Clinical and genetic studies in a family with a novel mutation in the sepiapterin reductase gene

Peripheralized sepiapterin reductase inhibition as a safe analgesic therapy

The development of novel analgesics for chronic pain in the last 2 decades has proven virtually intractable, typically failing due to lack of efficacy and dose-limiting side effects. Identified through unbiased gene expression profiling experiments in rats and confirmed by human genome-wide association studies, the role of excessive tetrahydrobiopterin (BH4) in chronic pain has been validated by numerous clinical and preclinical studies. BH4 is an essential cofactor for aromatic amino acid hydroxylases, nitric oxide synthases, and alkylglycerol monooxygenase so a lack of BH4 leads to a range of symptoms in the periphery and central nervous system (CNS). An ideal therapeutic goal therefore would be to block excessive BH4 production, while preventing potential BH4 rundown. In this review, we make the case that sepiapterin reductase (SPR) inhibition restricted to the periphery (i.e., excluded from the spinal cord and brain), is an efficacious and safe target to alleviate chronic pain. First, we describe how different cell types that engage in BH4 overproduction and contribute to pain hypersensitivity, are themselves restricted to peripheral tissues and show their blockade is sufficient to alleviate pain. We discuss the likely safety profile of peripherally restricted SPR inhibition based on human genetic data, the biochemical alternate routes of BH4 production in various tissues and species, and the potential pitfalls to predictive translation when using rodents. Finally, we propose and discuss possible formulation and molecular strategies to achieve peripherally restricted, potent SPR inhibition to treat not only chronic pain but other conditions where excessive BH4 has been demonstrated to be pathological.

Relevance of Fluorodopa PET Scan in Dopamine Responsive Dystonia and Juvenile Parkinsonism: A Systematic Review

BACKGROUND

Dopamine Responsive Dystonia (DRD) and Juvenile Parkinsonism (JP) are two diseases commonly presenting with parkinsonian symptoms in young patients. Current clinical guidelines offer a diagnostic approach based on molecular analysis. However, developing countries have limitations in terms of accessibility to these tests. We aimed to assess the utility of imaging equipment, usually more available worldwide, to help diagnose and improve patients' quality of life with these diseases.

METHODS

We performed a systematic literature review in English using the preferred reporting items for systematic reviews and meta-analyses (PRISMA) and meta-analysis of observational studies in epidemiology (MOOSE) protocols. We only used human clinical trials about dopamine responsive dystonia and juvenile parkinsonism patients in which a fluorodopa (FD) positron emission tomography (PET) scan was performed to identify its use in these diseases.

RESULTS

We included six studies that fulfilled our criteria. We found a clear pattern of decreased uptake in the putamen and caudate nucleus in JP cases. At the same time, the results in DRD were comparable to normal subjects, with only a slightly decreased marker uptake in the previously mentioned regions by the FD PET scan.

CONCLUSIONS

We found a distinctive pattern for each of these diseases. Identifying these findings with FD PET scans can shorten the delay in making a definitive diagnosis when genetic testing is unavailable, a common scenario in developing countries.

Recognizing Atypical Dopa-Responsive Dystonia and Its Mimics

Purpose of Review

Dopa-responsive dystonia (DRD) encompasses a group of phenotypically and genetically heterogeneous neurochemical disorders. Classic GTP cyclohydrolase 1 (GCH-1)-associated DRD consists of early-onset lower limb asymmetrical dystonia, with sleep benefit, diurnal variation, and excellent and sustained response to low l-dopa doses.

Recent Findings

Unlike the classic phenotype, GCH-1-associated DRD may include features inconsistent with the original phenotype. We describe a GCH-1-associated late-onset DRD case with a family history of parkinsonism and cervical dystonia whose response to levodopa was poor and complicated with dyskinesia, blepharospasm, and severe nonmotor symptoms. We use this case as a springboard to review the spectrum of atypical DRD, DRD-plus, and DRD mimics.

Summary

GCH-1-related dystonia may exhibit wide intrafamilial phenotypic variability, no diurnal fluctuation, poor response to l-dopa, and such complications as dyskinesia, epilepsy, sleep disorders, autonomic dysfunction, oculogyric crisis, myoclonus, or tics. More recently, rare GCH-1 variants have been found to be associated with Parkinson disease. Clinicians should be aware of atypical DRD, DRD-plus, and DRD mimics.

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.

Spotlight on Oculogyric Crisis: A Review

BACKGROUND

Oculogyric crisis (OGC) is a form of acute dystonia characterized by sustained dystonic, conjugate, and upward deviation of the eyes. It was initially reported in patients with postencephalitic parkinsonism. But later, other factors such as medications, movement disorders, metabolic disorders, and focal brain lesions were also found to be associated with OGC.

