Long-term course of L-dopa-responsive dystonia caused by tyrosine hydroxylase deficiency

Experimental pharmacology: Targeting metabolic pathways

Since the discovery of the treatment for Wilson disease a growing number of treatable inherited dystonias have been identified and their search and treatment have progressively been implemented in the clinics of patients with dystonia. While waiting for gene therapy to be more widely and adequately translated into the clinical setting, the efforts to divert the natural course of dystonia reside in unveiling its pathogenesis. Specific metabolic treatments can rewrite the natural history of the disease by preventing neurotoxic metabolite accumulation or interfering with the cell accumulation of damaging metabolites, restoring energetic cell fuel, supplementing defective metabolites, and supplementing the defective enzyme. A metabolic derangement of cell homeostasis is part of the progression of many non-metabolic genetic lesions and could be the target for possible metabolic approaches. In this chapter, we provided an update on treatment strategies for treatable inherited dystonias and an overview of genetic dystonias with new experimental therapeutic approaches available or close to clinical translation.

Diagnosis of autism in a rare case of tyrosine hydroxylase deficiency: a case report

BACKGROUND

Tyrosine hydroxylase deficiency (THD) is a rare movement disorder with broad phenotypic expression caused by bi-allelic mutations in the TH gene, which encode for tyrosine hydroxylase (TH) protein. Some patients with THD have improvement in dystonia with carbidopa-levodopa, a synthetic form of dopamine typically used in Parkinson's disease, and are considered to have dopa-responsive THD. THD has been found in 0.5-1 per million persons, although due to overlapping symptoms with other disorders and the need for genetic testing, prevalence is likely underestimated. Existing literature describes some patients with THD having intellectual disability, but comorbid autism spectrum disorder (ASD) has not been reported.

CASE PRESENTATION

A nearly 3-year-old boy was referred to pediatric neurology due to hypotonia, delayed motor milestones, and expressive speech delay. Whole exome sequencing confirmed tyrosine hydroxylase deficiency, detecting a novel variant p.S307C first reported here. The child was treated with carbidopa-levodopa with an excellent response, resulting in improved balance, fewer falls, and improved ability to jump, run and climb stairs. He was determined to have dopa-responsive THD. Due to his delays in expressive speech, the boy also had an assessment with a developmental and behavioral pediatrician, who identified a pattern of social pragmatic speech delay, sensory sensitivities, and restricted interests, and determined that he met criteria for a diagnosis of ASD.

CONCLUSIONS

While ASD can stand alone as a clinical diagnosis, it is also a cardinal feature of other genetically-based neurological disorders. To our knowledge, this is the first case that describes a patient with both disorders. Perhaps THD may be among the genetic disorders linked with ASD.

A case of treatable encephalopathy, developmental regression, and proximal tremor

Tyrosine hydroxylase (TH) deficiency is an autosomal recessive condition first described as a progressive, early-onset hypokinetic-rigid and dystonic syndrome that was responsive to levodopa. Here we present a child with developmental regression, proximal tremor, and encephalopathy found to have tyrosine hydroxylase deficiency in whom treatment resulted in acquisition of developmental milestones.

Dopa-responsive dystonia, DRD-plus and DRD look-alike: a pragmatic review

Dopa-responsive dystonia (DRD) and DRD plus are diseases of the dopamine pathway with sizeable genetic diversity and myriad presentations. DRD has onset in childhood or adolescence with focal dystonia, commonly affecting lower limb, diurnal fluctuations with evening worsening of symptoms and a demonstrable sleep benefit. DRD "plus" has "atypical features" which include infantile onset, psychomotor delay, cognitive abnormalities, oculogyric crisis, seizures, irritability, spasticity, hypotonia, ptosis, hyperthermia and cerebellar dysfunction. Neurodegeneration, however, is not a feature of either DRD or DRD-plus disorders. Tetrahydrobiopterin (BH4), a key cofactor, deficiency leads to inadequate dopamine and serotonin synthesis. Norepinephrine deficiency may coexist, depending on the enzyme defect. Hyperphenylalaninemia (HPA) is a clue for BH4 paucity. However, HPA is conspicuously absent in autosomal-dominant guanosine triphosphate cyclohydrolase 1 deficiency and sepiapterin reductase deficiency. DRD look-alike is a group of neurodegenerative disorders involving the nigrostriatal dopaminergic system, which could present with dystonia responsive to dopaminergic drugs or neurodegenerative or non-neurodegenerative disorders without involving the nigrostriatal dopaminergic system yet responsive to levodopa. Although levodopa is the mainstay of therapy, response to this drug can be unsatisfactory in DRD plus and DRD look-alike and other drugs are tried. Simultaneous management of HPA leads to remarkable improvement in both motor and cognitive functions. The aim of this review is to help neurology practitioners in treating patients with DRD, DRD-plus and DRD look-alike as many of them have excellent outcome with appropriate therapy.

