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Lysosomal storage disorders (LSDs) constitute a large group of rare, multisystemic, progressive, inherited disorders of metabolism. The aberrant metabolic processes often lead to the cellular accumulation of incompletely metabolized macromolecules or their metabolic byproducts. Most of the patients affected by LSD can experience a variety of neurological presentations including, but not limited to, psychiatric complications, seizures, and/or developmental delays. The onset of symptoms can range from birth to adulthood, and disease severity can vary. Since there is significant overlap in the symptomatology of LSDs, diagnosis is typically confirmed through biochemical and molecular assays. There are currently no approved cures for any LSDs; however, in most cases, treatment of symptoms can lead to better outcomes and improvements in quality of life. The use of hematopoietic stem cell transplantation, enzyme replacement or substrate reduction therapy, and viral vector gene transfer is the subject of many ongoing and completed clinical trials. In this mini review, we provide an overview of LSDs with neurological manifestations, describe the current endeavors in alleviating peripheral symptoms and discuss effective therapeutics strategies.

Here we evaluated the utility of MRI to monitor intrathecal infusions in nonhuman primates. Adeno-associated virus (AAV) spiked with gadoteridol, a gadolinium-based MRI contrast agent, enabled real-time visualization of infusions delivered either via cerebromedullary cistern, lumbar, cerebromedullary and lumbar, or intracerebroventricular infusion. The kinetics of vector clearance from the cerebrospinal fluid (CSF) were analyzed. Our results highlight the value of MRI in optimizing the delivery of infusate into CSF. In particular, MRI revealed differential patterns of infusate distribution depending on the route of delivery. Gadoteridol coverage analysis showed that cerebellomedullary cistern delivery was a reliable and effective route of injection, achieving broad infusate distribution in the brain and spinal cord, and was even greater when combined with lumbar injection. In contrast, intracerebroventricular injection resulted in strong cortical coverage but little spinal distribution. Lumbar injection alone led to the distribution of MRI contrast agent mainly in the spinal cord with little cortical coverage, but this delivery route was unreliable. Similarly, vector clearance analysis showed differences between different routes of delivery. Overall, our data support the value of monitoring CSF injections to dissect different patterns of gadoteridol distribution based on the route of intrathecal administration. Keywords: gene therapy, AAV vector, non-human primates, intrathecal infusion, cisterna magna, lumbar, intracerebroventricular, pharmacokinetics, magnetic resonance imaging, cerebrospinal fluid

The present study was designed to characterize transduction of non-human primate brain and spinal cord with a modified adeno-associated virus serotype 2, incapable of binding to theheparan sulfate proteoglycan receptor, referred to as AAV2-HBKO. AAV2-HBKO was infused into the thalamus, intracerebroventricularly or via a combination of both intracerebroventricular and thalamic delivery. Thalamic injection of this modified vector encoding GFP resulted in widespread CNS transduction that included neurons in deep cortical layers, deep cerebellar nuclei, several subcortical regions, and motor neuron transduction in the spinal cord indicative of robust bidirectional axonal transport. Intracerebroventricular delivery similarly resulted in widespread cortical transduction, with one striking distinction that oligodendrocytes within superficial layers of the cortex were the primary cell type transduced. Robust motor neuron transduction was also observed in all levels of the spinal cord. The combination of thalamic and intracerebroventricular delivery resulted in transduction of oligodendrocytes in superficial cortical layers and neurons in deeper cortical layers. Several subcortical regions were also transduced. Our data demonstrate that AAV2-HBKO is a powerful vector for the potential treatment of a wide number of neurological disorders, and highlight that delivery route can significantly impact cellular tropism and pattern of CNS transduction.

