Levodopa-responsive dystonia. GTP cyclohydrolase I or parkin mutations?

Parkinsonism originates in a discrete secondary and dystonia in a primary motor cortical-basal ganglia subcircuit

Although manifesting contrasting phenotypes, Parkinson's disease and dystonia, the two most common movement disorders, can originate from similar pathophysiology. Previously, we demonstrated that lesioning (silencing) of a discrete dorsal region in the globus pallidus (rodent equivalent to globus pallidus externa) in rats and produced parkinsonism, while lesioning a nearby ventral hotspot-induced dystonia. Presently, we injected fluorescent-tagged multi-synaptic tracers into these pallidal hotspots (n = 36 Long Evans rats) and permitted 4 days for the viruses to travel along restricted connecting pathways and reach the motor cortex before sacrificing the animals. Viral injections in the Parkinson's hotspot fluorescent labeled a circumscribed region in the secondary motor cortex, while injections in the dystonia hotspot labeled within the primary motor cortex. Custom probability mapping and N200 staining affirmed the segregation of the cortical territories for Parkinsonism and dystonia to the secondary and primary motor cortices. Intracortical microstimulation localized territories specifically to their respective rostral and caudal microexcitable zones. Parkinsonian features are thus explained by pathological signaling within a secondary motor subcircuit normally responsible for initiation and scaling of movement, while dystonia is explained by abnormal (and excessive) basal ganglia signaling directed at primary motor corticospinal transmission.

The Functional Meaning of 5'UTR in Protein-Coding Genes

As it is well known, messenger RNA has many regulatory regions along its sequence length. One of them is the 5' untranslated region (5'UTR), which itself contains many regulatory elements such as upstream ORFs (uORFs), internal ribosome entry sites (IRESs), microRNA binding sites, and structural components involved in the regulation of mRNA stability, pre-mRNA splicing, and translation initiation. Activation of the alternative, more upstream transcription start site leads to an extension of 5'UTR. One of the consequences of 5'UTRs extension may be head-to-head gene overlap. This review describes elements in 5'UTR of protein-coding transcripts and the functional significance of protein-coding genes 5' overlap with implications for transcription, translation, and disease.

Parkinsonism in Genetic Neurodevelopmental Disorders: A Systematic Review

Background

With advances in clinical genetic testing, associations between genetic neurodevelopmental disorders and parkinsonism are increasingly recognized. In this review, we aimed to provide a comprehensive overview of reports on parkinsonism in genetic neurodevelopmental disorders and summarize findings related to genetic diagnosis, clinical features and proposed disease mechanisms.

Methods

A systematic literature review was conducted in PubMed and Embase on June 15, 2021. Search terms for parkinsonism and genetic neurodevelopmental disorders, using generic terms and the Human Phenotype Ontology, were combined. Study characteristics and descriptive data were extracted from the articles using a modified version of the Cochrane Consumers and Communication Review Group's data extraction template. The protocol was registered in PROSPERO (CRD42020191035).

Results

The literature search yielded 208 reports for data-extraction, describing 69 genetic disorders in 422 patients. The five most reported from most to least frequent were: 22q11.2 deletion syndrome, beta-propeller protein-associated neurodegeneration, Down syndrome, cerebrotendinous xanthomatosis, and Rett syndrome. Notable findings were an almost equal male to female ratio, an early median age of motor onset (26 years old) and rigidity being more common than rest tremor. Results of dopaminergic imaging and response to antiparkinsonian medication often supported the neurodegenerative nature of parkinsonism. Moreover, neuropathology results showed neuronal loss in the majority of cases. Proposed disease mechanisms included aberrant mitochondrial function and disruptions in neurotransmitter metabolism, endosomal trafficking, and the autophagic-lysosomal and ubiquitin-proteasome system.

Conclusion

Parkinsonism has been reported in many GNDs. Findings from this study may provide clues for further research and improve management of patients with GNDs and/or parkinsonism.

Levodopa-responsive dystonia caused by biallelic PRKN exon inversion invisible to exome sequencing

Biallelic pathogenic variants in PRKN (PARK2), encoding the E3 ubiquitin ligase parkin, lead to early-onset Parkinson's disease. Structural variants, including duplications or deletions, are common in PRKN due to their location within the fragile site FRA6E. These variants are readily detectable by copy number variation analysis. We studied four siblings with levodopa-responsive dystonia by exome sequencing followed by genome sequencing. Affected individuals developed juvenile levodopa-responsive dystonia with subsequent appearance of parkinsonism and motor fluctuations that improved by subthalamic stimulation. Exome sequencing and copy number variation analysis were not diagnostic, yet revealed a shared homozygous block including PRKN. Genome sequencing revealed an inversion within PRKN, with intronic breakpoints flanking exon 5. Breakpoint junction analysis implicated non-homologous end joining and possibly replicative mechanisms as the repair pathways involved. Analysis of cDNA indicated skipping of exon 5 (84 bp) that was replaced by 93 bp of retained intronic sequence, preserving the reading frame yet altering a significant number of residues. Balanced copy number inversions in PRKN are associated with a severe phenotype. Such structural variants, undetected by exome analysis and by copy number variation analysis, should be considered in the relevant clinical setting. These findings raise the possibility that PRKN structural variants are more common than currently estimated.

Case Report: Guitarist's cramp as the initial manifestation of dopa-responsive dystonia with a novel heterozygous GCH1 mutation

Dopa-responsive dystonia (DRD), also known as Segawa syndrome, is a phenotypically and genetically heterogeneous group of neurological disorders that typically presents as early-onset lower limb dystonia with diurnal fluctuation, and exhibits a marked, persistent response to levodopa. Heterozygous loss-of-function mutations in the guanosine triphosphate cyclohydrolase 1 (GCH1) are the most common cause of DRD. In addition to the classic form of the disease, there have been a number of studies addressing atypical clinical features of GCH1 related DRD with variable age of onset. This report describes a 37-year-old Japanese male patient with a 10-year history of focal upper limb dystonia that initially emerged as task-specific, guitarist’s cramp. The dystonic symptoms responded very well to levodopa treatment, and genetic analysis identified a novel heterozygous mutation in the C-terminal catalytic domain of GCH1. Insufficient recognition of this treatable condition often leads to misdiagnosis, which causes delays in the patient receiving adequate dopamine replenishing therapy. A diagnostic trial with levodopa should be considered in all patients with relatively young-onset dystonia, whether they have classic features of DRD or not.

