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

A Young Woman With Hypertonia, Severe Scoliosis, and Encephalopathy

A 31-year-old woman was seen with contractures in her fingers and toes, carpal inversion, dysarthria, dysphagia, hypertonia, decreased tendon reflexes, absence of Babinski sign, and no psychiatric problems and significant global atrophy. What is your diagnosis?

Segawa syndrome caused by TH gene mutation and its mechanism

Dopa-responsive dystonia (DRD), also known as Segawa syndrome, is a rare neurotransmitter disease. The decrease in dopamine caused by tyrosine hydroxylase (TH) gene mutation may lead to dystonia, tremor and severe encephalopathy in children. Although the disease caused by recessive genetic mutation of the tyrosine hydroxylase (TH) gene is rare, we found that the clinical manifestations of seven children with tyrosine hydroxylase gene mutations are similar to dopa-responsive dystonia. To explore the clinical manifestations and possible pathogenesis of the disease, we analyzed the clinical data of seven patients. Next-generation sequencing showed that the TH gene mutation in three children was a reported homozygous mutation (c.698G>A). At the same time, two new mutations of the TH gene were found in other children: c.316_317insCGT, and c.832G>A (p.Ala278Thr). We collected venous blood from four patients with Segawa syndrome and their parents for real-time quantitative polymerase chain reaction analysis of TH gene expression. We predicted the structure and function of proteins on the missense mutation iterative thread assembly refinement (I-TASSER) server and studied the conservation of protein mutation sites. Combined with molecular biology experiments and related literature analysis, the qPCR results of two patients showed that the expression of the TH gene was lower than that in 10 normal controls, and the expression of the TH gene of one mother was lower than the average expression level. We speculated that mutation in the TH gene may clinically manifest by affecting the production of dopamine and catecholamine downstream, which enriches the gene pool of Segawa syndrome. At the same time, the application of levodopa is helpful to the study, diagnosis and treatment of Segawa syndrome.

A Clinical and Integrated Genetic Study of Isolated and Combined Dystonia in Taiwan

Dystonia is a clinically and genetically heterogeneous movement disorder. However, genetic causes of dystonia remain largely unknown in Asian subjects. To address this, we applied an integrated two-step approach that included gene dosage analysis and a next-generation sequencing panel containing 72 known genes causative for dystonia and related movement disorders to 318 Taiwanese patients with isolated or combined dystonia. Whole-genome sequencing was performed for one multiplex family with no known causative variant. The panel confirmed the genetic diagnosis in 40 probands (12.6%). A genetic diagnosis was more likely with juvenile onset compared with adult onset (24.2% vs 10.8%; P = 0.03) and those with combined features, especially with myoclonus, compared with isolated dystonia (35.3% vs 10.5%; P = 0.004). The most common causative genes were SGCE followed by GCH1, TH, CACNA1B, PRRT2, MR1, CIZ1, PLA2G6, and PRKN. Genetic causes were identified from single cases in TOR1A, TUBB4A, THAP1, ATP1A3, ANO3, GNAL, KMT2B, SLC6A3, ADCY5, CYP27A1, PANK2, C19orf12, and SPG11. The whole-genome sequencing analysis identified a novel intragenic deletion in OPHN1 in a multiplex family with X-linked dystonia and intellectual delay. Our findings delineate the genetic architecture and clinical spectrum of dystonia-causing pathogenic variants in an Asian population.

Ending diagnostic odyssey using clinical whole-exome sequencing (CWES)

Objectives

Most rare diseases are genetic diseases. Due to the diversity of rare diseases and the high likelihood of patients with rare diseases to be undiagnosed or misdiagnosed, it is not unusual that these patients undergo a long diagnostic odyssey before they receive a definitive diagnosis. This situation presents a clear need to set up a dedicated clinical service to end the diagnostic odyssey of patients with rare diseases.

Methods

Therefore, in 2014, we started an Undiagnosed Diseases Program in Hong Kong with the aim of ending the diagnostic odyssey of patients and families with rare diseases by clinical whole-exome sequencing (CWES), who have not received a definitive diagnosis after extensive investigation.

Results

In this program, we have shown that genetic diseases diagnosed by CWES were different from that using traditional approaches indicating that CWES is an essential tool to diagnose rare diseases and ending diagnostic odysseys. In addition, we identified several novel genes responsible for monogenic diseases. These include the TOP2B gene for autism spectrum disorder, the DTYMK gene for severe cerebral atrophy, the KIF13A gene for a new mosaic ectodermal syndrome associated with hypomelanosis of Ito, and the CDC25B gene for a new syndrome of cardiomyopathy and endocrinopathy.

