described in literature. Most frequently reported variant was p.Ala403Val, followed by p.Arg261Gln, p.Val245Ala, IVS10‐11 g>a, p.Tyr414Cys and p.Leu48Ser. Phenotype prediction, based on APV/GPV, matched the actual phenotype in most cases, but not always. Conclusion/Discussion: The cohort of patients included in this study constitute a representative sample of the HPA population worldwide. Studies on this sample may allow to improve clinical and genetic evaluation performances for affected patients, consequently to develop personalized medicine interventions and provide more precise indications on the correct treatment approach based on the accumulated evidence, also in light of a prognostically reliable but not always conclusive APV/GPV system. [ABSTRACT FROM AUTHOR]

Increasing evidence suggests the involvement of peripheral amino acid metabolism in the pathophysiology of neuropsychiatric disorders, whereas the molecular mechanisms are largely unknown. Tetrahydrobiopterin (BH4) is a cofactor for enzymes that catalyze phenylalanine metabolism, monoamine synthesis, nitric oxide production, and lipid metabolism. BH4 is synthesized from guanosine triphosphate and regenerated by quinonoid dihydropteridine reductase (QDPR), which catalyzes the reduction of quinonoid dihydrobiopterin. We analyzed Qdpr−/− mice to elucidate the physiological significance of the regeneration of BH4. We found that the Qdpr−/− mice exhibited mild hyperphenylalaninemia and monoamine deficiency in the brain, despite the presence of substantial amounts of BH4 in the liver and brain. Hyperphenylalaninemia was ameliorated by exogenously administered BH4, and dietary phenylalanine restriction was effective for restoring the decreased monoamine contents in the brain of the Qdpr−/− mice, suggesting that monoamine deficiency was caused by the secondary effect of hyperphenylalaninemia. Immunohistochemical analysis showed that QDPR was primarily distributed in oligodendrocytes but hardly detectable in monoaminergic neurons in the brain. Finally, we performed a behavioral assessment using a test battery. The Qdpr−/− mice exhibited enhanced fear responses after electrical foot shock. Taken together, our data suggest that the perturbation of BH4 metabolism should affect brain monoamine levels through alterations in peripheral amino acid metabolism, and might contribute to the development of anxiety‐related psychiatric disorders. Cover Image for this issue: https://doi.org/10.1111/jnc.15398 [ABSTRACT FROM AUTHOR]

Importance: Sapropterin hydrochloride, a natural coenzyme (6R‐tetrahydrobiopterin) of phenylalanine hydroxylase, was first approved as a treatment for tetrahydrobiopterin deficiency in 1992 in Japan, and was then approved as a treatment for a tetrahydrobiopterin‐responsive hyperphenylalaninemia in 2007 and 2008, in the USA and Japan, respectively. Guidelines are required on the proper use of sapropterin hydrochloride for tetrahydrobiopterin‐responsive hyperphenylalaninemia. Observations: It is recommended that tetrahydrobiopterin‐responsive hyperphenylalaninemia should be diagnosed in all cases of hyperphenylalaninemia, including phenylketonuria, by tetrahydrobiopterin administration tests rather than by phenotype or blood phenylalanine levels. Conclusions and Relevance: If tetrahydrobiopterin‐responsive hyperphenylalaninemia is diagnosed, all ages can be treated with sapropterin hydrochloride. Although there are reports that sapropterin hydrochloride is effective and safe for the prevention of maternal phenylketonuria, further investigation is required. [ABSTRACT FROM AUTHOR]

Subtle executive function deficits, particularly regarding inhibitory control, have been reported in patients with phenylketonuria (PKU) despite early dietary treatment. Purpose of this study was to assess whether young female adults with PKU exhibit altered neural activity underlying such deficits, particularly in a fronto-parietal cognitive control network (CCN). Behavioural data and functional magnetic resonance imaging (fMRI) data were acquired during a Go-NoGo task in 16 young adult patients with PKU and 17 control subjects. Hypothesis-driven analyses of behavioural and fMRI data in the CCN were supplemented by exploratory whole brain activation analyses. PKU patients exhibited a trend towards higher errors of commission. Patients exhibited marginally increased activation associated with inhibitory control in only one CCN core region (right middle frontal gyrus, p = .043). Whole brain analyses revealed widespread relatively increased activation in adults with PKU in the main task contrast (NoGo > Go). This increased activation was mainly observed outside the CCN and largely overlapped with the default mode network (DMN). In conclusion, only subtle inhibitory control deficits and associated brain activity differences were observed in young adults with PKU. Thus, this work adds to the notion that this particular population seems to be only slightly affected by such cognitive deficits. While there were also only minimal increases when compared to healthy subjects in brain activity in a cognitive control network, we observed more widespread activation increases outside this network. These results support the assumption of DMN dysfunction in PKU. [ABSTRACT FROM AUTHOR]