Background In non-human primate (NHP) optogenetics, infecting large cortical areas with viral vectors is often a difficult and time-consuming task. Previous work has shown that parenchymal delivery of adeno-associated virus (AAV) in the thalamus by convection-enhanced delivery (CED) can lead to large-scale transduction via axonal transport in distal areas including cortex. We used this approach to obtain widespread cortical expression of light-sensitive ion channels. New method AAV vectors co-expressing channelrhodopsin-2 (ChR2) and yellow fluorescent protein (YFP) genes were infused into thalamus of three rhesus macaques under MR-guided CED. After six to twelve weeks recovery, in vivo optical stimulation and single cell recording in the cortex was carried out using an optrode in anesthetized animals. Post-mortem immunostaining against YFP was used to estimate the distribution and level of expression of ChR2 in thalamus and cortex. Results Histological analysis revealed high levels of transduction in cortical layers. The patterns of expression were consistent with known thalamo-cortico-thalamic circuits. Dense expression was seen in thalamocortiocal axonal fibers in layers III , IV and VI and in pyramidal neurons in layers V and VI, presumably corticothalamic neurons. In addition we obtained reliable in vivo light-evoked responses in cortical areas with high levels of expression. Comparison with existing methods Thalamic CED is very efficient in achieving large expressing areas in comparison to convectional techniques both in minimizing infusion time and in minimizing damage to the brain. Conclusion MR-guided CED infusion into thalamus provides a simplified approach to transduce large cortical areas by thalamo-cortico-thalamic projections in primate brain.

Niemann-Pick disease type A (NPD-A) is a lysosomal storage disorder characterized by neurodegeneration and early death. It is caused by loss-of-function mutations in the gene encoding for acid sphingomyelinase (ASM), which hydrolyzes sphingomyelin into ceramide. Here, we evaluated the safety of cerebellomedullary (CM) cistern injection of adeno-associated viral vector serotype 9 encoding human ASM (AAV9-hASM) in nonhuman primates (NHP). We also evaluated its therapeutic benefit in a mouse model of the disease (ASM-KO mice). We found that CM injection in NHP resulted in widespread transgene expression within brain and spinal cord cells without signs of toxicity. CM injection in the ASM-KO mouse model resulted in hASM expression in cerebrospinal fluid and in different brain areas without triggering an inflammatory response. In contrast, direct cerebellar injection of AAV9-hASM triggered immune response. We also identified a minimally effective therapeutic dose for CM injection of AAV9-hASM in mice. Two months after administration, the treatment prevented motor and memory impairment, sphingomyelin (SM) accumulation, lysosomal enlargement, and neuronal death in ASM-KO mice. ASM activity was also detected in plasma from AAV9-hASM CM-injected ASM-KO mice, along with reduced SM amount and decreased inflammation in the liver. Our results support CM injection for future AAV9-based clinical trials in NPD-A as well as other lysosomal storage brain disorders. © 2019 The Authors., This work was supported by Wylder Nation Foundation and by grants from Spanish Ministry of Economy and Competitivity (SAF-2014-57539-R and SAF2017-87698-R) to M.D.L. and from NIH-NINDS (R01NS073940) to K.S.B. A.P-C was a recipient of the FPU pre-doctoral fellowship from the Spanish Ministry of Economy and Competitivity. L.S. was a recipient of the Edward H. Schuchman Research Fellowship from the National Niemann-Pick Disease Foundation. E.H.S. and X.H. were supported by a MERIT award from the NIH (R37 HD28607) to E.H.S.