METHODS

The literature regarding OGC was searched via PubMed, Google Scholar, and through citations in relevant articles till December 2019, with keywords including OGC, oculogyric eye movements, tonic eye movement, neuroleptics and OGC, antipsychotics and OGC, and all combinations of these. Only original articles (abstract or full text) that were published in the English language were reviewed.

RESULTS

Hypodopaminergic state is implicated in the pathogenesis of OGC. Common risk factors are younger age, male sex, severe illness, high neuroleptic dose, parenteral administration of neuroleptics, high potency of neuroleptic drugs, abrupt discontinuation of anticholinergic medication, and family history of dystonia.

CONCLUSION

OGC is an acute dystonic reaction leading to tonic upward deviation of eyes. It is associated with various neurometabolic, neurodegenerative, and movement disorders and medications such as antipsychotics, antiemetics, antidepressants, antiepileptics, and antimalarials. OGC can adversely impact the compliance and prognosis of the primary illness. Hence, it needs to be managed at earlier stages with appropriate medication, primarily anticholinergics.

Sepiapterin reductase: Characteristics and role in diseases

Sepiapterin reductase, a homodimer composed of two subunits, plays an important role in the biosynthesis of tetrahydrobiopterin. Furthermore, sepiapterin reductase exhibits a wide distribution in different tissues and is associated with many diseases, including brain dysfunction, chronic pain, cardiovascular disease and cancer. With regard to drugs targeting sepiapterin reductase, many compounds have been identified and provide potential methods to treat various diseases. However, the underlying mechanism of sepiapterin reductase in many biological processes is unclear. Therefore, this article summarized the structure, distribution and function of sepiapterin reductase, as well as the relationship between sepiapterin reductase and different diseases, with the aim of finding evidence to guide further studies on the molecular mechanisms and the potential clinical value of sepiapterin reductase. In particular, the different effects induced by the depletion of sepiapterin reductase or the inhibition of the enzyme suggest that the non-enzymatic activity of sepiapterin reductase could function in certain biological processes, which also provides a possible direction for sepiapterin reductase research.

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.

Evaluation of the silkworm lemon mutant as an invertebrate animal model for human sepiapterin reductase deficiency

Human sepiapterin reductase (SR) deficiency is an inherited disease caused by SPR gene mutations and is a monoamine neurotransmitter disorder. Here, we investigated whether the silkworm lemon mutant could serve as a model of SR deficiency. A point mutation in the BmSPR gene led to a five amino acid deletion at the carboxyl terminus in the lemon mutant. In addition, classical phenotypes seen in SR deficient patients were observed in the lemon mutant, including a normal phenylalanine level, a decreased dopamine and serotonin content, and an increased neopterin level. A recovery test showed that the replenishment of l-dopa significantly increased the dopamine level in the lemon mutant. The silkworm lemon mutant also showed negative behavioural abilities. These results suggest that the silkworm lemon mutant has an appropriate genetic basis and meets the biochemical requirements to be a model of SR deficiency. Thus, the silkworm lemon mutant can serve as a candidate animal model of SR deficiency, which may be helpful in facilitating accurate diagnosis and effective treatment options of SR deficiency.

Genetic study in a family with dopa-responsive dystonia revealed a novel mutation in sepiapterin reductase gene

Dopa-responsive dystonia due to sepiapterin reductase deficiency (OMIM#612716) is caused by recessive mutations in the gene encoding sepiapterin reductase (SPR), which plays an important role in the biosynthesis of tetrahydrobiopterin (BH4). One Jordanian patient to first cousin parents is reported in this study. The parents of the proband have recognized the symptoms of their daughter at six months old with motor developmental delay. The symptoms were progressed after-then to include speech delay, seizure, ataxia, oculomotor apraxia, dysarthia and choreoathetosis. Despite of these symptoms, the clinicians in Jordan were unable to diagnose the case. In August 2018, the proband (8 years old) was presented to the department of biotechnology and genetic engineering at Philadelphia University in Jordan for the purposes of performing whole exome sequencing (WES). Analysis of WES data has revealed novel homozygous frameshift variant in the gene SPR (NM_003124.4:c.40delG,p.Ala15Profs*100). The variant is heterozygous in the parents and in the healthy male siblings. Therefore, the studied case was diagnosed with sepiapterin reductase deficiency. Because this disease is likely to be treated recommendations were given to the family immediately to start treatments trials. The case in this study illustrates the difficulties of diagnosing sepiapterin reductase deficiency based on clinical symptoms only and thus renders the possibilities of early management. Also, this study reinforces the importance of running WES to undiagnosed neurodevelopmental cases.