Background: Recently hyperphenylalaninemia (HPA) caused by variants in DNAJC12 was reported and this suggested a new strategy for diagnosis. But DNAJC12‐associated HPA is a rare in Chinese population so far. Methods: The clinical information and blood samples from the patient and his family members were collected and analyzed. Whole‐exome sequencing (WES) was used to identify the causative gene. Results: We reported a newborn patient with HPA, having excluded the causes in common genes associated with HPA. By using whole‐exome sequencing, novel compound heterozygosity mutations in DNAJC12 were found, namely c.306C>G (p.His102Gln) and c.182delA (p.Lys61Argfs*6). Administering a diet with low phenylalanine combined with tetrahydrobiopterin and neurotransmitter precursors were shown to be effective in preventing neurodevelopmental delay for these patients. Conclusion: Our finding confirms the diagnosis of DNAJC12‐associated HPA and suggests that genetic detection of DNAJC12 should be considered when newborn screening results are positive for HPA. [ABSTRACT FROM AUTHOR]

The mutational spectrum of the phenylalanine hydroxylase gene ( PAH) in Mexico is unknown, although it has been suggested that PKU variants could have a differential geographical distribution. Genotype-phenotype correlations and genotype-based predictions of responsiveness to tetrahydrobiopterin (BH4) have never been performed. We sequenced the PAH gene and determined the geographic origin of each allele, mini-haplotype associated, genotype-phenotype correlations and genotype-based prediction of BH4 responsiveness in 48 Mexican patients. The mutational spectrum included 34 variants with c.60+5G>T being the most frequent (20.8%) and linked to haplotype 4.3 possibly because of a founder effect and/or genetic drift. Two new variants were found c.1A>T and c.969+6T>C. The genotype-phenotype correlation was concordant in 70.8%. The genotype-based prediction to BH4-responsiveness was 41.7%, this information could be useful for the rational selection of candidates for BH4 testing and therapy. [ABSTRACT FROM AUTHOR]

Tetrahydrobiopterin (BH4) is an essential enzymatic cofactor in the formation of key neurotransmitters and nitric oxide (NO). It also has a cellular protective role as an antioxidant and scavenger of reactive nitrogen or oxygen species. Inherited hyperphenylalaninemia, which is caused by mutations in converting enzymes responsible for BH4 synthesis, was the first reported disease implicating BH4. Oxidative stress can also cause decreased BH4 levels, leading to uncoupling of BH4–nitric oxide synthase (NOS) and diminished NO, further aggravating numerous pathologies. BH4 deficiency is found in cardiovascular, neurodegenerative, and metabolic diseases and is also involved in aging and mitochondrial dysfunction. BH4 supplementation successfully prevents the development or progression of these diseases and thus has valuable clinical potential. [ABSTRACT FROM AUTHOR]

Phenylketonuria (PKU) and related hyperphenylalaninemia (HPA) are caused by a deficiency in hepatic phenylalanine hydroxylase (PAH). The incidence of PKU in Nagasaki prefecture is higher than that in all parts of Japan (1/15 894 vs 1/120 000). To investigate the genetic background of patients with HPA in Nagasaki prefecture, mutation analysis was done in 14 patients with PKU or mild HPA. Homozygous or compound heterozygous PAH mutations were identified in all the patients. The spectrum of PAH mutations in the cohort was broad and similar to those in all parts of Japan and East Asian countries. R53H is the most common mutation in patients with mild HPA. The present results provide further support for genotype-phenotype correlations in patients with HPA. The high incidence of PKU in Nagasaki, the westernmost part of Japan, might be due to migration of people with PAH mutations from China and Korea, and geographic factors. [ABSTRACT FROM AUTHOR]