OBJECTIVETo develop and assess a convective delivery technique that enhances the effectiveness of drug delivery to nonspherical brain nuclei, the authors developed an occipital “infuse-as-you-go” approach to the putamen and compared it to the currently used transfrontal approach.METHODSEleven nonhuman primates received a bilateral putamen injection of adeno-associated virus with 2 mM gadolinium-DTPA by real-time MR-guided convective perfusion via either a transfrontal (n = 5) or occipital infuse-as-you-go (n = 6) approach.RESULTSMRI provided contemporaneous assessment and monitoring of putaminal infusions for transfrontal (2 to 3 infusion deposits) and occipital infuse-as-you-go (stepwise infusions) putaminal approaches. The infuse-as-you-go technique was more efficient than the transfrontal approach (mean 35 ± 1.1 vs 88 ± 8.3 minutes [SEM; p < 0.001]). More effective perfusion of the postcommissural and total putamen was achieved with the infuse-as-you-go versus transfronatal approaches (100-µl infusion volumes; mean posterior commissural coverage 76.2% ± 5.0% vs 32.8% ± 2.9% [p < 0.001]; and mean total coverage 53.5% ± 3.0% vs 38.9% ± 2.3% [p < 0.01]).CONCLUSIONSThe infuse-as-you-go approach, paralleling the longitudinal axis of the target structure, provides a more effective and efficient method for convective infusate coverage of elongated, irregularly shaped subcortical brain nuclei.

Gene therapy shows great promise for the treatment of neurological disorders, and accessing cerebrospinal fluid (CSF) from the cerebellomedullary cistern through the posterior atlanto-occipital membrane has become a common route of delivery in preclinical studies. Unlike direct brain parenchymal infusions, CSF delivery offers broader coverage to the central and peripheral nervous system. This prospectively increases its translational value, more specially to treat global brain dysfunctions in which the pathology is disseminated throughout the brain and not focalized in one specific brain structure. Also, from the practical point of view, this approach offers a more reliable method for neurological gene replacement in infants, whose immature cranial suture preclude the use of skull-mounted devices. Here we describe a consistent, precise, and safe method for CSF injection.

Focus on the purinergic receptor P2Y11 has increased following the finding of an association between the sleep disorder narcolepsy and a genetic variant in P2RY11 causing decreased gene expression. Narcolepsy is believed to arise from an autoimmune destruction of the hypothalamic neurons that produce the neuropeptide hypocretin/orexin. It is unknown how a decrease in expression of P2Y11 might contribute to an autoimmune reaction towards the hypocretin neurons and the development of narcolepsy. To advance narcolepsy research it is therefore extremely important to determine the neuroanatomical localization of P2Y11 in the brain with particular emphasis on the hypocretin neurons. In this article we used western blot, staining of blood smears, and flow cytometry to select two antibodies for immunohistochemical staining of macaque monkey brain. Staining was seen in neuron-like structures in cortical and hypothalamic regions. Rats do not have a gene orthologue to the P2Y11 receptor and therefore rat brain was used as negative control tissue. The chromogenic signal observed in macaque monkey brain in neurons was not considered reliable, because the antibodies stained rat brain in a similar distribution pattern. Hence, the neuroanatomical localization of the P2Y11 receptor remains undetermined due to the lack of specific P2Y11 antibodies for brain immunohistochemistry.

Gene therapy shows great promise for the treatment of neurological disorders, and accessing cerebrospinal fluid (CSF) from the cerebellomedullary cistern through the posterior atlanto-occipital membrane has become a common route of delivery in preclinical studies. Unlike direct brain parenchymal infusions, CSF delivery offers broader coverage to the central and peripheral nervous system. This prospectively increases its translational value, more specially to treat global brain dysfunctions in which the pathology is disseminated throughout the brain and not focalized in one specific brain structure. Also, from the practical point of view, this approach offers a more reliable method for neurological gene replacement in infants, whose immature cranial suture preclude the use of skull-mounted devices. Here we describe a consistent, precise, and safe method for CSF injection.