Eye movement disorders and neurological symptoms in late-onset inborn errors of metabolism

Inborn errors of metabolism in adults are still largely unexplored. Despite the fact that adult‐onset phenotypes have been known for many years, little attention is given to these disorders in neurological practice. The adult‐onset presentation differs from childhood‐onset phenotypes, often leading to considerable diagnostic delay. The identification of these patients at the earliest stage of disease is important, given that early treatment may prevent or lessen further brain damage. Neurological and psychiatric symptoms occur more frequently in adult forms. Abnormalities of eye movements are also common and can be the presenting sign. Eye movement disorders can be classified as central or peripheral. Central forms are frequently observed in lysosomal storage disorders, whereas peripheral forms are a key feature of mitochondrial disease. Furthermore, oculogyric crisis is an important feature in disorders affecting dopamine syntheses or transport. Ocular motor disorders are often not reported by the patient, and abnormalities can be easily overlooked in a general examination. In adults with unexplained psychiatric and neurological symptoms, a special focus on examination of eye movements can serve as a relatively simple clinical tool to detect a metabolic disorder. Eye movements can be easily quantified and analyzed with video‐oculography, making them a valuable biomarker for following the natural course of disease or the response to therapies. Here, we review, for the first time, eye movement disorders that can occur in inborn errors of metabolism, with a focus on late‐onset forms. We provide a step‐by‐step overview that will help clinicians to examine and interpret eye movement disorders. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Combining Human and Rodent Genetics to Identify New Analgesics

Most attempts at rational development of new analgesics have failed, in part because chronic pain involves multiple processes that remain poorly understood. To improve translational success, one strategy is to select novel targets for which there is proof of clinical relevance, either genetically through heritable traits, or pharmacologically. Such an approach by definition yields targets with high clinical validity. The biology of these targets can be elucidated in animal models before returning to the patients with a refined therapeutic. For optimal treatment, having biomarkers of drug action available is also a plus. Here we describe a case study in rational drug design: the use of controlled inhibition of peripheral tetrahydrobiopterin (BH4) synthesis to reduce abnormal chronic pain states without altering nociceptive-protective pain. Initially identified in a population of patients with low back pain, the association between BH4 production and chronic pain has been confirmed in more than 12 independent cohorts, through a common haplotype (present in 25% of Caucasians) of the rate-limiting enzyme for BH4 synthesis, GTP cyclohydrolase 1 (GCH1). Genetic tools in mice have demonstrated that both injured sensory neurons and activated macrophages engage increased BH4 synthesis to cause chronic pain. GCH1 is an obligate enzyme for de novo BH4 production. Therefore, inhibiting GCH1 activity eliminates all BH4 production, affecting the synthesis of multiple neurotransmitters and signaling molecules and interfering with physiological function. In contrast, targeting the last enzyme of the BH4 synthesis pathway, sepiapterin reductase (SPR), allows reduction of pathological BH4 production without completely blocking physiological BH4 synthesis. Systemic SPR inhibition in mice has not revealed any safety concerns to date, and available genetic and pharmacologic data suggest similar responses in humans. Finally, because it is present in vivo only when SPR is inhibited, sepiapterin serves as a reliable biomarker of target engagement, allowing potential quantification of drug efficacy. The emerging development of therapeutics that target BH4 synthesis to treat chronic pain illustrates the power of combining human and mouse genetics: human genetic studies for clinical selection of relevant targets, coupled with causality studies in mice, allowing the rational engineering of new analgesics.

An unusual presentation of tyrosine hydroxylase deficiency

Background

Dopa-responsive dystonia (DRD) has largely been associated with autosomal dominant mutations in the GCH1 gene leading to GTP cyclohydrolase 1 deficiency. More recently, a deficiency in tyrosine hydroxylase (TH) has been recognized to cause DRD. This is a rare disorder resulting from genetic mutations in the TH gene on chromosome 11. The phenotype ranges from DRD with complete resolution on levodopa to infantile parkinsonism and encephalopathy only partially responsive to levodopa. Here we discuss an adult with TH deficiency with a history of possible parkinsonism and dystonia responsive to levodopa, notable for a residual dynamic segmental dystonia.

Case presentation

Our patient grew up in rural Myanmar with limited medical care. Childhood was normal except for episodic illness with difficulty moving and speaking. At 18 years he developed difficulty writing. At 21 years he could not speak, walk, or write and was taken to a city hospital. Multiple medications were tried without benefit until he received carbidopa/levodopa, to which he had a miraculous response. Since then he has attempted to come off medication, however after several weeks his symptoms returned. On presentation to us at 31 years he was taking 450 mg levodopa/day and 4 mg trihexyphenidyl/day. He had a dynamic dystonia in his neck and trunk, subtle at rest and prominent with walking. He exhibited a sensory trick when touching his hand to his chin; improvement occurred to a lesser degree when he imagined touching his chin, and to an even lesser degree when the examiner touched his chin. He had no parkinsonism. He underwent genetic testing which revealed a homozygous variant mutation in the TH gene (p.Thr494Met) leading to a diagnosis of autosomal recessive tyrosine hydroxylase deficiency.