Identification of TH Variants in Chinese Dopa-Responsive Dystonia Patients and Long-Term Outcomes

Background: Dopa-responsive dystonia (DRD) is a movement disorder that is highly clinically and genetically heterogeneous. Our study summarizes clinical characteristics and long-term outcomes in patients with dopa-responsive dystonia with the aim of obtaining further knowledge on this disorder.

Methods: Patients who met DRD genetic diagnostic criteria through whole-exome sequencing and took levodopa for over 3 years were included in our study. Detailed information was collected on these patients, including family history, age at onset, age and dosage at starting levodopa, current medication and dosage, levodopa duration, diurnal fluctuation, and other clinical features. The Burke–Fahn–Marsden Dystonia Rating Scale-Motor (BFMDRS-M) score was used to evaluate patients' dystonia and variation after levodopa. According to the long-term outcomes, patients were further graded as good (dystonia improved by more than 50% after levodopa, and no further motor symptoms appeared) and poor (dystonia improved by <50% after levodopa, or new motor symptoms appeared).

Results: A total of 20 DRD patients were included (11 with GCH1 variants, 9 with TH variants). During long-term levodopa treatment, three patients with TH variants (3/20, 15%) developed motor symptoms, including body jerks and paroxysmal symptoms, and responded well to increasing levodopa doses. The patient with homozygous mutation c.1481C>T/p. Thr494Met harbored more serious symptoms and poor response to levodopa and showed decreased cardiac uptake in MIBG.

Conclusions: Most DRD patients showed satisfactory treatment outcomes after long-term levodopa, whereas few patients with TH variants presented motor symptoms, which is considered to be related to dopamine insufficiency. For patients with motor symptoms after long-term levodopa, increasing the dose slowly might be helpful to relieve symptoms.

Dystonia and leveraging oral pharmacotherapy

Dystonia is a clinically diverse disorder, characterized by sustained or intermittent muscle contractions causing abnormal and often repetitive movements and/or postures. Accurate clinical diagnosis is tantamount to effective dystonia management. Current guidelines in the treatments of dystonia, including oral therapy, are prescribed to improve symptoms and to restore functional capacity. Identifying treatable causes from co-existing phenomenologies is relevant to provide the most optimal and disease-specific medications. In other forms of dystonia, genetic factors may affect outcome. Moreover, proper selection of patients, early initiation of medications and customized drug titration are keys to increasing the chances of success when using oral therapies for dystonia. Treatment of dystonia primarily involves agents that target dopamine and acetylcholine receptors. Other drugs used include benzodiazepines, baclofen, antiepileptics, some antipsychotics drugs and antihistamine, with different levels of evidence of effectiveness. Unfortunately, most of the widely used drugs have low levels of evidence and are primarily based on anecdotal experiences. Finally, other adjunctive therapeutic strategies are often necessary to complement oral therapy.

Dopa-responsive dystonia caused by tyrosine hydroxylase deficiency: Three cases report and literature review

RATIONAL

Tyrosine hydroxylase deficiency (THD) is a rare cause of dopa-responsive dystonia (DRD). Although the symptoms of DRD may be improved by treatment with L-dopa, the low morbidity of THD can lead to its misdiagnosis. Thus, it is important for physicians to be aware of THD as a cause of DRD.

PATIENT CONCERNS

We report 3 cases of THD. A 5-year-old boy with DRD was diagnosed with THD and found to have compound heterozygous mutations of the TH gene, including TH:c.647G>C from his mother and TH:c.646G>A from his father. Two female siblings also were found to have TH:c.698G>A from their mother and TH:c.710T>C from their father. The younger daughter, at age 3.5 years, was diagnosed with DRD caused by THD, and then the diagnosis of the older daughter, at age 11 years, was changed from cerebral palsy to DRD caused by THD.

DIAGNOSIS

The diagnosis of dopa-responsive dystonia caused by tyrosine hydroxylase deficiency was determined by whole exome sequencing.

INTERVENTION

They all treated with low dose levodopa and benserazide tablets.

OUTCOMES

The boy had a very good therapeutic effect, and he could walk very well by the second day of treatment. The younger sister of the siblings had a partial therapeutic effect, but her elder sister was only little effective with a milder improvement of dystonia and improvement of myodynamia.

CONCLUSION

The characteristics of THD are heterogeneous, and its phenotypes are classified as type A or type B according to increasing severity. Generally, L-dopa has a good therapeutic effect in cases with type A phenotypes. We reviewed 87 cases of reported in the literature and found that c.698G>A and c.707T>C are hot spot mutations. Changes on cerebral magnetic resonance imaging were nonspecific. Analysis of neurotransmitter levels in cerebrospinal fluid is an invasive means of achieving a biochemical diagnosis.

