Neonatal dopa-responsive extrapyramidal syndrome in twins with recessive GTPCH deficiency

Developmental delay and non-phenylketonuria (PKU) hyperphenylalaninemia in DNAJC12 deficiency: Case and approach

BACKGROUND

Hyperphenylalaninemia is a biomarker for several monogenic neurotransmitter disorders where the body cannot metabolise phenylalanine to tyrosine. Biallelic pathogenic variants in DNAJC12, co-chaperone of phenylalanine, tyrosine, and tryptophan hydroxylases, leads to hyperphenylalaninemia and biogenic amines deficiency.

METHODS AND RESULTS

A male firstborn to non-consanguineous Sudanese parents had hyperphenylalaninemia 247 µmol/L [reference interval (RI) < 200 µmol/L] at newborn screening. Dried blood spot dihydropteridine reductase (DHPR) assay and urine pterins were normal. He had severe developmental delay and autism spectrum disorder without a notable movement disorder. A low phenylalanine diet was introduced at two years without any clinical improvements. Cerebrospinal fluid (CSF) neurotransmitters at five years demonstrated low homovanillic acid (HVA) 0.259 µmol/L (reference interval (RI) 0.345-0.716) and 5-hydroxyindoleaetic acid (5HIAA) levels 0.024 µmol/L (reference interval (RI) 0.100-0.245). Targeted neurotransmitter gene panel analysis identified a homozygous c.78 + 1del variant in DNAJC12. At six years, he was commenced on 5-hydroxytryptophan 20 mg daily, and his protein-restricted diet was liberalised, with continued good control of phenylalanine levels. Sapropterin dihydrochloride 7.2 mg/kg/day was added the following year with no observable clinical benefits. He remains globally delayed with severe autistic traits.

CONCLUSIONS

Urine, CSF neurotransmitter studies, and genetic testing will differentiate between phenylketonuria, tetrahydrobiopterin or DNAJC12 deficiency, with the latter characterised by a clinical spectrum ranging from mild autistic features or hyperactivity to severe intellectual disability, dystonia, and movement disorder, normal DHPR, reduced CSF HIAA and HVA. DNAJC12 deficiency should be considered early in the differential workup of hyperphenylalaninemia identified from newborn screening, with its genotyping performed once deficiencies of phenylalanine hydroxylase (PAH) and tetrahydrobiopterin (BH4) have been biochemically or genetically excluded.

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.

Two Cases of Monozygotic Twins with Early-onset Isolated (DYT1) Dystonia Effectively Treated with Bilateral Globus Pallidus Internus Stimulation

Early-onset isolated (DYT1) dystonia is one of the most common forms of primary dystonia in childhood, and deep brain stimulation of the globus pallidus internus (GPi-DBS) is a highly effective treatment for it. However, the effectiveness of GPi-DBS in monozygotic twins with DYT1 dystonia has never been reported globally. Here, we report the cases of monozygotic twins with DYT1 dystonia who were treated using GPi-DBS, and we include a literature review. The younger brother showed an abnormal gait, with external rotation of the right lower leg at 6 years old. The symptoms gradually became so severe that he had difficulty walking on his own at 9 years of age. Treatment with levodopa-carbidopa partially resolved his symptoms, but most of the symptoms remained. Meanwhile, the older brother developed dystonia in both upper limbs at 8 years of age, with gradual symptom progression. At 13 years of age, they were diagnosed with DYT1 dystonia. Bilateral GPi-DBS was performed in both patients at 16 years of age. Their symptoms remarkably improved after surgery. The Burke-Fahn-Marsden dystonia rating scale (BFMDRS) movement score was reduced from 52 to 2 points for the younger brother and from 35 to 1 point for the older brother. Even if monozygotic twins have the same genes, the onset and severity of symptoms might vary in accordance with differences in epigenomic profiles. However, GPi-DBS treatment was very effective for the two cases; thus, we should consider the surgical interventions for each patient.