Hyperphenylalaninemia (Online Mendelian Inheritance in Man ®database: 261600) is an autosomal recessive disorder mainly due to mutations in the gene for phenylalanine hydroxylase; the most severe form of hyperphenylalaninemia is classic phenylketonuria. We sequenced the entire gene for phenylalanine hydroxylase in 51 unrelated hyperphenylalaninemia patients from Southern Italy. The entire locus was genotyped in 46 out of 51 hyperphenylalaninemia patients, and 32 different disease-causing mutations were identified. The pathologic nature of two novel gene variants, namely, c.707-2delA and p.Q301P, was demonstrated by in vitro studies. c.707-2delA is a splicing mutation that involves the accepting site of exon 7; it causes the complete skipping of exon 7 and results in the truncated p.T236MfsX60 protein. The second gene variant, p.Q301P, has very low residual enzymatic activity (∼ 4.4%), which may be ascribed, in part, to a low expression level (8–10%). Both the decreased enzyme activity and the low expression level are supported by analysis of the 3D structure of the molecule. The putative structural alterations induced by p.Q301P are compatible with protein instability and perturbance of monomer interactions within dimers and tetramers, although they do not affect the catalytic site. In vivo studies showed tetrahydrobiopterin responsiveness in the p.Q301P carrier but not in the c.707-2delA carrier. We next investigated genotype–phenotype correlations and found that genotype was a good predictor of phenotype in 76% of patients. However, genotype–phenotype discordance occurred in approximately 25% of our patients, mainly those bearing mutations p.L48S, p.R158Q, p.R261Q and p.P281L. [ABSTRACT FROM AUTHOR]

Aim: To evaluate whether the age at body mass index (BMI) rebound may be associated with overweight at age 8 y in hyperphenylalaninaemic (HPA) children. Methods: A longitudinal observational study including 97 HPA children born 1984-1993 and detected by the National Neonatal Screening programme. Children were followed up at the same institution and evaluated for dietary intakes and anthropometrical parameters from diagnosis up to the age of 8 y. Outcome measure was overweight at age 8 y, defined according to the International Obesity Task Force. The age at BMI rebound, BMI before and at rebound were considered as potential determinants. Familial overweight, breastfeeding and macronutrients intake at age 1 y were considered as confounders. Results: Mean (95% confidence interval [CI]) age at BMI rebound was 5.0 (4.7-5.3) y. At the age of 8 y, 24.7% (95% CI 16.3-33.1%) of children was overweight. Children overweight at the age of 8 y exhibited earlier BMI rebound than non-overweight children (mean difference [95% CI] -2.1 [-2.8 to -1.4] y) and higher BMI from the age of 1 y (mean difference [95% CI] 1.2 [0.9-2.5] kg/m 2 ) onward. Overweight was more likely in children with, rather than without, parental overweight (41.0% vs 19.8%). After adjustment for confounders, logistic analysis showed that earlier BMI rebound (odds ratio [OR] 2.4, 95% CI 1.2-4.8) and BMI at age 1 y (OR 2.3, 95%CI 1.1-4.98) were independently associated with overweight at the age of 8 y. Conclusion: Within the population of this study, overweight at age 8 y was positively associated with early BMI rebound and BMI at age 1 y. [ABSTRACT FROM AUTHOR]

The natural cofactor of phenylalanine hydroxylase (PAH), tetrahydrobiopterin (BH4), regulates the enzyme activity as well as being essential in catalysis. BH4-responsive PAH deficiency is a variant of hyperphenylalaninemia or phenylketonuria (PKU) caused by mutations in the human PAH gene that respond to oral BH4 loading by stimulating enzyme activity and therefore lowering serum phenylalanine. Here, we showed in a coupled transcription–translation in vitro assay that upon expression in the presence of BH4, wild-type PAH enzyme activity was enhanced. We then investigated the effect of BH4 on PAH activity in transgenic mice that had a complete or partial deficiency in the endogenous cofactor biosynthesis. The rate of hepatic PAH enzyme activity increased significantly with BH4 content without affecting gene expression or Pah-mRNA stability. These results indicate that BH4 has a chaperon-like effect on PAH synthesis and/or is a protecting cofactor against enzyme auto-inactivation and degradation also in vivo. Our findings thus contribute to the understanding of the regulation of PAH by its cofactor BH4 on an additional level and provide a molecular explanation for cofactor-responsive PKU. [Copyright &y& Elsevier]