Movement Disorders in Inherited Metabolic Diseases in Children

Movement disorders are one of the important neurological manifestations of inherited metabolic disorders. Important clues to the presence of an underlying inborn error of metabolism are early onset, presence of neuroregression or degeneration, parental consanguinity, sibling affection, paroxysmal events, waxing and waning course, skin or hair changes, absence of a perinatal insult or any structural cause, and presence of identifiable triggers. It is particularly important to recognize this class of movement disorders as several of them are eminently treatable and may often need disease-specific therapy besides symptomatic treatment. The current review focusses on the movement disorders associated with inherited metabolic defects in children, with emphasis on treatable disorders.

Clinical and Genetic Heterogeneity in a Cohort of Chinese Children With Dopa-Responsive Dystonia

Background: The aim of this study was to investigate the genetic and clinical features of dopa-responsive dystonia (DRD) in China. Method: Characteristics of gene mutations and clinical manifestations of 31 patients diagnosed with DRD were analyzed retrospectively. Result: From January 2000 to January 2019, 31 patients were diagnosed with DRD. Twenty (64.5%) were male, and 11 (35.5%) were female. Ten patients (32.3%) had classic DRD, 19 (61.3%) had DRD-plus, and 2 (6.4%) patients had mutations in the dopamine synthetic pathway (PTS gene mutation) without a typical phenotype (not DRD or DRD-plus). Twenty-eight (90.3%) patients underwent genetic testing. Homozygous or compound heterozygous TH gene mutations were found in 22 patients. GCH1 and PTS gene mutations were found in 2 patients. Heterozygous TH mutation and genetic testing were negative in 1 patient. They took different doses of L-dopa, ranging from 0.4 to 8.7 mg/kg/d. Patients with classic DRD responded well. In patients with DRD-plus, 94.7% (18/19) responded well with residual symptoms. One patient (5.3%) did not show any improvement. Conclusion: DRD can be divided into classic DRD and DRD-plus. In this cohort, the most common pathogenic gene was TH. Fever was the important inducing factor of the disease. L-dopa has sustained and stable effects on patients with classic DRD. In patients with DRD-plus, treatment with L-dopa could ameliorate most of the symptoms.

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.

Movement Disorders and Neurometabolic Diseases

Many inherited metabolic diseases or inborn errors of metabolism (IEM) cause movement disorders in children. This review focuses on chorea, dystonia, myoclonus, tremor, and parkinsonism. Broad neurometabolic categories commonly responsible for pediatric movement disorders include mitochondrial cytopathies, organic acidemias, mineral metabolism and transport disorders, neurotransmitter diseases, purine metabolism abnormalities, lipid storage conditions, and creatine metabolism dysfunction. Each movement disorder can be caused by many IEM and several of them can cause multiple movement abnormalities. Dietary modifications, medications, and increasingly specific therapy can improve outcomes in children with movement disorders caused by IEM. Recognition and characterization of secondary movement disorders in children facilitate their management and diagnosis, and possible treatment of an underlying IEM.

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.

An Indian Family with Tyrosine Hydroxylase Deficiency

BACKGROUND

Tyrosine Hydroxylase deficiency is a rare neurotransmitter disorder.

CASE CHARACTERISTICS

An Indian family with the disorder.

OBSERVATIONS

Phenotypic variation, elevated serum prolactin, genetic confirmation, and partial treatment-responsiveness.

MESSAGE

Tyrosine Hydroxylase deficiency is a treatable inborn error of metabolism and serum prolactin assists in diagnosis.

A novel tyrosine hydroxylase variant in a group of Chinese patients with dopa-responsive dystonia

Dopa-responsive dystonia (DRD) comprises a heterogeneous group of movement disorders. A limited number of studies of Chinese patients with DRD have been reported. In the present study, we investigated the clinical and genetic features of 12 Chinese DRD families. Point mutation analysis of the GTP-cyclohydrolase I (GCH1), tyrosine hydroxylase (TH) and sepiapterin reductase (SPR) genes was conducted by direct sequencing. In addition, multiplex ligation-dependent probe amplification targeting GCH1 and TH was performed in "mutation-free" patients. Three reported mutations (IVS2-2A>G, c.293C>T, c.550C>T) were detected in GCH1, whereas two compound heterozygous variants were identified in TH, one of which was novel (c.1083C>A). Furthermore, this novel variant was not detected in any of the 250 ethnicity-matched, healthy controls. No exon deletions or duplicate mutations in the two genes were found in patients with DRD. No mutation in SPR was found. In addition, one patient with the IVS2-2A>G mutation in GCH1 showed signs of Parkinsonism. In conclusion, we here identified a novel heterozygous variant in TH (c.1083C>A). It is important to perform routine screening of GCH1 and TH for patients with DRD. While for patients with Parkinsonism, GCH1 mutation analysis should be performed after screening of genes like PARKIN, PARK7 (DJ-1) and PINK1.