OBJECTIVESuccessful convection-enhanced delivery of therapeutic agents to subcortical brain structures requires accurate cannula placement. Stereotactic guiding devices have been developed to accurately target brain nuclei. However, technologies remain limited by a lack of MRI compatibility, or by devices’ size, making them suboptimal for direct gene delivery to brain parenchyma. The goal of this study was to validate the accuracy of a novel frameless skull-mounted ball-joint guide array (BJGA) in targeting the nonhuman primate (NHP) brain.METHODSFifteen MRI-guided cannula insertions were performed on 9 NHPs, each targeting the putamen. Optimal trajectories were planned on a standard MRI console using 3D multiplanar baseline images. After cannula insertion, the intended trajectory was compared to the final trajectory to assess deviation (euclidean error) of the cannula tip.RESULTSThe average cannula tip deviation was 1.18 ± 0.60 mm (mean ± SD) as measured by 2 independent reviewers. Topological analysis showed a superior, posterior, and rightward directional bias, and the intra- and interclass correlation coefficients were > 0.85, indicating valid and reliable intra- and interobserver evaluation.CONCLUSIONSThe data demonstrate that the BJGA can be used to reliably target subcortical brain structures by using MRI guidance, with accuracy comparable to current frameless stereotactic systems. The size and versatility of the BJGA, combined with a streamlined workflow, allows for its potential applicability to a variety of intracranial neurosurgical procedures, and for greater flexibility in executing MRI-guided experiments within the NHP brain.

Brain-derived neurotrophic factor (BDNF) gene delivery to the entorhinal cortex is a candidate for treatment of Alzheimer's disease (AD) to reduce neurodegeneration that is associated with memory loss. Accurate targeting of the entorhinal cortex in AD is complex due to the deep and atrophic state of this brain region. Using MRI-guided methods with convection-enhanced delivery, we were able to accurately and consistently target AAV2-BDNF delivery to the entorhinal cortex of non-human primates; 86 ± 3% of transduced cells in the targeted regions co-localized with the neuronal marker NeuN. The volume of AAV2-BDNF (3 × 108 vg/µl) infusion linearly correlated with the number of BDNF labeled cells and the volume (mm3) of BDNF immunoreactivity in the entorhinal cortex. BDNF is normally trafficked to the hippocampus from the entorhinal cortex; in these experiments, we also found that BDNF immunoreactivity was elevated in the hippocampus following therapeutic BDNF vector delivery to the entorhinal cortex, achieving growth factor distribution through key memory circuits. These findings indicate that MRI-guided infusion of AAV2-BDNF to the entorhinal cortex of the non-human primate results in safe and accurate targeting and distribution of BDNF to both the entorhinal cortex and the hippocampus. These methods are adaptable to human clinical trials.

In Parkinson’s disease (PD), aromatic L-amino acid decarboxylase (AADC) is the rate-limiting enzyme in the conversion of L-DOPA (Sinemet) to dopamine (DA). Previous studies in PD animal models demonstrated that lesion of dopaminergic neurons is associated with profound loss of AADC activity in the striatum, blocking efficient conversion of L-DOPA to DA. Relatively few studies have directly analyzed AADC in PD brains. Thus, the aim of this study was to gain a better understanding of regional changes in AADC activity, DA, serotonin and their monoamine metabolites in the striatum of PD patients and experimentally lesioned animals (rat and MPTP-treated nonhuman primate, NHP). Striatal AADC activity was determined post mortem in neuropathologically confirmed PD subjects, animal models and controls. A regional analysis was performed for striatal AADC activity and monoamine levels in NHP tissue. Interestingly, analysis of putaminal AADC activity revealed that control human striatum contained much less AADC activity than rat and NHP striata. Moreover, a dramatic loss of AADC activity in PD striatum compared to controls was detected. In MPTP-treated NHP, caudate nucleus was almost as greatly affected as putamen, although mean DA turnover was higher in caudate nucleus. Similarly, DA and DA metabolites were dramatically reduced in different regions of PD brains, including caudate nucleus, whereas serotonin was relatively spared. After L-DOPA administration in MPTP-treated NHP, very poor conversion to DA was detected, suggesting that AADC in NHP nigrostriatal fibers is mainly responsible for L-DOPA to DA conversion. These data support further the rationale behind viral gene therapy with AAV2-hAADC to restore AADC levels in putamen and suggest further the advisability of expanding vector delivery to include coverage of anterior putamen and the caudate nucleus.