Case Report: Severe Hypotonia Without Hyperphenylalaninemia Caused by a Homozygous GCH1 Variant: A Case Report and Literature Review

Dopa-responsive dystonia (DRD) comprises a group of rare but treatable dystonias that exhibit diurnal fluctuation. The GCH1 gene encodes GTP cyclohydrolase-1 (GTPCH-І), a protein that catalyzes the first rate-limiting step of tetrahydrobiopterin biosynthesis. Pathogenic variants in GCH1 are the most common causes of DRD. However, the autosomal recessive form of DRD caused by biallelic GCH1 variants is very rare. Homozygous GCH1 variants have been associated with two clinically distinct human diseases: hyperphenylalaninemia, and DRD with or without hyperphenylalaninemia. Here, we describe one patient who presented during infancy with severe truncal hypotonia and motor developmental regression but without diurnal fluctuation and hyperphenylalaninemia. Treatment with levodopa/carbidopa resulted in the complete and persistent remission of clinical symptoms without any side effects. This was accompanied by age-appropriate neurological development during follow-up. A homozygous GCH1 variant (c.604G>A/p.V202I) was identified in the patient. To our knowledge, this is the first Chinese case of DRD caused by a homozygous GCH1 variant, thus expanding the spectrum of DRD phenotypes. Autosomal recessive DRD that is associated with homozygous GCH1 variants should be considered in patients with severe truncal hypotonia, with or without diurnal fluctuation, even if there is an absence of limb dystonia and hyperphenylalaninemia.

Atremorine in Parkinson's disease: From dopaminergic neuroprotection to pharmacogenomics

Atremorine is a novel bioproduct obtained by nondenaturing biotechnological processes from a genetic species of Vicia faba. Atremorine is a potent dopamine (DA) enhancer with powerful effects on the neuronal dopaminergic system, acting as a neuroprotective agent in Parkinson's disease (PD). Over 97% of PD patients respond to a single dose of Atremorine (5 g, p.o.) 1 h after administration. This response is gender-, time-, dose-, and genotype-dependent, with optimal doses ranging from 5 to 20 g/day, depending upon disease severity and concomitant medication. Drug-free patients show an increase in DA levels from 12.14 ± 0.34 pg/ml to 6463.21 ± 1306.90 pg/ml; and patients chronically treated with anti-PD drugs show an increase in DA levels from 1321.53 ± 389.94 pg/ml to 16,028.54 ± 4783.98 pg/ml, indicating that Atremorine potentiates the dopaminergic effects of conventional anti-PD drugs. Atremorine also influences the levels of other neurotransmitters (adrenaline, noradrenaline) and hormones which are regulated by DA (e.g., prolactin, PRL), with no effect on serotonin or histamine. The variability in Atremorine-induced DA response is highly attributable to pharmacogenetic factors. Polymorphic variants in pathogenic (SNCA, NUCKS1, ITGA8, GPNMB, GCH1, BCKDK, APOE, LRRK2, ACMSD), mechanistic (DRD2), metabolic (CYP2D6, CYP2C9, CYP2C19, CYP3A4/5, NAT2), transporter (ABCB1, SLC6A2, SLC6A3, SLC6A4) and pleiotropic genes (APOE) influence the DA response to Atremorine and its psychomotor and brain effects. Atremorine enhances DNA methylation and displays epigenetic activity via modulation of the pharmacoepigenetic network. Atremorine is a novel neuroprotective agent for dopaminergic neurons with potential prophylactic and therapeutic activity in PD.

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.

Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH4) deficiencies

BACKGROUND

Tetrahydrobiopterin (BH4) deficiencies comprise a group of six rare neurometabolic disorders characterized by insufficient synthesis of the monoamine neurotransmitters dopamine and serotonin due to a disturbance of BH4 biosynthesis or recycling. Hyperphenylalaninemia (HPA) is the first diagnostic hallmark for most BH4 deficiencies, apart from autosomal dominant guanosine triphosphate cyclohydrolase I deficiency and sepiapterin reductase deficiency. Early supplementation of neurotransmitter precursors and where appropriate, treatment of HPA results in significant improvement of motor and cognitive function. Management approaches differ across the world and therefore these guidelines have been developed aiming to harmonize and optimize patient care. Representatives of the International Working Group on Neurotransmitter related Disorders (iNTD) developed the guidelines according to the SIGN (Scottish Intercollegiate Guidelines Network) methodology by evaluating all available evidence for the diagnosis and treatment of BH4 deficiencies.

CONCLUSION

Although the total body of evidence in the literature was mainly rated as low or very low, these consensus guidelines will help to harmonize clinical practice and to standardize and improve care for BH4 deficient patients.

Expanding the Spectrum of Dopa-Responsive Dystonia (DRD) and Proposal for New Definition: DRD, DRD-plus, and DRD Look-alike

Previously, we defined DRD as a syndrome of selective nigrostriatal dopamine deficiency caused by genetic defects in the dopamine synthetic pathway without nigral cell loss. DRD-plus also has the same etiologic background with DRD, but DRD-plus patients have more severe features that are not seen in DRD because of the severity of the genetic defect. However, there have been many reports of dystonia responsive to dopaminergic drugs that do not fit into DRD or DRD-plus (genetic defects in the dopamine synthetic pathway without nigral cell loss). We reframed the concept of DRD/DRD-plus and proposed the concept of DRD look-alike to include the additional cases described above. Examples of dystonia that is responsive to dopaminergic drugs include the following: transportopathies (dopamine transporter deficiency; vesicular monoamine transporter 2 deficiency); SOX6 mutation resulting in a developmentally decreased number of nigral cells; degenerative disorders with progressive loss of nigral cells (juvenile Parkinson's disease; pallidopyramidal syndrome; spinocerebellar ataxia type 3), and disorders that are not known to affect the nigrostriatal dopaminergic system (DYT1; GLUT1 deficiency; myoclonus-dystonia; ataxia telangiectasia). This classification will help with an etiologic diagnosis as well as planning the work up and guiding the therapy.

A proposed nosology of inborn errors of metabolism

Purpose

We propose a nosology for inborn errors of metabolism that builds on their recent redefinition.

Methods

We established a strict definition of criteria in order to develop a self-consistent schema for inclusion of a disorder into the nosology.

Results

We identified 1,015 well-characterized inborn errors of metabolism described in the literature. In addition, there are 111 less well-characterized conditions that may be inborn errors but do not meet strict criteria for inclusion in the current nosology.

Conclusion

We provide a master list of all currently recognized inborn errors of metabolism grouped according to their pathophysiological basis, with the hope of setting a standard against which new errors should be defined, as well as to promote awareness and foster collaboration in the area. With the rapid advances in the field of genetics in recent years, it is likely that this nosology will need to be updated in the near future, a process that will benefit from broader input and collaboration of experts in the field in order to improve future versions of the proposed classification.

Neonatal hypertonia - a diagnostic challenge

In comparison to hypotonia, hypertonia is less commonly expressed in the neonatal period. The scientific literature on the causes of neonatal hypertonia is scant, with no suggested diagnostic algorithm easily available to clinicians. Aetiologies include conditions affecting the central nervous system and spine, and rare peripheral neuromuscular disorders leading to hypertonia. Aetiology onset may be antepartum, peripartum with either transient hypertonia or persistent hypertonia which may appear later, or from a postnatal event/disease. This review discusses neonatal hypertonia and a diagnostic approach to neonatal hypertonia is suggested.