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.

Cerebrospinal fluid synaptic proteins as useful biomarkers in tyrosine hydroxylase deficiency

Tyrosine hydroxylase (TH) deficiency is an inborn error of dopamine biosynthesis and a cause of early parkinsonism. Two clinical phenotypes have been described. Type "B": early onset severe encephalopathy; type "A": later onset, less severe and better response to L-dopa. We aimed to study the expression of several key dopaminergic and gabaergic synaptic proteins in the cerebrospinal fluid (CSF) of a series of patients with TH deficiency and their possible relation with the clinical phenotype and response to L-DOPA. Dopamine transporter (DAT), D2-receptor and vesicular monoamine transporter (VMAT2) were measured in the CSF of 10 subjects with TH deficiency by Western blot analysis. In 3 patients, data of pre- and post-treatment with L-DOPA were available, and in one of them, GABA vesicular transporter was determined. Results were compared to an age-matched control population. The concentration of D2-receptors in CSF was significantly higher in patients with TH deficiency than in controls. Similarly, DAT and vesicular monoamine transporter type 2 were up-regulated. Studies performed before L-DOPA, and on L-DOPA therapy showed a paradoxical response with D2 receptor expression increase as L-Dopa doses and homovanillic concentration gradually raised in a B phenotype patient. The opposite results were found in two patients with A phenotype. However, this is a very small sample, and further studies are needed to conclude robust differences between phenotypes. Synaptic proteins are detectable in the CSF and their quantification can be useful for understanding the pathophysiology of neurotransmitter defects and potentially to adjust and personalize treatments in the future.

Effects of Tyrosine on Parkinson's Disease: A Randomized, Double-Blind, Placebo-Controlled Trial

Individuals with Parkinson's disease (PD) can suffer from orthostatic hypotension (OH) resulting from reduced levels of norepinephrine (NE), which inhibits the sympathetic nervous system. Levodopa reduces NE levels even further, leading to a greater decrease in blood pressure (BP) and increased OH. Tyrosine is a nonessential amino acid that is the major precursor to NE. Reduced levels of tyrosine have been shown after administration of l-dopa. This study was a single-center, randomized, double-blind, placebo-controlled trial to test the effects of supplementing l-tyrosine on BP, plasma tyrosine, NE levels, and autonomic responses to exercise in PD. Thirty-six subjects with PD receiving l-dopa medication that suffer from OH participated. Random assignment was to a placebo group or l-tyrosine 1,000 mg (500 mg of 2× daily) group for 7 days. OH testing and exercise testing was performed pre- and postsupplementation. There was no effect of tyrosine on BP after OH testing postsupplementation (tyrosine, n = 17; placebo, n = 19). There was an increase in plasma tyrosine in the tyrosine group (P > 0.05). There were no significant changes in any of the secondary outcome measures. l-tyrosine at 1,000 mg (500 mg/2× day) for 7 days is safe and well tolerated in PD. Our results were inconclusive as to whether an increase in plasma tyrosine has an effect on OH in subjects with PD. An increase in plasma tyrosine had no effect on BP or autonomic responses in subjects with PD during acute exercise stress. (Trial registration: http://ClinicalTrials.gov.; identifier: NCT01676103).

Clinical spectrum of dopa-responsive dystonia and related disorders

Dopa-responsive dystonia (DRD) has a classic presentation of childhood or adolescent-onset dystonia, mild parkinsonism, marked diurnal fluctuations, improvement with sleep or rest, and a dramatic and sustained response to low doses of L-dopa without motor fluctuations or dyskinesias. However, there have been many papers on patients with a wide range of features, which report them as DRD mainly because they had dystonic syndromes with L-dopa responsiveness. Many mutations in the dopaminergic system have been found as molecular genetic defects. Therefore, the clinical and genetic spectra of DRD are unclear, which lead to difficulties in diagnostic work-ups and planning treatments. We propose the concept of DRD and DRD-plus to clarify the confusion in this area and to help understand the pathophysiology and clinical features, which will help in guiding diagnostic investigations and planning treatments. We critically reviewed the literature on atypical cases and discussed the limitations of the gene study.

Treatable inborn errors of metabolism causing neurological symptoms in adults

BACKGROUND

The identification of inborn errors of metabolism (IEM) in adults presenting with a wide range of neurological symptoms is a relatively new field in medicine. We sought to identify which treatable IEM have been diagnosed for the first time in adults and generate a protocol for metabolic screening targeting those treatable disorders.