Early-onset autosomal dominant GTP-cyclohydrolase I deficiency: Diagnostic delay and residual motor signs

OBJECTIVE

Autosomal dominant (AD) guanosine triphosphate cyclohydrolase 1 (GCH1) deficiency is the most common cause of dopa-responsive dystonia (DRD). Patients with GCH1 deficiency are likely to experience diagnostic delay, but its consequences have not been described thoroughly in patients with early-onset disease. We describe the diagnostic delay and residual motor signs (RMS) observed in patients with early-onset (before 15 years of age) disease.

METHODS

Twelve patients with early-onset AD GCH1 deficiency from a single center were included in the case series analysis. For the meta-analysis, the PubMed database was searched for articles on early-onset AD GCH1 deficiency published from 1995 to 2019.

RESULTS

In the case series, the mean duration of diagnostic delay was 5.6 years. Two patients exhibited RMS, and four patients underwent orthopedic surgery. The literature search yielded 137 AD GCH1 deficiency cases for review; gait disturbance was reported in 92.7% of patients, diurnal fluctuation of symptoms in 91.9%, and RMS in 39%. The mean duration of diagnostic delay was 14.6 years overall: 12.0 years in RMS-negative patients and 21.2 years in RMS-positive patients.

CONCLUSIONS

Diagnostic delay in early-onset AD GCH1 deficiency is more closely associated with later RMS. Early clinical suspicion, timely diagnosis, and levodopa treatment may reduce the occurrence of RMS in patients with early-onset AD GCH1 deficiency.

Series of Dopa Responsive Dystonia Masquerading as Other Diseases with Short Review

Dopa-responsive dystonia (DRD) encompasses a group of clinically and genetically heterogeneous disorders that typically manifest as limb-onset, diurnally fluctuating dystonia presenting in early life and exhibits a robust and sustained response to levodopa treatment. DRD is one of the treatable dystonia syndromes of childhood. It starts with the involvement of lower limb and associated with characteristic diurnal variation. Many times it is misdiagnosed as cerebral palsy due to selective lower limb preference. We report a series of three cases of DRD which were previously misdiagnosed. The first case presented as myelopathy and other two were diagnosed as cerebral palsy. It is a treatable condition with very good response to drugs. Early diagnosis and adequate therapy can prevent from catastrophic complications.

A Han Chinese Family With Early-Onset Parkinson's Disease Carrying Novel Frameshift Mutation and Compound Heterozygous Mutation of PRKN Appearing Incompatible With MDS Clinical Diagnostic Criteria

Around 15% of patients with Parkinson's disease (PD) have a family history, and 5–10% have confirmed genetic causes. PRKN is the most common gene responsible for early-onset Parkinson's disease (EOPD), while rare variants of PLA2G6 likely raise PD susceptibility in the Chinese population. We investigated the genetic information of 13 members of a Han Chinese family with known EOPD by whole-exome sequencing and Sanger sequencing, and analyzed the clinical history, physical examination, blood laboratory test, and brain imaging data of the patients. Two members, including the proband, were suspected of having EOPD. A novel homozygous frameshift mutation, c.856delT, and a compound heterozygous mutation, c.1321T>C/c.856delT of PRKN, were identified, as well as two single nucleotide variants of PLA2G6 and TENM4. The proband exhibited a rare symmetrical resting tremor limited to her lower limbs and never exhibited signs of rigidity. ¹⁸F-DOPA PET/CT scan indicated a symmetrical reduced signaling in the striatum. The novel frameshift mutation and compound heterozygous mutation of PRKN are likely to be the genetic causes of EOPD in this family.

Whole exome sequencing identified a new compound heterozygous PRKN mutation in a Chinese family with early-onset Parkinson's disease

Early-onset Parkinson's disease (EOPD) is usually caused by genetic variants and patients with EOPD develop symptoms before the age of 50, accounting for 5% Parkinson's disease (PD). Here we present a Chinese Han pedigree with clinical features of EOPD. To determine the diagnosis and pathogenic mutations of this pedigree, whole exome sequencing, Sanger sequencing and real-time quantitative PCR were performed to detect all the four family members. Our results showed that a new form of compound heterozygous mutation in the PRKN gene, consisting of heterozygous point mutation c.850G > C (p.G284R) along with exon 4 deletion, is the causative genetic factor for EOPD in this pedigree. These discoveries may have implications for genetic counseling, clinical management and developing PRKN target gene therapy strategy.

Juvenile Parkinsonism with PARK2 Gene Mutation Misdiagnosed as Dopa-responsive Dystonia: a Case Report

Parkinson's disease is prevalent in elderly patients, usually aged over 50 years. If clinical symptoms of parkinsonism appear before 21 years of age, it is called juvenile parkinsonism (JP). JP may present atypical features such as dystonia, and is often misdiagnosed as other diseases, including dopa-responsive dystonia (DRD). Here, we report a case of JP with PARK2 mutation misdiagnosed as DRD. A 32-year old female, who presented dystonia of both legs, was initially diagnosed with hereditary spastic paraplegia and showed a dramatic response to low-dose L-dopa, which led to the diagnosis of DRD. However, Parkinson's disease caused by a mutation in the PARK2 gene was later diagnosed via next-generation sequencing. Accurate understanding of JP is necessary for early diagnosis and comprehensive management of movement disorders at a young age.