The genetics of dystonia: new twists in an old tale

Dystonia is a common movement disorder seen by neurologists in clinic. Genetic forms of the disease are important to recognize clinically and also provide valuable information about possible pathogenic mechanisms within the wider disorder. In the past few years, with the advent of new sequencing technologies, there has been a step change in the pace of discovery in the field of dystonia genetics. In just over a year, four new genes have been shown to cause primary dystonia (CIZ1, ANO3, TUBB4A and GNAL), PRRT2 has been identified as the cause of paroxysmal kinesigenic dystonia and other genes, such as SLC30A10 and ATP1A3, have been linked to more complicated forms of dystonia or new phenotypes. In this review, we provide an overview of the current state of knowledge regarding genetic forms of dystonia—related to both new and well-known genes alike—and incorporating genetic, clinical and molecular information. We discuss the mechanistic insights provided by the study of the genetic causes of dystonia and provide a helpful clinical algorithm to aid clinicians in correctly predicting the genetic basis of various forms of dystonia.

Movement disorders in children: recent advances in management

In recent years there has been a growing interest towards pediatric movement disorders (PMD). The data derived from the synthesis of clinical observation, neuroimaging, biochemical and, molecular genetics studies have allowed for the identification of a significant number of pediatric diseases featuring movement disorders. The purpose of this review is to outline an approach to the advances in management of dystonia, neurotransmitter disorders, tics, and paroxysmal dyskinetic syndromes starting in children younger than 18 yr of age.

Predisposition of genetic disease by modestly decreased expression of GCH1 mutant allele

Recently it was shown that single nucleotide polymorphisms (SNPs) can explain individual variation because of the small changes of the gene expression level and that the 50% decreased expression of an allele might even lead to predisposition to cancer. In this study, we found that a decreased expression of an allele might cause predisposition to genetic disease. Dopa responsive dystonia (DRD) is a dominant disease caused by mutations in GCH1 gene. The sequence analysis of the GCH1 in a patient with typical DRD symptoms revealed two novel missense mutations instead of a single dominant mutation. Family members with either of the mutations did not have any symptoms of DRD. The expression level of a R198W mutant allele decreased to about 50%, suggesting that modestly decreased expression caused by an SNP should lead to predisposition of a genetic disease in susceptible individuals.

Neonatal Hypertonia: II. differential diagnosis and proposed neuroprotection

More accurate documentation of a neonate's specific hypertonic state could be helpful as part of serial neurologic examinations. The clinician would then be in a more advantageous position to choose the appropriate neuroprotective drug or the procedure that best fits with the etiology, localization, and timing of injury. Ideally, choices for neuroprotection will integrate history, examination, and diagnostic findings before considering options for prophylaxis, neurorescue, or neurorepair. Measuring the efficacy of a neuroprotection protocol should include a complete list of life-course challenges, including motor, epileptic, cognitive, and behavioral outcomes as expressed at successively older ages.

Dominant versus recessive: molecular mechanisms in metabolic disease

Inborn errors of metabolism used to be regarded as simple monogenic traits, but a closer look at how different alleles of a gene determine different phenotypes shows that the molecular mechanisms in the individual case are often complicated. Most metabolic disorders represent a spectrum of phenotypes from normal via attenuated to severe (and sometimes prenatally fatal), and disease manifestation is often influenced by other specific genetic or exogenous factors. The terms 'dominant' or 'recessive' relate to the functional consequences of differing alleles in the (compound) heterozygous individual; the terms are irrelevant for homozygous individuals and inappropriate for X-linked disorders. Mutations affecting the same amino acid residue may be associated with different inheritance patterns. True dominant inheritance in metabolism is rare; it may be found e.g. in tightly regulated biosynthetic pathways or when minor changes in metabolite concentrations have a functional effect. Some disorders such as erythropoietic protoporphyria show pseudodominant inheritance due to prevalent loss-of-function polymorphisms in the general population and are better acknowledged as recessive traits. The term 'variable expressivity' is not helpful with regard to autosomal recessive disorders when variable phenotypes are explained by different mutations in the respective gene. Clonal unmasking of a heterozygous mutation through somatic loss of the second allele, the main pathomechanism in inherited tumour predisposition syndromes, is rare in metabolic disorders, but focal congenital hyperinsulinism is a notable exception. Somatic mosaicism for an OTC gene mutation is given as an example of an apparently heterozygous mutation pattern in a boy with an X-linked disease.