Conclusions

TH deficiency can cause a broad range of clinical symptoms and severity. As more cases are discovered, the phenotype expands. Here we describe a unique case of DRD and possible parkinsonism due to TH deficiency with residual symptoms of dystonia that was task dependent and responded to a sensory trick. In addition, while the history is limited, it is possible he may have had episodes similar to "lethargy-irritability crises" seen in more severe cases. In large part he fits within the milder form of TH hydroxylase deficiency.

Nonmotor Symptoms in Dopa-Responsive Dystonia

Background

Dopa-responsive dystonia (DRD) is a rare inherited dystonia, caused by an autosomal dominantly inherited defect in the gene GCH1 that encodes guanosine triphosphate cyclohydrolase 1. It catalyzes the first and rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin, which is the essential co-factor for aromatic amino acid hydroxylases. Mutation results in the typical scenario of a young-onset lower-limb dystonia with diurnal fluctuations, concurrent or subsequent development of parkinsonism and excellent response to levodopa. Given the myriad functions of tetrahydrobiopterin, it is reasonable that other systems, apart from motor, would also be impaired. So far, non-motor symptoms have been overlooked and very few and often contrasting data are currently available on the matter.

Methods

Here by searching the Medline database for publications between 1971 to March 2015, we render an in-depth analysis of all published data on non-motor symptoms in DRD.

Results

Depression and subtle sleep quality impairment have been reported among the different cohorts, while current data do not support any alterations of the cardiologic and autonomic systems. However, there is debate about the occurrence of sleep-related movement disorders and cognitive function. Non-motor symptoms are instead frequently reported among the clinical spectrum of other neurotransmitter disorders which may sometimes mimic DRD phenotype, ie, DRD plus diseases.

Conclusions

Further studies in larger and treatment-naïve cohorts are needed to better elucidate the extend of non-motor symptoms in DRD and also to consider treatment for these.

Genetics of monoamine neurotransmitter disorders

The monoamine neurotransmitter disorders are a heterogeneous group of inherited neurological disorders involving defects in the metabolism of dopamine, norepinephrine, epinephrine and serotonin. The inheritance of these disorders is mostly autosomal recessive. The neurological symptoms are primarily attributable to cerebral deficiency of dopamine, serotonin or both. The clinical presentations were highly variable and substantial overlaps exist. Evidently, laboratory investigations are crucial for accurate diagnosis. Measurement of neurotransmitter metabolites in cerebral spinal fluid (CSF) is the key to delineate the metabolic defects. Adjuvant investigations including plasma phenylalanine, urine pterins, urine 3-O-methyldopa (3-OMD) and serum prolactin are also helpful to establish the diagnosis. Genetic analyses are pivotally important to confirm the diagnosis which allows specific treatments, proper genetic counselling, prognosis prediction, assessment of recurrent risk in the family as well as prenatal diagnosis. Early diagnosis with appropriate treatment is associated with remarkable response and favourable clinical outcome in several disorders in this group.

Combined Sepiapterin Reductase and Methylmalonyl-CoA Epimerase Deficiency in a Second Patient: Cerebrospinal Fluid Polyunsaturated Fatty Acid Level and Follow-Up Under L-DOPA, 5-HTP and BH4 Trials

Objective/context: We describe the second patient presenting the combination of two homoallelic homozygous nonsense mutations in two genes distant from 1.8 Mb in the chromosome 2p13-3, the methylmalonyl-CoA epimerase gene (MCEE) and the sepiapterin reductase gene (SPR).

CASE REPORT

The patient was born from consanguineous parents. He has presented a moderate but constant methylmalonic acid (MMA) excretion in urine associated with a mental retardation. The first homozygous mutation was identified in the MCEE gene (c.139C>T; p.Arg47*). Progressive dystonia and cataplexy narcolepsy led to diagnose the second homozygous mutation in the SPR gene: c.751A>T; p.Lys251*. Sepiapterin reductase deficiency (SRD) was characterized by a defect in tetrahydrobiopterin (BH4), the cofactor of several hydroxylases needed for the synthesis of neurotransmitters. A treatment with L-DOPA/carbidopa and 5-HTP dramatically improved the dystonic posture, the mood and the hypersomnia, proving that the pathogenesis was due to SRD. A supplementation with BH4 did not induce additional clinical benefit, although HVA and HIAA increased in CSF. The polyunsaturated fatty acids were measured in CSF as the markers of the neuronal stress. We have shown that DHA and its precursor EPA were high before and during the time course of the different treatments.

IN CONCLUSION

The patient has inherited two copies of the two mutations from his consanguineous parents in the MCEE and SPR genes in the chromosome 2p13-3. DHA and EPA increased in CSF as a response to the neuronal stress induced by the defect in neurotransmitters or the altered metabolism of the odd-chain fatty acids and cholesterol.