Autosomal dominant GCH1 mutations causing spastic paraplegia at disease onset

BACKGROUND

Autosomal dominant GCH1 mutations are known to cause dopa-responsive dystonia (DRD). In this case series, we confirm a variant phenotype, characterized by predominant spastic paraplegia at disease onset with development of dystonia and/or parkinsonism only decades later.

METHODS

Clinical trajectories of four patients from three families with pathogenic variants in GCH1 are described, illustrated by videos of the motor phenotype before and during treatment with levodopa. An extensive literature review was performed on previous reports of spasticity in patients with autosomal dominant GCH1 mutations.

RESULTS

All patients presented during childhood or early adolescence with gait and leg spasticity. Three patients developed basal ganglia signs only in the fifth decade; the youngest patient has not yet developed dystonia, bradykinesia or hypokinesia. All patients responded to levodopa/carbidopa with improvement of gait and of dystonia, hypokinesia and/or rigidity. In all patients, spasticity decreased but did not disappear. Spasticity has been described previously in DRD, but in most cases co-existent basal ganglia signs were identified early in the disease course.

CONCLUSION

GCH1 mutations may cause a phenotype initially resembling hereditary spastic paraplegia (HSP) rather than DRD, with basal ganglia signs developing only after decades. In order not to miss this treatable condition, GCH1 should be included in HSP gene panels and its testing is pivotal in patients with spastic paraplegia, especially if there are concomitant basal ganglia signs and/or diurnal fluctuation.

GCH-1 genetic variant may cause Parkinsonism by unmasking the subclinical nigral pathology

BACKGROUND

Recent studies suggest that GTP cyclohydrolase 1 (GCH-1) variant may be a risk factor for nigral degeneration causing PD.

METHODS

A 49-year-old Korean woman visited our movement disorder clinic with the initial presentation of Parkinsonism starting at age 47. We monitored the degree of nigral degeneration with serial FP-CIT PET throughout the course of her disease (2, 8 and 11 years from disease onset).

RESULTS

The initial clinical presentation was consistent with intrinsic dopamine deficiency caused by GCH-1 variant. However, her follow-up disease course was consistent with Parkinsonism caused by nigral neurodegeneration. We found a novel GCH-1 variant in the current case. The disease course of the patient was overall benign in motor and non-motor aspects, corresponding to previously reported GCH-1 cases with PD. Serial FP-CIT PET scans showed normal initial FP-CIT binding followed by a continuous decline of the putaminal binding ratio. However, the decreased binding ratio could not sufficiently explain the corresponding clinical duration of the patient. Therefore, dopamine deficiency by GCH-1 genetic variant contributed to Parkinsonism in the current case with subclinical nigral degeneration.

CONCLUSION

Our case suggests that GCH-1 variant causes Parkinsonism by unmasking the subclinical nigral pathology, not by causing the nigral neurodegeneration.

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.

A Novel Transgenic Mouse Model to Investigate the Cell-Autonomous Effects of torsinA(ΔE) Expression in Striatal Output Neurons

Dystonia is a disabling neurological syndrome characterized by abnormal movements and postures that result from intermittent or sustained involuntary muscle contractions; mutations of DYT1/TOR1A are the most common cause of childhood-onset, generalized, inherited dystonia. Patient and mouse model data strongly support dysregulation of the nigrostriatal dopamine neurotransmission circuit in the presence of the DYT1-causing mutation. To determine striatal medium spiny neuron (MSN) cell-autonomous and non-cell autonomous effects relevant to dopamine transmission, we created a transgenic mouse in which expression of mutant torsinA in forebrain is restricted to MSNs. We assayed electrically evoked and cocaine-enhanced dopamine release and locomotor activity, dopamine uptake, gene expression of dopamine-associated neuropeptides and receptors, and response to the muscarinic cholinergic antagonist, trihexyphenidyl. We found that over-expression of mutant torsinA in MSNs produces complex cell-autonomous and non-cell autonomous alterations in nigrostriatal dopaminergic and intrastriatal cholinergic function, similar to that found in pan-cellular DYT1 mouse models. These data introduce targets for future studies to identify which are causative and which are compensatory in DYT1 dystonia, and thereby aid in defining appropriate therapies.

Current therapies and therapeutic decision making for childhood-onset movement disorders

Movement disorders differ in children to adults. First, neurodevelopmental movement disorders such as tics and stereotypies are more prevalent than parkinsonism, and second, there is a genomic revolution which is now explaining many early-onset dystonic syndromes. We outline an approach to children with movement disorders starting with defining the movement phenomenology, determining the level of functional impairment due to abnormal movements, and screening for comorbid psychiatric conditions and cognitive impairments which often contribute more to disability than the movements themselves. The rapid improvement in our understanding of the etiology of movement disorders has resulted in an increasing focus on precision medicine, targeting treatable conditions and defining modifiable disease processes. We profile some of the key disease-modifying therapies in metabolic, neurotransmitter, inflammatory, and autoimmune conditions and the increasing focus on gene or cellular therapies. When no disease-modifying therapies are possible, symptomatic therapies are often all that is available. These classically target dopaminergic, cholinergic, alpha-adrenergic, or GABAergic neurochemistry. Increasing interest in neuromodulation has highlighted that some clinical syndromes respond better to DBS, and further highlights the importance of "disease-specific" therapies with a future focus on individualized therapies according to the genomic findings or disease pathways that are disrupted. We summarize some pragmatic applications of symptomatic therapies, neuromodulation techniques, and some rehabilitative interventions and provide a contemporary overview of treatment in childhood-onset movement disorders. © 2019 International Parkinson and Movement Disorder Society.

Early Dyskinesias in Parkinson's Disease Patients With Parkin Mutation: A Primary Corticostriatal Synaptopathy?