Autosomal recessive GTP cyclohydrolase I deficiency without hyperphenylalaninemia: evidence of a phenotypic continuum between dominant and recessive forms

We describe a unique presentation of autosomal recessive (AR) GTP cyclohydrolase I (GTPCH) deficiency, with severe CNS involvement but without hyperphenylalaninemia. A male infant presented with progressive spasticity, dystonia and oculogyric episodes. Blood phenylalanine levels were persistently normal: whereas an oral phenylalanine loading test revealed impaired phenylalanine clearance. CSF neopterin and tetrahydrobiopterin (BH(4)) were low, homovanillic acid marginally low and 5-hydroxyindoleacetic acid normal. Fibroblasts showed decreased GTPCH enzyme activity. A homozygous novel mutation of GCH1, p.V206A, was identified. On treatment (BH(4), L-Dopa/Carbidopa and 5-hydroxytryptophan), motor development improved. Mutational analysis provided neonatal diagnosis of a younger brother who, after 18 months on treatment, shows normal development. AR GTPCH I deficiency can present without hyperphenylalaninemia and with normal or subtle CSF neurotransmitter profiles. Testing for GTPCH deficiency should be considered for patients with unexplained neurological symptoms and extrapyramidal movement disorder.

GTP-cyclohydrolase I gene mutations in patients with autosomal dominant and recessive GTP-CH1 deficiency: identification and functional characterization of four novel mutations

GTP-cyclohydrolase I (GTP-CH1, EC 3.5.4.16) is encoded by the GCH1 gene. Mutations in the GCH1 gene cause both dopa-responsive dystonia (McKusick 128230) and recessive GTP-CH1 deficiency (McKusick 600225). The exact molecular mechanism resulting in decreased GTP-CH1 activity in the patients is still obscure. We report the clinical features and molecular and functional study of the GCH1 gene in eight Italian patients affected by dominant and recessive GTP-CH1 deficiency. All the studied patients had mutations in the GCH1 gene. Three missense mutations (V205G, K224R, P199A), a frameshift mutation (Delta G693), and a splice-site mutation (ivs5 + 1g > c) were found. Except for K224R these are all novel mutations. To analyse the defect caused by the novel mutations, an in vivo functional assay in a Saccharomyces cerevisiae strain lacking the endogenous gene encoding GTP-CH1 ( FOL2 ) was performed. Complementation analysis showed that the Delta G693 and V205G mutations abolish the enzymatic function, while the P199A mutation causes a conditional defect. In conclusion, the clinical phenotypes displayed by our patients confirm the wide clinical spectrum of the disease and further support the lack of correlation between a given mutation and a clinical phenotype. Complementation analysis in yeast is a useful tool for confirming the pathogenetic effect of GCH1 mutations.

The lumbar puncture for diagnosis of pediatric neurotransmitter diseases

The investigation of infants and children with suspected pediatric neurotransmitter diseases affecting serotonin and catecholamine metabolism is complicated because the measurement of metabolites in peripheral fluids is generally uninformative. Disorders that affect catecholamine (dopamine and norepinephrine) and serotonin neurotransmission, and that do not present with hyperphenylalaninemia, require that a lumbar puncture be performed and that specific metabolites be assessed in the collected cerebrospinal fluid. This review will discuss the disorders affecting catecholamine and serotonin biosynthesis, sample collection and handling, diagnostic methods and expected profiles, problems with diagnosis, and as yet to be described conditions that might be detected using current diagnostic methodologies.