METHODS

Medline/Pubmed searches of English language literature limited to the adult age group were performed. Diseases identified through this search were then compared to previously published lists of treatable IEM in both adults and children.

RESULTS

85% of the treatable conditions known to cause global developmental delay or intellectual disability in children had reports where the diagnosis of that IEM was made in one or more adult patients with neurological symptoms. Screening tests in blood, urine, CSF and MRI can detect most of these treatable conditions but the diagnostic accuracy of these screening tests in adults is not clear.

CONCLUSION

Treatable IEM need to be considered in the differential diagnosis of neurological symptoms in patients of any age.

A new tyrosine hydroxylase genotype associated with early-onset severe encephalopathy

We describe a boy affected by an early-onset severe encephalopathy (stagnation of psychomotor development, paroxysmal dystonic postures and movements of limbs, hypokinesia) due to tyrosine hydroxylase deficiency. High blood prolactin and low homovanillic acid in cerebrospinal fluid suggested the diagnosis. Genetic analysis revealed 3 new missense mutations on tyrosine hydroxylase gene: [c.752C>T(p.P251L) and c.887G>A(p.R296Q] harbored by the father and c.836G>T (p.C279F) of maternal origin. Bioinformatics tools have been helpful in predicting the pathogenic role of p.P251L and p.C279F substitutions, while a weak pathogenic effect was ascribed to p.R296Q.

Age-related medical decision limits for urinary free (unconjugated) metadrenalines, catecholamines and metabolites in random urine specimens from children

Background

Neuroblastoma is the most common extracranial solid tumour in childhood (8% of all childhood cancers), the most frequently diagnosed in infancy, and has one of the highest death rates, while chromaffin tumours rarely present in childhood. Both tumour types produce catecholamines and their metabolites. It is difficult to produce reference ranges for tests in children, and currently, no age-related medical decision limits for free metadrenalines (free metanephrines) in random urine specimens exist in the paediatric literature.

Methods

Results of vanillylmandelic acid (VMA), 5-hydroxyindoleacetic acid, homovanillic acid (HVA), noradrenaline (NA), adrenaline, dopamine (DA), free normetadrenaline (fNMA), free metadrenaline and free 3-methoxytyramine (f3MT) in 1658 random urines obtained from infants, children and young adults were measured by high performance liquid chromatography with electrochemical detection. Specimens were excluded from consideration if obtained from the following categories, i.e. (a) harbouring neuroblastic, chromaffin, carcinoid or other tumours or malignancies; (b) medical conditions having known association with excess catecholamine excretion; (c) patients administered catecholamine or paracetamol; (d) overly dilute urine; and (e) manifesting outlying values following visual inspection.

Results

There remained 872 specimens that were grouped into seven age ranges (<1; 1 or 2; 3 or 4; 5–7; 8–10; 11–13; 14–19 y) for which medical decision limits were determined for each analyte. There was no significant difference between the results for boys or girls. In 55 patients harbouring neuroblastic tumours, HVA (54/55), f3MT (14/16), VMA (45/53) and DA (43/53) were the most frequently elevated analytes at time of diagnosis. In 11 patients presenting in childhood with chromaffin tumours, fNMA (11/11) followed by NA (10/11) were the most frequently elevated.

Discussion

The likely reasons for outlying or missing values, together with the reasons for variation in the distinctive biochemical patterns of analytes exhibited in individuals harbouring either neuroblastic or chromaffin tumours are discussed.

Bilateral subthalamic nucleus deep brain stimulation for dopa-responsive dystonia in a 6-year-old child

Tyrosine hydroxylase (TH) deficiency is a rare autosomal recessive metabolic disease that results in the decreased production of catecholamines. Standard treatment relies on combinations of levodopa and carbidopa, anticholinergic agents, serotonergic agonists, and monamine oxidase B inhibitors. Unfortunately, severely affected children often require escalating doses of medication and suffer from dyskinesias as well as significant on/off symptomatology. The authors present a case of medically intractable dopa-responsive dystonia in a 6-year-old boy whose condition significantly improved with bilateral subthalamic nucleus deep brain stimulation. This case is unique in its novel approach to tyrosine hydroxylase deficiency and the young age of the patient.