Mutations in the PARKIN gene cause early-onset Parkinson’s disease (PD). Despite the high proportion of still missing phenotyping data in the literature devoted to early-onset PD, studies suggest that, as compared with late-onset PD, PARKIN patients show dystonia at onset and extremely dose-sensitive levodopa-induced dyskinesia (LID). What pathophysiological mechanisms underpin such early and atypical dyskinesia in patients with PARKIN mutations? Though the precise mechanisms underlying dystonia and LID are still unclear, evidence suggests that hyperkinetic disorders in PD are a behavioral expression of maladaptive functional and morphological changes at corticostriatal synapses induced by long-term dopamine (DA) depletion. However, since the dyskinesia in PARKIN patients can also be present at onset, other mechanisms beside the well-established DA depletion may play a role in the development of dyskinesia in these patients. Because cortical and striatal neurons express parkin protein, and parkin modulates the function of ionotropic glutamatergic receptors (iGluRs), an intriguing explanation may rest on the potential role of parkin in directly controlling the glutamatergic corticostriatal synapse transmission. We discuss the novel theory that loss of parkin function can dysregulate transmission at the corticostriatal synapses where they cause early maladaptive changes that co-occur with the changes stemming from DA loss. This hypothesis suggests an early striatal synaptopathy; it could lay the groundwork for pharmacological treatment of dyskinesias and LID in patients with PARKIN mutations.

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.

De novo tetrahydrobiopterin biosynthesis is impaired in the inflammed striatum of parkin(-/-) mice

Parkinson's disease (PD), the second-most prevalent neurodegenerative disease, is primarily characterized by neurodegeneration in the substantia nigra pars compacta, resulting in motor impairment. Loss-of-function mutations in parkin are the major cause of the early onset familial form of the disease. Although rodents deficient in parkin (parkin(-/-) ) have some dopaminergic system dysfunction associated with central oxidative stress and energy metabolism deficiencies, these animals only display nigrostriatal pathway degeneration under inflammatory conditions. This study investigated the impact of the inflammatory stimulus induced by lypopolisaccharide (LPS) on tetrahydrobiopterin (BH4) synthesizing enzymes (de novo and salvage pathways), since this cofactor is essential for dopamine synthesis. The mitochondrial content and architecture was investigated in the striatum of LPS-exposed parkin(-/-) mice. As expected, the LPS (0.33 mg/kg; i.p.) challenge compromised spontaneous locomotion and social interaction with juvenile parkin(-/-) and WT mice. Moreover, the genotype impacted the kinetics of the investigation of the juvenile. The inflammatory scenario did not induce apparent changes in mitochondrial ultrastructure; however, it increased the quantity of mitochondria, which were of smaller size, and provoked the perinuclear distribution of the organelle. Furthermore, the BH4 de novo biosynthetic pathway failed to be up-regulated in the LPS challenge, a well-known stimulus for its activation. The LPS treatment increased sepiapterin reductase (SPR) expression, suggesting compensation by the salvage pathway. This might indicate that dopamine synthesis is compromised in parkin(-/-) mice under inflammatory conditions. Finally, this scenario impaired the striatal expression of the transcription factor BDNF, possibly favoring cell death.

Neuroinflammation in L-DOPA-induced dyskinesia: beyond the immune function

Neuroinflammation is a main component of Parkinson's disease (PD) neuropathology, where unremitting reactive microglia and microglia-secreted soluble molecules such as cytokines, contribute to the neurodegenerative process as part of an aberrant immune reaction. Besides, pro-inflammatory cytokines, predominantly TNF-α, play an important neuromodulatory role in the healthy and diseased brain, being involved in neurotransmitter metabolism, synaptic scaling and brain plasticity. Recent preclinical studies have evidenced an exacerbated neuroinflammatory reaction in the striatum of parkinsonian rats that developed dyskinetic responses following L-DOPA administration. These findings prompted investigation of non-neuronal mechanisms of L-DOPA-induced dyskinesia (LID) involving glial cells and glial-secreted soluble molecules. Hence, besides the classical mechanisms of LID that include abnormal corticostriatal neurotransmission and maladaptive changes in striatal medium spiny neurons (MSNs), here we review studies supporting a role of striatal neuroinflammation in the development of LID, with a focus on microglia and the pro-inflammatory cytokine TNF-α. Moreover, we discuss several mechanisms that have been involved in the development of LID, which are directly or indirectly under the control of TNF-α, and might be abnormally affected by its chronic overproduction and release by microglia in PD. It is proposed that TNF-α may contribute to the altered neuronal responses occurring in LID by targeting receptor trafficking and function in MSNs, but also dopamine synthesis in preserved dopaminergic terminals and serotonin metabolism in serotonergic neurons. Therapeutic approaches specifically targeting glial-secreted cytokines may represent a novel target for preventing or treating LID.

Atypical presentation of dopa-responsive dystonia in Taiwan

The typical clinical presentation of dopa-responsive dystonia, which is also called Segawa disease, is a young age of onset, with predominance in females, diurnal fluctuation of lower limb dystonia, and fair response to low-dose levodopa. This disease has both autosomal dominant and autosomal recessive inheritance. Autosomal dominant Segawa disease is caused by GCH1 mutation on chromosome 14q22.1-q22.2. Here, we report the case of a male patient with genetically confirmed Segawa disease and atypical presentations including no diurnal symptom fluctuation and insufficient response to levodopa. The patient's father who had the same mutation presented parkinsonism in old age. We also review the literature to address the broad clinical heterogeneity of Segawa disease and the influence of onset age on clinical presentation.

