Nonmotor Symptoms in Dopa-Responsive Dystonia

Segawa Syndrome, a Dramatic Response to Dopamine

Segawa syndrome usually manifests as dystonia, disturbance of gait with fatigue, and may be confused with spasticity. Also known as dopamine-responsive dystonia (DRD), it should be considered in any child who presents with paroxysmal or progressive hypertonia of unknown etiology, which responds dramatically to levodopa. It is a clinical diagnosis, but the level of pterins in cerebrospinal fluid and guanosine triphosphate cyclohydrolase-1 (GTCH 1) gene mutation testing done by molecular genetic testing are confirmatory. Our case is a 45-year female with a family history of similar illness expressed as autosomal recessive inheritance pattern. She had symptoms onset at an early age of 13 years with features of dystonia of predominantly lower limbs, hence the inability to maintain posture and walk. Dramatic improvement with levodopa but sudden deterioration to dystonia due to noncompliance was evident in our patient with troublesome features of concomitant adjustment disorder during presentation.

GTP cyclohydroxylase1 (GCH1): Role in neurodegenerative diseases

GCH1 gene provides directions for the synthesis of GTP cyclohydrolase 1 which regulates the formation of Tetrahydrobiopterin (BH4). BH4 is a crucial cofactor for essential neurotransmitters synthesis such as dopamine, serotonin and nitric oxide synthases. Deficiency of GCH1 limits the synthesis of BH4 which is responsible for neuropsychiatric diseases such as dopa-responsive dystonia, hyperalaninemia, Parkinson's disease and depression. Few single nucleotide polymorphisms of GCH1 gene are also responsible for pain in sickle cell disease. Furthermore, GCH1 regulates NO activity which controls the blood pressure, vasodilatory functions and oxidative stress. Understanding the therapeutic implications of targeting GCH1 which holds promise for treating various diseases. Novel therapeutic strategies could involve small molecule drugs or gene therapy techniques that enhance GCH1 expression or activity.

Neuropsychiatric and sleep study in autosomal dominant dopa-responsive dystonia

Introduction

Although the diurnal fluctuation of motor dysfunction, reversible with small doses of dopamine, is a cornerstone for the phenotype of the autosomal dominant Segawa syndrome, the non-motor symptoms of this neurotransmitter deficiency have still received limited attention.

Objective

This study aims to evaluate non-motor symptoms of this dopa-responsive dystonia through an intrafamilial comparative cross-sectional study.

Methods

Seventeen individuals with a c.IVS5 + 3insT (c.626 + 3insT) variation in the GTP cyclohydrolase-1 gene (GCH1, HGNC: 4193) and 34 intrafamilial controls were studied using the Beck Depression Inventory-II, the Wiener Matrizen Test 2, the Epworth Sleepiness Scale, the Pittsburgh Sleep Quality Index, the MINI/MINI PLUS Questionnaires, the World Health Organization Quality of Life – BREF Instrument and a drug use assessment questionnaire.

Results

No significant difference was found between the groups in the prevalence of sleep disorders and in cognitive function. Nevertheless, generalized anxiety disorder (p = 0.050) and attention-deficit/hyperactivity disorder in childhood (p = 0.011) were observed only in individuals without the molecular variation. The group with the GCH1 variation presented a worse perception about how safe they feel in their daily lives (p = 0.034), less satisfaction with themselves (p = 0.049) and with their relationships (p = 0.029), and a higher prevalence of past major depressive episodes before use of L-Dopa (p = 0.046).

Conclusion

Low dopamine could have been protective against generalized anxiety disorder and attention-deficit/hyperactivity disorder in childhood in Segawa group individuals. The prevalence of depression was higher in individuals with the molecular variant prior to the L-Dopa treatment. Considering it, the penetrance estimates for the variant carriers increased from 58.8% to up to 88% in this large studied family. Additionally, neuropsychiatric tests of all individuals with a molecular diagnosis in an affected family are a valuable instrument for its clinical management.

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Depression can be a non-motor symptom of autosomal dominant DYT/PARK-GCH1.

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Variable expressivity and penetrance can be considered high in this syndrome.

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Relatives without dystonia should also be investigated for the genetic variation.

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.

Longitudinal evaluations of somatosensory-motor inhibition in Dopa-responsive dystonia

INTRODUCTION

GCH1 mutations have been linked to decreased striatal dopamine and development of dopa-responsive dystonia (DRD) and Parkinsonism. Sensory and sensorimotor integration impairments have been documented in various forms of dystonia. DRD patients with confirmed GCH1 mutations have demonstrated normal short-latency afferent inhibition (SAI), a measure of sensorimotor inhibition, under chronic dopaminergic replacement therapy (DRT), but reduced inhibition after a single l-dopa dose following 24 h withdrawal. Studies have revealed normal SAI in other forms of dystonia but reductions with DRT in Parkinson's disease. Longitudinal changes in sensorimotor inhibition are unknown.

METHODS

We analyzed sensorimotor inhibition using two different measures: SAI and somatosensory-motor inhibition using dual-site transcranial magnetic stimulation (ds-TMS). SAI was measured using digit stimulation 25 ms prior to contralateral primary motor cortex (M1) TMS. DS-TMS was measured using TMS over the somatosensory cortex 1 or 2.5 ms prior to ipsilateral M1 stimulation. A total of 20 GCH1 mutation carriers and 20 age-matched controls were included in the study. SAI and ds-TMS were evaluated in GCH1 mutation carriers both OFF and ON DRT compared to controls. Furthermore, longitudinal changes of SAI were examined in a subset of the same individuals that were measured ∼five years earlier.

RESULTS

Neither SAI nor ds-TMS were significantly different in GCH1 mutation carriers relative to controls. No effects of DRT on SAI or ds-TMS were seen but SAI decreased over time in mutation carriers OFF DRT.

CONCLUSION

Our longitudinal results suggest changes in SAI that could be associated with plasticity changes in sensorimotor networks.

Personalized Medicine to Improve Treatment of Dopa-Responsive Dystonia-A Focus on Tyrosine Hydroxylase Deficiency

Dopa-responsive dystonia (DRD) is a rare movement disorder associated with defective dopamine synthesis. This impairment may be due to the fact of a deficiency in GTP cyclohydrolase I (GTPCHI, GCH1 gene), sepiapterin reductase (SR), tyrosine hydroxylase (TH), or 6-pyruvoyl tetrahydrobiopterin synthase (PTPS) enzyme functions. Mutations in GCH1 are most frequent, whereas fewer cases have been reported for individual SR-, PTP synthase-, and TH deficiencies. Although termed DRD, a subset of patients responds poorly to L-DOPA. As this is regularly observed in severe cases of TH deficiency (THD), there is an urgent demand for more adequate or personalized treatment options. TH is a key enzyme that catalyzes the rate-limiting step in catecholamine biosynthesis, and THD patients often present with complex and variable phenotypes, which results in frequent misdiagnosis and lack of appropriate treatment. In this expert opinion review, we focus on THD pathophysiology and ongoing efforts to develop novel therapeutics for this rare disorder. We also describe how different modeling approaches can be used to improve genotype to phenotype predictions and to develop in silico testing of treatment strategies. We further discuss the current status of mathematical modeling of catecholamine synthesis and how such models can be used together with biochemical data to improve treatment of DRD patients.