Phenylketonuria (PKU) is a metabolic disorder accumulating phenylalanine (Phe) and its metabolites in plasma and tissues of the patients. Considering that phenylalanine is the main neurotoxic metabolite, and brain energy homeostasis seems to be affected in phenylketonuria, our main objective was to investigate the effect of acute and chronic hyperphenylalaninemia (HPA) on creatine kinase (CK) activity in brain cortex of Wistar rats. Hyperphenylalaninemia was induced by subcutaneous administration of 5.2 μmol phenylalanine + 2.4 μmol α-methylphenylalanine (phenylalanine hydroxylase (PAH) inhibitor)/g of body weight. We also investigated the in vitro effect of phenylalanine and/or α-methylphenylalanine on creatine kinase activity in the brain cortex of non-treated rats. The results showed that phenylalanine significantly inhibited creatine kinase activity in vitro and reduced the enzyme activity in vivo. Considering the importance of creatine kinase for the maintenance of energy homeostasis in brain, if this enzyme inhibition also occurs in phenylketonuric patients, it is possible that creatine kinase inhibition may be one of the mechanisms by which phenylalanine is neurotoxic in phenylketonuria. [Copyright &y& Elsevier]

Abstract: To explore the molecular etiology of two disorders caused by a defect in GTP cyclohydrolase I—hereditary progressive dystonia with marked diurnal flucturation (HPD), also known as dopa-responsive dystonia (DRD), and autosomal recessive GTP cyclohydrolase I deficiency—we purified and analyzed recombinant human wild-type and mutant GTP cyclohydrolase I proteins expressed in Escherichia coli. Mutant proteins showed very low enzyme activities, and some mutants were eluted at a delayed volume on gel filtration compared with the recombinant wild-type. Next, we examined the GTP cyclohydrolase I protein amount by western blot analysis in phytohemagglutinin-stimulated mononuclear blood cells from HPD/DRD patients. We found a great reduction in the amount of the enzyme protein not only in one patient who had a frameshift mutation, but also in an HPD/DRD patient who had a missense mutation. These results suggest that a dominant-negative effect of chimeric protein composed of wild-type and mutant subunits is unlikely as a cause of the reduced enzyme activity in HPD/DRD patients. We suggest that reduction of the amount of the enzyme protein, which is independent of the mutation type, could be a reason for the dominant inheritance in HPD/DRD. [ABSTRACT FROM AUTHOR]

Background: Genetic heterogeneity and compound heterozygosis give rise to a continuous spectrum of phenylalanine hydroxylase deficiency and metabolic phenotypes in phenylketonuria (PKU). The most used parameters for evaluating phenotype in PKU are pretreatment phenylalanine (Phe) levels, tolerance for dietary Phe, and Phe overloading test. Phenotype can vary from a "classic" (severe) form to mild hyperphenylalaninemia, which does not require dietary treatment. A subset of patients is responsive to treatment by the cofactor tetrahydrobiopterin (BH4). Genotypes of PKU patients from Rio de Janeiro, Brazil, were compared to predicted and observed phenotypes. Genotype‐based estimations of responsiveness to BH4 were also conducted. Methods: Phenotype was defined by pretreatment Phe levels. A standard prediction system based on arbitrary assigned values was employed to measure genotype‐phenotype concordance. Patients were also estimated as BH4‐responders according to the responsiveness previously reported for their mutations and genotypes. Results: A 48.3% concordance rate between genotype‐predicted and observed phenotypes was found. When the predicted phenotypes included those reported at the BIOPKU database, the concordance rate reached 77%. A total of 18 genotypes from 30 patients (29.4%) were estimated as of potential or probable BH4 responsiveness. Inconsistencies were observed in genotypic combinations including the common "moderate" mutations p.R261Q, p.V388M, and p.I65T and the mild mutations p.L48S, p.R68S, and p.L249F. Conclusion: The high discordance rate between genotype‐predicted and observed metabolic phenotypes in this study seems to be due partially to the high frequency of the so‐called "moderate" common mutations, p.R261Q, p.V388M, and p.I65T, which are reported to be associated to erratic or more severe than expected metabolic phenotypes. Although our results of BH4 estimated responsiveness must be regarded as tentative, it should be emphasized that genotyping and genotype‐phenotype association studies are important in selecting patients to be offered a BH4 overload test, especially in low‐resource settings like Brazil. [ABSTRACT FROM AUTHOR]