l-Dopa in dystonia

“Every child exhibiting dystonia merits anl-dopa trial, lest the potentially treatable condition of dopa-responsive dystonia (DRD) is missed” has been a commonly cited and highly conserved adage in movement disorders literature stemming from the 1980s. We here provide a historical perspective on this statement, discuss the current diagnostic and therapeutic applications ofl-dopa in everyday neurologic practice, contrast these with its approved indications, and finish with our view on both a diagnostic and therapeutic trial in children and adults with dystonia. In light of the relatively low prevalence of DRDs, the large interindividual variation in the requiredl-dopa dose, the uncertainty about an adequate trial duration, the substantial advances in knowledge on etiology and pathophysiology of these disorders, and the availability of various state-of-the-art diagnostic tests, we think that a diagnosticl-dopa trial as a first step in the approach of early-onset dystonia (≤25 years) is outdated. Rather, in high-resource countries, we suggest to usel-dopa after biochemical corroboration of a defect in dopamine biosynthesis, in genetically confirmed DRD, or if nigrostriatal degeneration has been demonstrated by nuclear imaging in adult patients presenting with lower limb dystonia. Furthermore, our literature study on the effect of a therapeutic trial to gain symptomatic relief revealed thatl-dopa has occasionally proven beneficial in several established “non-DRDs” and may therefore be considered in selected cases of dystonia due to other causes. In summary, we argue against the application ofl-dopa in every patient with early-onset dystonia and support a more rational therapeutic use.

Dopa-responsive dystonia or early-onset Parkinson disease - Genotype-phenotype correlation

OBJECTIVE

Dopa-responsive dystonia (DRD) is a rare form of hereditary movement disorder with onset in childhood, characterized by gait difficulties due to postural dystonia with marked improvement after low doses of levodopa. Mutations in the GCH1 gene are the most common cause of DRD, however, in some cases when the disease is associated with parkinsonism mutations in the PARK2 gene may be identified. The aim of this study was to analyze and compare genotype-phenotype correlation.

MATERIAL/PARTICIPANTS

Four families with inter- and intrafamilial variability of progressive gait dysfunction due to lower limb dystonia occurring in childhood or adolescence were included in the analysis.

METHODS

General and neurological examination was performed for all affected family members and asymptomatic mutation carriers. The molecular analysis encompassed GCH1 and PARK2 genes.

RESULTS

All probands were clinically diagnosed with DRD. The molecular analysis revealed, however, that the dopa-responsive dystonia phenotype was caused by a mutation in the GCH1 gene in three families and in the PARK2 gene in one family. Obtained results allowed to establish the final diagnosis for all families as DYT5a or early-onset Parkinson disease (EO-PD).

CONCLUSIONS

Reported cases confirm that the DRD phenotype may have heterogeneous genetic background and may be caused by point mutations or rearrangements in the GCH1 gene as well as in the PARK2 gene. Differential diagnosis and genetic tests covering the analysis of genes causative for DRD and EO-PD should be obligatory in both disorders diagnostics as DRD, mainly adolescent onset dystonia, may be associated with parkinsonism.

What Is Not in the Name? Dopa-Responsive Dystonia May Respond to More Than L-Dopa

BACKGROUND

Classic L-dopa-responsive dystonia is characterized by the triad of dystonia, diurnal fluctuation of signs, and dramatic response of signs to low-dose L-dopa therapy. Dopa-responsive dystonia succinctly summarizes the relevant clinical features. However, literal application of this label or consideration of dopa-responsive dystonia as a diagnostic end without molecular and/or biochemical definition may contribute to misdiagnosis and incomplete treatment in dopa-responsive conditions that impair synthesis of monoamine neurotransmitters besides dopamine.

PATIENT DESCRIPTION

We describe and provide video for twin patients with a rare form of dopa-responsive dystonia due to sepiapterin reductase deficiency. As is typical in dopa-responsive dystonia, these patients displayed dramatic improvement with L-dopa/carbidopa therapy. However, treatment was suboptimal until 5-hydroxytryptophan was added to address their serotonergic deficit.

DISCUSSION

Our report highlights the limitations of the dopa-responsive dystonia label and increases awareness of sepiapterin reductase deficiency and other conditions that may present as dopa-responsive dystonia. We provide a diagnostic and therapeutic approach to guide the clinician in evaluating and treating individuals with dopa-responsive dystonia.

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.

Progress in unraveling the genetic etiology of Parkinson disease in a genomic era

Parkinson disease (PD) and Parkinson-plus syndromes are genetically heterogeneous neurological diseases. Initial studies into the genetic causes of PD relied on classical molecular genetic approaches in well-documented case families. More recently, these approaches have been combined with exome sequencing and together have identified 15 causal genes. Additionally, genome-wide association studies (GWASs) have discovered over 25 genetic risk factors. Elucidation of the genetic architecture of sporadic and familial parkinsonism, however, has lagged behind that of simple Mendelian conditions, suggesting the existence of features confounding genetic data interpretation. Here we discuss the successes and potential pitfalls of gene discovery in PD and related disorders in the post-genomic era. With an estimated 30% of trait variance currently unexplained, tackling current limitations will further expedite gene discovery and lead to increased application of these genetic insights in molecular diagnostics using gene panel and exome sequencing strategies.