Protein aggregation as a result of misfolding is a common theme underlying neurodegenerative diseases. Accordingly, most recent studies aim to prevent protein misfolding and/or aggregation as a strategy to treat these pathologies. For instance, state-of-the-art approaches, such as silencing protein overexpression by means of RNA interference, are being tested with positive outcomes in preclinical models of animals overexpressing the corresponding protein. Therapies designed to treat central nervous system diseases should provide accurate delivery of the therapeutic agent and long-term or chronic expression by means of a nontoxic delivery vehicle. After several years of technical advances and optimization, gene therapy emerges as a promising approach able to fulfill those requirements. In this review we will summarize the latest improvements achieved in gene therapy for central nervous system diseases associated with protein misfolding (e.g., amyotrophic lateral sclerosis, Alzheimer’s, Parkinson’s, Huntington’s, and prion diseases), as well as the most recent approaches in this field to treat these pathologies.

The present study builds on previous work showing that infusion of adeno-associated virus type 9 (AAV9) into the cisterna magna (CM) of nonhuman primates resulted in widespread transduction throughout cortex and spinal cord. Transduction efficiency was severely limited, however, by the presence of circulating anti-AAV antibodies. Accordingly, we compared AAV9 to a related serotype, AAV7, which has a high capsid homology. CM infusion of either AAV7 or AAV9 directed high level of cell transduction with similar patterns of distribution throughout brain cortex and along the spinal cord. Dorsal root ganglia and corticospinal tracts were also transduced. Both astrocytes and neurons were transduced. Interestingly, little transduction was observed in peripheral organs. Our results indicate that intrathecal delivery of either AAV7 or AAV9 directs a robust and widespread cellular transduction in the central nervous system and other peripheral neural structures.

Focus on the purinergic receptor P2Y

Accessing cerebrospinal fluid (CSF) from the craniocervical junction through the posterior atlanto-occipital membrane via cerebellomedullary injection (also known as cisternal puncture or cisterna magna injection) has become a standard procedure in preclinical studies. Such delivery provides broader coverage to the central and peripheral nervous system unlike local parenchymal delivery alone. As a clinical application, this approach offers a more reliable method for neurological gene replacement delivery in infants, where skull-mounted devices are not indicated. Here we describe a consistent, precise, and safe method for CSF injection with minimal equipment and technical skills.

In this review, we discuss recent developments in the delivery of adeno-associated virus-based vectors (AAV), particularly with respect to the role of axonal transport in vector distribution in the brain. The use of MRI-guidance and new stereotactic aiming devices have now established a strong foundation for neurological gene therapy to become an accepted procedure in interventional neurology.

We have previously shown that adeno-associated virus type 2 (AAV2) undergoes anterograde axonal transport in rat and non-human primate brain. We screened other AAV serotypes for axonal transport and found that AAV6 is transported almost exclusively in a retrograde direction and, in the same way as AAV2, it is also neuron-specific in rat brain. Our findings show that axonal transport of AAV is serotype dependent and this has implications for gene therapy of neurological diseases such as Huntington's disease.

Microtubule-associated protein tau (MAPT) and apolipoprotein E (APOE) are involved in the pathogenic mechanisms of Alzheimer's disease (AD). We prospectively followed three longitudinal independent samples (total n=319) with amnestic mild cognitive impairment (MCI) and analyzed whether MAPT H1/H2 haplotypes and APOE ε4 polymorphisms accelerated the rate of progression from MCI to dementia. At the end of the study, 172 subjects remained cognitively stable, whereas 147 progressed to dementia. APOE ε4 and MAPT H1/H1 were independently associated with an increased rate of progression to dementia in the combined sample. Cox regression models of the combined MCI sample showed that MAPT H1/H1 carriers had an increased rate of progression to dementia compared with non carriers (Hazard Ratio =1.45; 95% CI=1.04-2.02; p=0.028) and time-to-progression was shortened by 1.37 years. APOE ε4 allele also accelerated progression to dementia (Hazard Ratio=1.47; 95% CI= 1.06-2.04; p=0.020) and reduced the time-to-progression by 0.87 years. Additionally, MAPT H1/H1 genotype and APOE ε4 allele had an additive effect in progression to dementia, increasing progression rate to dementia (Hazard Ratio=2.24, 95% CI =1.40-3.58; p=0.001) and shortening time-to-progression to dementia by 2.92 years. Similar results were obtained when only considering progression to AD-type dementia. Our results suggest that both MAPT H1/H1 genotype and APOE ε4 allele lead to a more rapid progression to dementia among MCI subjects, probably mediating an increased rate of amyloid-β and tau brain deposition.