Increase of BM-MSC proliferation using L-DOPA on titanium surface in vitro

In order to increase biocompatibility, many dental implants have been studied by immobilization of biomolecules on biomaterials. We used l-3,4-dihydroxyphenylalanine (L-DOPA) as a biomolecule for surface-modified titanium. Water contact angles of nontreated titanium discs (negative control), etched titanium discs (positive control), and titanium discs treated with L-DOPA following the etching process (experimental group) were 82.4 ± 5.7°, 67.1 ± 0.56°, and 44.15 ± 0.91°, respectively. Using atomic force microscopy images, we were able to find L-DOPA, which adhered to the titanium surface. The number of human bone marrow mesenchymal stem cells (BM-MSCs) in the experimental group was much higher than that of cells in any other group. Quantification values of amine groups in the positive control and experimental groups were approximately 3 and 7.5 µg, respectively. Therefore, findings from our research suggested the possibility of a causal link between increased L-DOPA content and cell proliferation in BM-MSCs. Moreover, coating of the discs with L-DOPA can result in greater hydrophilicity of the titanium surface and enhancement of cell adhesion and mitochondrial activity.

Expanding phenotype and clinical analysis of tyrosine hydroxylase deficiency

This study included 12 Chinese patients with a wide spectrum of phenotypes of tyrosine hydroxylase deficiency. Seven females and 5 males, aged 2.2 to 41 years, had phenotypes ranging from severe type with onset at infancy to mild type with onset after 3 years of age. Patients with the severe type had encephalopathy with poor treatment response or infantile parkinsonism with motor delay. Patients with the less common mild type had dopa-responsive dystonia or a newly recognized predominant symptom of myopathy. Female siblings had more severe phenotypes. The phenotype and treatment outcomes were strongly related to a homovanillic acid level and homovanillic acid/5-hydroxyindolacetic acid ratio of less than 1 in the cerebrospinal fluid. Hyperprolactinemia was found in 50% of the severe cases. Levodopa was the mainstay of treatment, and early addition of selegiline resulted in a remarkable response in some patients. Treatment response for mild-type patients is universally good even with a treatment delay of 10 years after onset of neurological symptoms.

Movement disorders in neuro-metabolic diseases

Inborn errors of metabolism (IEM) are a group of genetic disorders characterized by dysfunction of an enzyme or other protein involved in cellular metabolism.(1) Most IEMs involve the nervous system (neuro-metabolic diseases or NMD). NMD often present with a complex clinical picture: psychomotor retardation and/or regression, pyramidal signs, ataxia, hypotonia and epilepsy and movement disorders.(1) Movement disorders are more frequently part of this complex picture than a predominant symptom, however in some instances the clinical picture may be summarized in an invalidating movement disorder.(2) On a phenomenology basis, one can distinguish eight main types of movement disorders: dystonia and athetosis, chorea, tremor with or without parkinsonism, ballismus, myoclonus, tics and stereotypies. Most of these abnormal involuntary movements generate from a dysfunction or a lesion in the basal ganglia, excepting myoclonus, the origin of which can vary (cortical, brainstem, basal ganglia, spinal and even peripheral nervous system).(3) Classically the most frequently observed movement disorders in NMD are: dystonia, myoclonus, chorea, tremor and parkinsonism (Fig. 1). The primary goal of this article is, departing from the literature and a large personal series, to describe the types of movement disorders most frequently observed in NMD and to discuss their clinical value in the setting of specific types of NMD.

Marked improvement in Segawa syndrome after L-dopa and selegiline treatment

Three brothers, born to parents who were first cousins, were referred for progressive diffuse dystonia. Initial physical examinations revealed minor dysmorphic features, e.g., bifrontal narrowing, downslanting palpebral fissures, low-set ears, upturned nostrils, and microretrognathia, as well as neurodevelopmental delay. Absence of eye contact and head control, diffuse dystonia, hypokinesia, choreoathetosis, tremor, increased deep tendon reflexes, diffuse muscle atrophy, and spasticity were evident during neurologic evaluations. After laboratory investigations, imaging studies, and the exclusion of other causes of childhood dystonia, the children were diagnosed with Segawa syndrome. A molecular analysis of the tyrosine hydroxylase gene revealed a novel P492R (1475 C>G) mutation, further confirming the clinical diagnosis. After 1-month therapy with 2 mg/kg/day l-dopa, no changes in signs were evident. Selegiline was added, which greatly improved the clinical picture. Segawa syndrome in three brothers resulted from a novel mutation in the tyrosine hydroxylase gene. Treatment with a combination of l-dopa and selegiline led to favorable outcomes.

Biochemical and molecular characterization of tyrosine hydroxylase deficiency in Hong Kong Chinese

Tyrosine hydroxylase deficiency is a rare neurotransmitter disorder affecting the rate-limiting step in catecholamine biosynthesis. There are about 40 cases reported worldwide. Here, we report the biochemical and molecular findings of eight unrelated Chinese patients with tyrosine hydroxylase deficiency. We have identified eight novel mutations with 5 missense, 2 nonsense and 1 splicing mutations in the TH gene, namely p.R153X, p.R169X, p.G294R, p.G315S, p.A385V, p.I394T, p.G408R, and c.1163+5G>C. The mutations of the TH gene in Chinese are heterogeneous.