Parkinson's disease in GTP cyclohydrolase 1 mutation carriers

GTP cyclohydrolase 1, encoded by the GCH1 gene, is an essential enzyme for dopamine production in nigrostriatal cells. Loss-of-function mutations in GCH1 result in severe reduction of dopamine synthesis in nigrostriatal cells and are the most common cause of DOPA-responsive dystonia, a rare disease that classically presents in childhood with generalized dystonia and a dramatic long-lasting response to levodopa. We describe clinical, genetic and nigrostriatal dopaminergic imaging ([(123)I]N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl) tropane single photon computed tomography) findings of four unrelated pedigrees with DOPA-responsive dystonia in which pathogenic GCH1 variants were identified in family members with adult-onset parkinsonism. Dopamine transporter imaging was abnormal in all parkinsonian patients, indicating Parkinson's disease-like nigrostriatal dopaminergic denervation. We subsequently explored the possibility that pathogenic GCH1 variants could contribute to the risk of developing Parkinson's disease, even in the absence of a family history for DOPA-responsive dystonia. The frequency of GCH1 variants was evaluated in whole-exome sequencing data of 1318 cases with Parkinson's disease and 5935 control subjects. Combining cases and controls, we identified a total of 11 different heterozygous GCH1 variants, all at low frequency. This list includes four pathogenic variants previously associated with DOPA-responsive dystonia (Q110X, V204I, K224R and M230I) and seven of undetermined clinical relevance (Q110E, T112A, A120S, D134G, I154V, R198Q and G217V). The frequency of GCH1 variants was significantly higher (Fisher's exact test P-value 0.0001) in cases (10/1318 = 0.75%) than in controls (6/5935 = 0.1%; odds ratio 7.5; 95% confidence interval 2.4-25.3). Our results show that rare GCH1 variants are associated with an increased risk for Parkinson's disease. These findings expand the clinical and biological relevance of GTP cycloydrolase 1 deficiency, suggesting that it not only leads to biochemical striatal dopamine depletion and DOPA-responsive dystonia, but also predisposes to nigrostriatal cell loss. Further insight into GCH1-associated pathogenetic mechanisms will shed light on the role of dopamine metabolism in nigral degeneration and Parkinson's disease.

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.

Advances in the Genetics of Parkinson's Disease: A Guide for the Clinician

Over the last 16 years, insights in clinical and genetic characteristics of Parkinson's disease (PD) have increased substantially. We summarize the clinical, genetic, and pathological findings of autosomal dominant PD linked to mutations in SNCA, leucine-rich repeat kinase 2, vacuolar protein sorting-35, and eukaryotic translation initiation factor 4 gamma 1 and autosomal recessive PD linked to parkin,PINK1, and DJ-1, as well as autosomal recessive complicated parkinsonian syndromes caused by mutations in ATP13A2,FBXO7,PLA2G6,SYNJ1, and DNAJC6. We also review the advances in high- and low-risk genetic susceptibility factors and present multisystem disorders that may present with parkinsonism as the major clinical feature and provide recommendations for prioritization of genetic testing. Finally, we consider the challenges of future genetic research in PD.

Dopa-responsive dystonia: functional analysis of single nucleotide substitutions within the 5' untranslated GCH1 region

Background

Mutations in the GCH1 gene are associated with childhood onset, dopa-responsive dystonia (DRD). Correct diagnosis of DRD is crucial, given the potential for complete recovery once treated with L-dopa. The majority of DRD associated mutations lie within the coding region of the GCH1 gene, but three additional single nucleotide sequence substitutions have been reported within the 5’ untranslated (5’UTR) region of the mRNA. The biologic significance of these 5’UTR GCH1 sequence substitutions has not been analyzed.

Methodology/Principal Findings

Luciferase reporter assays, quantitative real time PCR and RNA decay assays, combined with bioinformatics, revealed a pathogenic 5’UTR GCH1 substitution. The +142C>T single nucleotide 5’UTR substitution that segregates with affected status in DRD patients, substantially attenuates translation without altering RNA expression levels or stability. The +142C>T substitution disrupts translation most likely by creating an upstream initiation start codon (uAUG) and an upstream open reading frame (uORF).

Conclusions/Significance

This is the first GCH1 regulatory substitution reported to act at a post-transcriptional level, increasing the list of genetic diseases caused by abnormal translation and reaffirming the importance of investigating potential regulatory substitutions in genetic diseases.

Novel GCH-1 mutations and unusual long-lasting dyskinesias in Korean families with dopa-responsive dystonia

OBJECTIVE

To describe the long-term follow-up data of Korean patients with GTP cyclohydrolase (GTPCH) I deficient dopa-responsive dystonia (DRD) with novel mutations and unusual long-lasting dyskinesias.

METHODS

Clinical features and genetic testing results of GCH1 from 19 patients that included 4 families who have been followed-up for up to 25 years were analyzed.

RESULTS

GCH1 mutations were confirmed in all our symptomatic subjects including 3 novel point mutations. All the subjects except for one family had typical manifestations of autosomal dominant GTPCH-I deficient DRD including early childhood onset dystonia predominantly in the legs, marked diurnal variation, intact cognition, no other systemic symptoms, and excellent sustained response to levodopa. The one family who was the exception had two gene positive members of DRD and one with dopa-unresponsive cervical dystonia with negative GCH1 mutation. One family and a sporadic case had been reported as gene negative in a previous study, but they typically had preserved dopamine transporter binding and low neopterin levels in cerebrospinal fluids; thus, GCH-1 mutation had been highly suspected, which was now confirmed by repeating the genetic testing this time. An early childhood-onset patient developed choreiform dyskinesias right after administration of levodopa. The dyskinesia had lasted for more than 4 years regardless of the levodopa dosages and then subsided while maintaining levodopa.

CONCLUSION

This report emphasizes the usefulness of the neopterin level in cerebrospinal fluids and dopamine transporter imaging in the differential diagnosis of DRD syndromes and a possible mechanism of levodopa-induced-dyskinesia in early childhood onset case.

Gene expression regulation by upstream open reading frames and human disease

Upstream open reading frames (uORFs) are major gene expression regulatory elements. In many eukaryotic mRNAs, one or more uORFs precede the initiation codon of the main coding region. Indeed, several studies have revealed that almost half of human transcripts present uORFs. Very interesting examples have shown that these uORFs can impact gene expression of the downstream main ORF by triggering mRNA decay or by regulating translation. Also, evidence from recent genetic and bioinformatic studies implicates disturbed uORF-mediated translational control in the etiology of many human diseases, including malignancies, metabolic or neurologic disorders, and inherited syndromes. In this review, we will briefly present the mechanisms through which uORFs regulate gene expression and how they can impact on the organism's response to different cell stress conditions. Then, we will emphasize the importance of these structures by illustrating, with specific examples, how disturbed uORF-mediated translational control can be involved in the etiology of human diseases, giving special importance to genotype-phenotype correlations. Identifying and studying more cases of uORF-altering mutations will help us to understand and establish genotype-phenotype associations, leading to advancements in diagnosis, prognosis, and treatment of many human disorders.