Conclusions

With the incorporation of CWES in an Undiagnosed Diseases Program, we have ended diagnostic odysseys of patients with rare diseases in Hong Kong in the past 7 years. In this program, we have shown that CWES is an essential tool to end diagnostic odysseys. With the declining cost of next-generation sequencers and reagents, CWES set-ups are now affordable for clinical laboratories. Indeed, owing to the increasing availability of CWES and treatment modalities for rare diseases, precedence can be given to both common and rare medical conditions.

Compound heterozygous mutations in the TH gene in a Chinese family with autosomal-recessive dopa-responsive dystonia: A case report

RATIONALE

Autosomal-recessive dopa-responsive dystonia (DRD) is a rare clinical disorder presenting as bradykinesia, dystonia, tremor and even severe encephalopathy, and caused by tyrosine hydroxylase deficiency (THD). We report a case of compound heterozygous mutations in the TH gene in a Chinese family with autosomal-recessive DRD herein.

PATIENT CONCERNS

A 16-month-old Chinese boy presented with symptoms of movement disorder and growth retardation in his infant period.

DIAGNOSES

The genetic test revealed compound heterozygous mutations in the TH gene at c.457C>T and c.698G>A, which are pathogenic of DRD.

INTERVENTIONS

The patient was administrated low-dose levodopa.

OUTCOMES

The treatment resulted in the substantial improvement of dystonia. His long-term neurological outcome need follow-up for years.

LESSONS

Gene mutation analysis is helpful and necessary to diagnose DRD and has important guiding significance for the subsequent treatment.

Dopa-Responsive Dystonia in Han Chinese Patients: One Novel Heterozygous Mutation in GTP Cyclohydrolase 1 (GCH1) and Three Known Mutations in TH

Background

This study aimed to clarify the diagnosis and expand the understanding of dopa-responsive dystonia (DRD).

Material/Methods

Relevant data from clinical diagnoses and genetic mutational analyses in 3 Han Chinese patients with sporadic DRD were collected and analyzed. Protein structure/function was predicted.

Results

One novel mutation of c.679A>G (p.T227A) in GCH1 and 3 known mutations of c.457C>T (p.R153X), c.739G>A (p.G247S), and c.698G>A (p.R227H) in tyrosine hydroxylase (TH) have been found and predicted to be damaging or deleterious. All of the mutations were localized in conserved sequences. The iterative threading assembly refinement (I-TASSER) server generated three-dimensional (3D) atomic models based on protein sequences from the novel nonsense mutation of c.679A>G (p.T227A) in GCH1, which showed that residue 227 was located in the GCH1 active site.

Conclusions

Patients carrying different non-synonymous variants had remarkable variation in clinical phenotype. This study expands the spectrum of genotypes and phenotypes of DRD in the Han Chinese ethnicity, provides new insights into the molecular mechanism of DRD, and helps the diagnosis and treatment of DRD.

Monoamine neurotransmitter disorders--clinical advances and future perspectives

The monoamine neurotransmitter disorders are important genetic syndromes that cause disturbances in catecholamine (dopamine, noradrenaline and adrenaline) and serotonin homeostasis. These disorders result in aberrant monoamine synthesis, metabolism and transport. The clinical phenotypes are predominantly neurological, and symptoms resemble other childhood neurological disorders, such as dystonic or dyskinetic cerebral palsy, hypoxic ischaemic encephalopathy and movement disorders. As a consequence, monoamine neurotransmitter disorders are under-recognized and often misdiagnosed. The diagnosis of monoamine neurotransmitter disorders requires detailed clinical assessment, cerebrospinal fluid neurotransmitter analysis and further supportive diagnostic investigations. Prompt and accurate diagnosis of neurotransmitter disorders is paramount, as many are responsive to treatment. The treatment is usually mechanism-based, with the aim to reverse disturbances of monoamine synthesis and/or metabolism. Therapeutic intervention can lead to complete resolution of motor symptoms in some conditions, and considerably improve quality of life in others. In this Review, we discuss the clinical features, diagnosis and management of monoamine neurotransmitter disorders, and consider novel concepts, the latest advances in research and future prospects for therapy.

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.