Background: Parkinson's disease (PD) and essential tremor (ET) may share some etiopathogenic factors. A genome-wide association study has shown that LINGO1 gene variants are associated with increased risk of ET. We hypothesized that LINGO1 variants could increase susceptibility to PD. Methods: A large series of PD subjects and healthy controls were genotyped for rs9652490 and rs11856808 LINGO1 single nucleotide polymorphisms (SNPs). Results: We found an increased frequency of the rs11856808T/T genotype in PD compared with controls (odds ratio = 1.46; corrected P value = 0.02). A recessive genetic model was the best fit for rs11856808 influence on PD (recessive gene action test: corrected P value = 0.01). Stratification analysis showed that rs11856808T/T genotype frequency was higher in the tremor-dominant PD and the classical PD (C-PD) subgroups (recessive gene action test for the C-PD subgroup: corrected P value = 0.004). Discussion: Our results indicate that LINGO1 variants could increase risk of PD, specifically those presenting the non-rigid-akinetic phenotypes, which suggests that LINGO1 may have a role in the etiology of tremor in PD at least in the Spanish population. © 2010 Movement Disorder Society

Eighteen loci and several susceptibility genes have been related to Parkinson's disease (PD). However, most studies focus on single genes in small PD series. Our aim was to establish the genetic background of a large Spanish PD sample. Pooled-DNA target sequencing of 7 major PD genes (SNCA, PARK2, PINK1, DJ-1, LRRK2, GBA, and MAPT) was performed in 562 PD cases. Forty-four variants were found among 114 individuals (20.28%, p0.05). Among these variants, 30 were found in Mendelian genes (68.18%) and 14 in PD susceptibility genes (31.82%). Seven novel variants were identified. Interestingly, most variants were found in PARK2 and PINK1 genes, whereas SNCA and DJ-1 variants were rare. Validated variants were also genotyped in Spanish healthy controls (n = 597). Carriers of heterozygous PARK2 variants presented earlier disease onset and showed dementia more frequently. PD subjects carrying 2 variants at different genes (1.42%) had an earlier age of onset and a predominantly akinetic-rigid PD phenotype (55.6%, p0.05), suggesting that the accumulation of genetic risk variants could modify PD phenotype.