The genetics of dystonia: new twists in an old tale

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

Monoamine neurotransmitter deficiencies

Pediatric neurotransmitter disorders refer to a constellation of inherited neurometabolic syndromes attributable to disturbances of neurotransmitter synthesis, degradation, or transport. Monoamine deficiencies represent defects in synthesis of dopamine, serotonin, norepinephrine, and epinephrine or in availability of tetrahydrobiopterin, an important cofactor for monoamine synthesis. Some disorders do not manifest peripheral hyperphenyalaninemia and require CSF neurotransmitter metabolite assay for diagnosis. These include Segawa dopa-responsive dystonia and enzymatic deficiencies of aromatic amino acid decarboxylase, tyrosine hydroxylase, and sepiapterin reductase. The first, autosomal dominantly inherited GTP cyclohydrolase deficiency, has a satisfying response to therapy at any age with benefits maintained over time. The others have more severe and treatment-refractory phenotypes, typically with manifestations well beyond movement disorders. Disorders detectable by elevated serum phenylalanine are deficiencies of GTP cyclohydrolase (homozygous), pterin-carbinolamine dehydratase, dihydropteridine reductase, and pyruvoyl-tetrahydropterin synthase. The latter is the most prevalent and heterogeneous but typically has infantile onset with extrapyramidal as well as bulbar, hypothalamic, limbic, and epileptic manifestations. There are therapeutic roles for neurotransmitter supplementation, and dopaminergic agonists. Basal ganglia calcifications in dihydropteridine reductase deficiency are reversible with folinic acid. Deficiencies of monoamine degradation lead to cognitive, behavioral, and autonomic disorders.

Genetics of Parkinson's disease - a clinical perspective

Discovering genes following Medelian inheritance, such as autosomal dominant-synuclein and leucine-rich repeat kinase 2 gene, or autosomal recessive Parkin, P-TEN-induced putative kinase 1 gene and Daisuke-Junko 1 gene, has provided great insights into the pathogenesis of Parkinson's disease (PD). Genes found to be associated with PD through investigating genetic polymorphisms or via the whole genome association studies suggest that such genes could also contribute to an increased risk of PD in the general population. Some environmental factors have been found to be associated with genetic factors in at-risk patients, further implicating the role of gene-environment interactions in sporadic PD. There may be confusion for clinicians facing rapid progresses of genetic understanding in PD. After a brief review of PD genetics, we will discuss the insight of new genetic discoveries to clinicians, the implications of ethnic differences in PD genetics and the role of genetic testing for general clinicians managing PD patients.

Dyskinesias as a limiting factor in the treatment of Segawa disease

Patients with autosomal dominant Segawa disease (dopa-responsive dystonia) demonstrate excellent, sustained response to low-dose levodopa. In contrast, the development of levodopa limiting treatment dyskinesias is thought to support the diagnosis of other early-onset dystonia/parkinsonism syndromes. We describe an atypical phenotype of persistent treatment limiting dyskinesias in a family with prominent brachial dystonia and a novel GCH1 mutation. The pedigree comprised two affected members: the proband (aged 13 years) and her mildly affected mother (aged 48 years). A phenylalanine loading test, cerebrospinal fluid for biogenic amines and pterins, guanosine triphosphate cyclohydrolase I enzyme activity, and direct exonic sequencing of GCH1 revealed a novel mutation (c.235_240delCTGAGC [p.L79_S80del]) in the GCH1 gene. Despite continuous levodopa therapy from age 7 years, the proband developed severe writer's cramp at age 10 years and persistent treatment limiting dyskinesias, with even low doses of levodopa leading to treatment challenges. Dyskinesias as limiting side effects of levodopa should not preclude a diagnosis of dopa-responsive dystonia during diagnostic levodopa trials. A diagnosis of Segawa disease should still be considered if partial improvement occurs with levodopa, but with dose-limiting dyskinesias.

Occurrence of GCH1 gene mutations in a group of Indian dystonia patients

The aim of this study is to examine the role of GCH1 among Indians affected with dopa responsive dystonia (DRD) and early onset Parkinson's disease (EOPD). The patients (n = 76 including 19 DRD and 36 EOPD) and controls (n = 138) were screened for variants in GCH1 by PCR amplification of exons, splice junctions and 1 kb upstream region followed by SSCP and DNA sequencing. Four novel variants (p.Met1Val, p.Val204_205del, IVS3+68A>G, and IVS5-6T>G) were identified in 10 patients but not in the controls. In addition to two nonsynonymous changes, identified in four DRD patients in heterozygous condition, one intronic variant (IVS5-6T>G) could be linked to pathogenesis of the disease since it has the potential of altering the splice site as assessed by in silico analysis. Patients carrying different nonsynonymous variants had remarkable variation in clinical phenotype. Consistent with earlier reports, severity of clinical phenotype and the age of onset varied among family members harboring the same mutation. No mutation was detected in the EOPD patients. Three novel mutations in GCH1 gene have been found and are shown to be associated with variable clinical phenotypes mostly within the spectrum of DRD. The mutations identified represent 15.79% (3/19) of east Indian DRD patient cohort.