Prevalence of inherited neurotransmitter disorders in patients with movement disorders and epilepsy: a retrospective cohort study

BACKGROUND

Inherited neurotransmitter disorders are primary defects of neurotransmitter metabolism. The main purpose of this retrospective cohort study was to identify prevalence of inherited neurotransmitter disorders.

METHODS

This retrospective cohort study does not have inclusion criteria; rather included all patients who underwent cerebrospinal fluid (CSF) homovanillic and 5-hydroxyindol acetic acid measurements. Patients with CSF neurotransmitter investigations suggestive of an inherited neurotransmitter disorder and patients with normal or non-diagnostic CSF neurotransmitter investigations underwent direct sequencing of single gene disorders.

RESULTS

There were 154 patients between October 2004 and July 2013. Four patients were excluded due to their diagnosis prior to this study dates. Two major clinical feature categories of patients who underwent lumbar puncture were movement disorders or epilepsy in our institution. Twenty out of the 150 patients (13.3%) were diagnosed with a genetic disorder including inherited neurotransmitter disorders (6 patients) (dihydropteridine reductase, 6-pyruvoyl-tetrahydropterin synthase, guanosine triphosphate cyclohydrolase I, tyrosine hydroxylase, pyridoxine dependent epilepsy due to mutations in the ALDH7A1 gene and pyridoxamine-5-phosphate oxidase deficiencies) and non-neurotransmitter disorders (14 patients).

CONCLUSION

Prevalence of inherited neurotransmitter disorders was 4% in our retrospective cohort study. Eight out of the 150 patients (5.3%) had one of the treatable inherited metabolic disorders with favorable short-term neurodevelopmental outcomes, highlighting the importance of an early and specific diagnosis. Whole exome or genome sequencing might shed light to unravel underlying genetic defects of new inherited neurotransmitter disorders in near future.

Functional studies of tyrosine hydroxylase missense variants reveal distinct patterns of molecular defects in Dopa-responsive dystonia

Congenital tyrosine hydroxylase deficiency (THD) is found in autosomal-recessive Dopa-responsive dystonia and related neurological syndromes. The clinical manifestations of THD are variable, ranging from early-onset lethal disease to mild Parkinson disease-like symptoms appearing in adolescence. Until 2014, approximately 70 THD patients with a total of 40 different disease-related missense mutations, five nonsense mutations, and three mutations in the promoter region of the tyrosine hydroxylase (TH) gene have been reported. We collected clinical and biochemical data in the literature for all variants, and also generated mutant forms of TH variants previously not studied (N = 23). We compared the in vitro solubility, thermal stability, and kinetic properties of the TH variants to determine the cause(s) of their impaired enzyme activity, and found great heterogeneity in all these properties among the mutated forms. Some TH variants had specific kinetic anomalies and phenylalanine hydroxylase, and Dopa oxidase activities were measured for variants that showed signs of altered substrate binding. p.Arg233His, p.Gly247Ser, and p.Phe375Leu had shifted substrate specificity from tyrosine to phenylalanine and Dopa, whereas p.Cys359Phe had an impaired activity toward these substrates. The new data about pathogenic mechanisms presented are expected to contribute to develop individualized therapy for THD patients.

Tyrosine hydroxylase deficiency in Taiwanese infants

We analyzed the clinical manifestations, genetic mutations, treatment responses to L-dopa, and long-term neurologic outcomes in Taiwanese infants with tyrosine hydroxylase deficiency. From 1999 to May 2011, we enrolled six infants who had been diagnosed with tyrosine hydroxylase deficiency by identifying point mutations on the tyrosine hydroxylase gene. Two patients manifested fetal distress during the perinatal period. Four patients exhibited generalized tremor as their first observed neurologic sign at age 3 months. All presented brisk reflexes, hypokinesia, rigidity, distal chorea, and athetosis. We identified a novel missense mutation, I382T, and report on the first patient, to the best of our knowledge, with a homozygous R153X nonsense mutation. Five of six patients responded to L-dopa at a dose of 4.2-34.7 mg/kg/day combined with biperiden or selegiline or both. Long-term neurologic outcomes (median follow-up, 5 years and 10.5 months) revealed two patients demonstrated slightly low intelligence quotients, three demonstrated mild to moderate psychomotor retardation, and one died of respiratory failure. A higher dose of L-dopa, together with alternative therapies, may lead to improvements in motor function. However, several years of observation may be needed to reach definitive conclusions about neurologic outcomes.

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.