Exhaustive analysis of BH4 and dopamine biosynthesis genes in patients with Dopa-responsive dystonia

Dopa-responsive dystonia is a childhood-onset dystonic disorder, characterized by a dramatic response to low dose of L-Dopa. Dopa-responsive dystonia is mostly caused by autosomal dominant mutations in the GCH1 gene (GTP cyclohydrolase1) and more rarely by autosomal recessive mutations in the TH (tyrosine hydroxylase) or SPR (sepiapterin reductase) genes. In addition, mutations in the PARK2 gene (parkin) which causes autosomal recessive juvenile parkinsonism may present as Dopa-responsive dystonia. In order to evaluate the relative frequency of the mutations in these genes, but also in the genes involved in the biosynthesis and recycling of BH4, and to evaluate the associated clinical spectrum, we have studied a large series of index patients (n = 64) with Dopa-responsive dystonia, in whom dystonia improved by at least 50% after L-Dopa treatment. Fifty seven of these patients were classified as pure Dopa-responsive dystonia and seven as Dopa-responsive dystonia-plus syndromes. All patients were screened for point mutations and large rearrangements in the GCH1 gene, followed by sequencing of the TH and SPR genes, then PTS (pyruvoyl tetrahydropterin synthase), PCBD (pterin-4a-carbinolamine dehydratase), QDPR (dihydropteridin reductase) and PARK2 (parkin) genes. We identified 34 different heterozygous point mutations in 40 patients, and six different large deletions in seven patients in the GCH1 gene. Except for one patient with mental retardation and a large deletion of 2.3 Mb encompassing 10 genes, all patients had stereotyped clinical features, characterized by pure Dopa-responsive dystonia with onset in the lower limbs and an excellent response to low doses of L-Dopa. Dystonia started in the first decade of life in 40 patients (85%) and before the age of 1 year in one patient (2.2%). Three of the 17 negative GCH1 patients had mutations in the TH gene, two in the SPR gene and one in the PARK2 gene. No mutations in the three genes involved in the biosynthesis and recycling of BH4 were identified. The clinical presentations of patients with mutations in TH and SPR genes were strikingly more complex, characterized by mental retardation, oculogyric crises and parkinsonism and they were all classified as Dopa-responsive dystonia-plus syndromes. Patient with mutation in the PARK2 gene had Dopa-responsive dystonia with a good improvement with L-Dopa, similar to Dopa-responsive dystonia secondary to GCH1 mutations. Although the yield of mutations exceeds 80% in pure Dopa-responsive dystonia and Dopa-responsive dystonia-plus syndromes groups, the genes involved are clearly different: GCH1 in the former and TH and SPR in the later.

Neuroimaging findings in children with paediatric neurotransmitter diseases

Paediatric neurotransmitter diseases consist of a group of inherited neurometabolic diseases in children, and include disorders related to gamma-amino butyric acid (GABA) metabolism, monoamine biosynthesis, etc. The diagnosis of paediatric neurotransmitter diseases remain a great challenge for paediatricians and child neurologists. In addition to clinical manifestations and CSF neurotransmitter measurement, neuroimaging findings can also be very informative for the diagnosis and evaluation of the patients. For patients with monoamine biosynthesis disorders, the functional evaluation of dopaminergic transmission also plays an important role. Understanding of the possible neuroimaging changes in paediatric neurotransmitter diseases is therefore of great value for the investigation of these patients.

Mutations in human monoamine-related neurotransmitter pathway genes

Biosynthesis and metabolism of serotonin and catecholamines involve at least eight individual enzymes that are mainly expressed in tissues derived from the neuroectoderm, e.g., the central nervous system (CNS), pineal gland, adrenal medulla, enterochromaffin tissue, sympathetic nerves, and ganglia. Some of the enzymes appear to have additional biological functions and are also expressed in the heart and various other internal organs. The biosynthetic enzymes are tyrosine hydroxylase (TH), tryptophan hydroxylases type 1 and 2 (TPH1, TPH2), aromatic amino acid decarboxylase (AADC), dopamine beta-hydroxylase (DbetaH), and phenylethanolamine N-methyltransferase (PNMT), and the specific catabolic enzymes are monoamine oxidase A (MAO-A) and catechol O-methyltransferase (COMT). For the TH, DDC, DBH, and MAOA genes, many single nucleotide polymorphisms (SNPs) with unknown function, and small but increasing numbers of cases with autosomal recessive mutations have been recognized. For the remaining genes (TPH1, TPH2, PNMT, and COMT) several different genetic markers have been suggested to be associated with regulation of mood, pain perception, and aggression, as well as psychiatric disturbances such as schizophrenia, depression, suicidality, and attention deficit/hyperactivity disorder. The genetic markers may either have a functional role of their own, or be closely linked to other unknown functional variants. In the future, molecular testing may become important for the diagnosis of such conditions. Here we present an overview on mutations and polymorphisms in the group of genes encoding monoamine neurotransmitter metabolizing enzymes. At the same time we propose a unified nomenclature for the nucleic acid aberrations in these genes. New variations or details on mutations will be updated in the Pediatric Neurotransmitter Disorder Data Base (PNDDB) database (www.bioPKU.org).