Tyrosine nitration of PA700 links proteasome activation to endothelial dysfunction in mouse models with cardiovascular risk factors

Oxidative stress is believed to cause endothelial dysfunction, an early event and a hallmark in cardiovascular diseases (CVD) including hypertension, diabetes, and dyslipidemia. However, the targets for oxidative stress-mediated endothelial dysfunction in CVD have not been completely elucidated. Here we report that 26S proteasome activation by peroxynitrite (ONOO⁻) is a common pathway for endothelial dysfunction in mouse models of diabetes, hypertension, and dyslipidemia. Endothelial function, assayed by acetylcholine-induced vasorelaxation, was impaired in parallel with significantly increased 26S proteasome activity in aortic homogenates from streptozotocin (STZ)-induced type I diabetic mice, angiotensin-infused hypertensive mice, and high fat-diets -fed LDL receptor knockout (LDLr^−/−) mice. The elevated 26S proteasome activities were accompanied by ONOO⁻-mediated PA700/S10B nitration and increased 26S proteasome assembly and caused accelerated degradation of molecules (such as GTPCH I and thioredoxin) essential to endothelial homeostasis. Pharmacological (administration of MG132) or genetic inhibition (siRNA knockdown of PA700/S10B) of the 26S proteasome blocked the degradation of the vascular protective molecules and ablated endothelial dysfunction induced by diabetes, hypertension, and western diet feeding. Taken together, these results suggest that 26S proteasome activation by ONOO⁻-induced PA700/S10B tyrosine nitration is a common route for endothelial dysfunction seen in mouse models of hypertension, diabetes, and dyslipidemia.

EFNS guidelines on diagnosis and treatment of primary dystonias

OBJECTIVES

to provide a revised version of earlier guidelines published in 2006.

BACKGROUND

primary dystonias are chronic and often disabling conditions with a widespread spectrum mainly in young people.

DIAGNOSIS

primary dystonias are classified as pure dystonia, dystonia plus or paroxysmal dystonia syndromes. Assessment should be performed using a validated rating scale for dystonia. Genetic testing may be performed after establishing the clinical diagnosis. DYT1 testing is recommended for patients with primary dystonia with limb onset before age 30, and in those with an affected relative with early-onset dystonia. DYT6 testing is recommended in early-onset or familial cases with cranio-cervical dystonia or after exclusion of DYT1. Individuals with early-onset myoclonus should be tested for mutations in the DYT11 gene. If direct sequencing of the DYT11 gene is negative, additional gene dosage is required to improve the proportion of mutations detected. A levodopa trial is warranted in every patient with early-onset primary dystonia without an alternative diagnosis. In patients with idiopathic dystonia, neurophysiological tests can help with describing the pathophysiological mechanisms underlying the disorder.

TREATMENT

botulinum toxin (BoNT) type A is the first-line treatment for primary cranial (excluding oromandibular) or cervical dystonia; it is also effective on writing dystonia. BoNT/B is not inferior to BoNT/A in cervical dystonia. Pallidal deep brain stimulation (DBS) is considered a good option, particularly for primary generalized or cervical dystonia, after medication or BoNT have failed. DBS is less effective in secondary dystonia. This treatment requires a specialized expertise and a multidisciplinary team.

Dopa-responsive dystonia

Clinical characteristics and pahophysiologies of dopa-responsive dystonia are discussed by reviewing autosomal-dominant GTP cyclohydrolase-I deficiency (AD GCHI D), recessive deficiencies of enzymes of pteridine metabolism, and recessive tyrosine hydroxylase (TH). Pteridine and TH metabolism involve TH activities in the terminals of the nigrostriatal dopamine neuron which show high in early childhood and decrease exponentially with age, attaining stational low levels by the early 20s. In these disorders, TH in the terminals follows this course with low levels and develops particular symptoms with functional maturation of the downstream structures of the basal ganglia; postural dystonia through the direct pathway and descending output matured earlier in early childhood and parkinsonism in TH deficiency in teens through the D2 indirect pathway ascending output matured later. In action-type AD GCHI D, deficiency of TH in the terminal on the subthalamic nucleus develops action dystonia through the descending output in childhood, focal and segmental dystonia and parkinsonism in adolescence and adulthood through the ascending pathway maturing later. Dysfunction of dopamine in the terminals does not cause degenerative changes or higher cortical dysfunction. In recessive disorders, hypofunction of serotonin and noradrenaline induces hypofunction of the dopamine in the perikaryon and shows cortical dysfunction.

Early-onset L-dopa-responsive parkinsonism with pyramidal signs due to ATP13A2, PLA2G6, FBXO7 and spatacsin mutations

Seven autosomal recessive genes associated with juvenile and young-onset Levodopa-responsive parkinsonism have been identified. Mutations in PRKN, DJ-1, and PINK1 are associated with a rather pure parkinsonian phenotype, and have a more benign course with sustained treatment response and absence of dementia. On the other hand, Kufor-Rakeb syndrome has additional signs, which distinguish it clearly from Parkinson's disease including supranuclear vertical gaze palsy, myoclonic jerks, pyramidal signs, and cognitive impairment. Neurodegeneration with brain iron accumulation type I (Hallervorden-Spatz syndrome) due to mutations in PANK2 gene may share similar features with Kufor-Rakeb syndrome. Mutations in three other genes, PLA2G6 (PARK14), FBXO7 (PARK15), and Spatacsin (SPG11) also produce clinical similar phenotypes in that they presented with rapidly progressive parkinsonism, initially responsive to Levodopa treatment but later, developed additional features including cognitive decline and loss of Levodopa responsiveness. Here, using homozygosity mapping and sequence analysis in families with complex parkinsonisms, we identified genetic defects in the ATP13A2 (1 family), PLA2G6 (1 family) FBXO7 (2 families), and SPG11 (1 family). The genetic heterogeneity was surprising given their initially common clinical features. On careful review, we found the FBXO7 cases to have a phenotype more similar to PRKN gene associated parkinsonism. The ATP13A2 and PLA2G6 cases were more seriously disabled with additional swallowing problems, dystonic features, severe in some, and usually pyramidal involvement including pyramidal weakness. These data suggest that these four genes account for many cases of Levodopa responsive parkinsonism with pyramidal signs cases formerly categorized clinically as pallido-pyramidal syndrome.