Movement disorders and inborn errors of metabolism in adults: a diagnostic approach

Inborn errors of metabolism (IEMs) may present in adolescence or adulthood with various movement disorders including parkinsonism, dystonia, chorea, tics or myoclonus. Main diseases causing movement disorders are metal-storage diseases, neurotransmitter synthesis defects, energy metabolism disorders and lysosomal storage diseases. IEMs should not be missed as many are treatable. Here we briefly review IEMs causing movement disorders in adolescence and adults and propose a simple diagnostic approach to guide metabolic investigations based on the clinical course of symptoms, the type of abnormal movements, and brain MRI abnormalities.

Subthalamic nucleus stimulation for primary dystonia and tardive dystonia

With the renaissance of stereotactic pallidotomy for Parkinson's disease in 1990s, pallidotomy has become increasingly used as an effective treatment for various manifestations of medically refractory dystonia. More recently, deep brain stimulation of globus pallidus internus (GPi) has been replacing pallidotomy. Although GPi DBS has great promise for treating dystonia, there are some disadvantages. We introduce our experiences in subthalamic nucleus (STN) DBS for primary dystonia and tardive dystonia in this chapter. We propose that STN DBS has the following advantages over GPi DBS: (1) symptomatic improvement is seen immediately after stimulation, allowing us to quickly select the most suitable stimulation parameters; (2) the stimulation parameters for the STN are lower than those used for the GPi, resulting in longer battery life; and (3) STN DBS results in better symptomatic control than GPi DBS in dystonia patients when our STN data is compared to that obtained by others with using the GPi as the target. We suggest that STN DBS may be the most appropriate surgical technique for dystonia.

Hereditary spastic paraparesis in adults associated with inborn errors of metabolism: a diagnostic approach

Spastic paraparesis is a general term describing progressive stiffness and weakness in the lower limbs caused by pyramidal tract lesions. This clinical situation is frequently encountered in adult neurology. The diagnostic survey is usually limited to searching for acquired causes (spinal cord compression, inflammatory, metabolic, infectious diseases) and the so-called 'hereditary spastic paraparesis'. Although poorly recognized by neurologists, spastic paraparesis is also one of the multiple presentations of inborn errors of metabolism (IEMs) in children and adults. Pyramidal signs are usually included in a diffuse neurological or systemic clinical picture; however, in some cases spastic paraparesis remains the only symptom for years. Since these metabolic causes are often treatable, it is essential to include them in the general diagnostic approach to spastic paraparesis. Here we review IEMs causing paraparesis in adults.

Therapy insight: inborn errors of metabolism in adult neurology--a clinical approach focused on treatable diseases

Inborn errors of metabolism (IEMs) are genetic disorders characterized by dysfunction of an enzyme or other protein involved in cellular metabolism. In most cases, IEMs involve the nervous system. The first clinical symptoms of IEMs usually present in infancy, but in an unknown proportion of cases they can appear in adolescence or adulthood. In this Review, we focus on treatable IEMs, presenting acutely or chronically, that can be diagnosed in an adult neurology department. To make our presentation readily usable by clinicians, the Review is subdivided into eight sections according to the main clinical presentations: emergencies (acute encephalopathies and strokes), movement disorders, peripheral neuropathies, spastic paraparesis, cerebellar ataxia, psychiatric disorders, epilepsy and leukoencephalopathies. Our aim is to present simple guidelines to enable neurologists to avoid overlooking a treatable metabolic disease.

Galactorrhea-a strong clinical clue towards the diagnosis of neurotransmitter disease

Two siblings from a Hong Kong Chinese family are diagnosed to have heterozygous mutation in tyrosine hydroxylase gene-a novel mutation R169X and the common Dutch mutation R233H. Presented with developmental delay and dystonia before 6 months of age, both had hyperprolactinemia with persistent galactorrhea present in the elder brother since birth. Serum prolactin level is a good screening test for those suspected of underlying neurotransmitter diseases. To our knowledge, this is the first Chinese family diagnosed with such condition. Clinicians must be aware of this rare disease especially in those unexplained 'cerebral palsy' like children.