Phosphatase and tensin homolog-induced putative kinase 1 gene mutations have been associated with autosomal recessive early-onset Parkinson's disease. To date, no neuropathological reports have been published from patients with Parkinson's disease with both phosphatase and tensin homolog-induced putative kinase 1 gene copies mutated. We analysed the coding region of phosphatase and tensin homolog-induced putative kinase 1 gene in a large Spanish family with six members with parkinsonism. The phenotype was characterized by an early-onset (mean: 31.6, standard deviation: 9.6 years, range: 14-45 years), slowly progressive levodopa-responsive parkinsonism, initial gait impairment and psychiatric symptoms. We identified two segregating pathogenic phosphatase and tensin homolog-induced putative kinase 1 mutations that were either in homozygous or heterozygous compound state in all affected family members. We found an exon 7 deletion (g.16089_16383del293; c.1252_1488del) and a novel+1U1-dependent 5' splice-site mutation in exon 7 (g.16378G>A; c.1488+1G>A). Leukocyte-derived messenger RNA analysis showed that both mutations caused exon 7 skipping and c.1488+1G>A also lead to an in-frame transcript with a 33 base-pair deletion (p.L485_R497del) resulting from activation of a 5' cryptic exon 7 splice site. Single photon emission computed tomography quantification of striatal dopamine transporter binding (123I-Ioflupane) revealed a posterior-anterior gradient similar to that of idiopathic Parkinson's disease, but there was no correlation between striatal reduced uptake and disease duration. Post-mortem neuropathological examination of an early-onset Parkinson's disease carrier of two heterozygous compound phosphatase and tensin homolog-induced putative kinase 1 mutations showed neuronal loss in the substantia nigra pars compacta, Lewy bodies and aberrant neurites in the reticular nuclei of the brainstem, substantia nigra pars compacta and Meynert nucleus, but the locus ceruleus and the amygdala were spared. This is the first neuropathological report of the brain from an early-onset phosphatase and tensin homolog-induced putative kinase 1-linked parkinsonism showing that mutated phosphatase and tensin homolog-induced putative kinase 1 protein induces Lewy body pathology. Unbalanced preservation of the locus ceruleus may well play a role in the slow evolution of motor symptoms and, probably, in the psychiatric symptoms often encountered in Parkinson's disease associated with phosphatase and tensin homolog-induced putative kinase 1 mutation.

Background and purpose: Linkage analysis in familial Parkinson’s disease (PD) identified a locus in 2q36-37 (PARK11). Sequencing of GIGYF2 identified several variants only present amongst PD individuals. Methods: We analyzed the presence of disease-associated GIGYF2 variants in familial and sporadic PD from Spanish origin by sequencing of 147 PD individuals. The entire GIGYF2 coding sequence was analyzed in 122 familial PD individuals and exons 2, 4, 8–11, 14 and 25–26 were sequenced in 25 sporadic PD to identify disease-associated variants. Results: We found no variants associated with PD and failed to identify any of previously PD-associated GIGYF2 variants in our sample. We identified four novel missense changes in GIGYF2. p.Met48Ile was found in a PD individual who also was a carrier of two PARKIN mutations. p.Q1244_Q1247del variant was present only in one PD individual but not found in 70 controls. However, its location in the highly polymorphic GIGYF2 glutamine/proline-rich region does not support a role in PD. Two variants (p.P1238insAGC and p.Q1249del) were present both in PD subjects and in controls. Additionally, the p.L1230_Q1237del variant, which was previously considered as a PD-associated change, was found in one control. Conclusion: Our findings suggest that GIGYF2 mutations are not a frequent cause of PD in the Spanish population, since we found no clearly segregating variants. We propose further analyses in PD subjects from different populations to define the role of GIGYF2. A clear pathogenic mutation in other gene at 2q36-37 in the PARK11-linked PD families would definitively disprove GIGYF2 as the responsible gene.

The role of the plasma level of homocysteine (Hcy), as a primary outcome, and the effect of silent cerebrovascular lesions and genetic variants related to Hcy metabolism, as secondary outcomes, in the cognitive decline and dementia in Parkinson's disease (PD) were studied. This case–control study focused on 89 PD patients of minimum 10 years of evolution and older than 60 years, who were neuropsychologically classified either as cognitively normal (n = 37), having mild cognitive impairment (Petersen criteria) (n = 22), or suffering from dementia (DSM-IV) (n = 30), compared with cognitively normal age-matched control subjects (n = 30). Plasma levels of Hcy, vitamins B12 and B6, folic acid, polymorphisms in genes related to Hcy metabolism (MTHFR, MTR, MTRR, and CBS) and silent cerebrovascular events were analyzed. Plasma levels of Hcy were increased in PD patients (P = 0.0001). There were no differences between the groups of patients. The brain vascular burden was similar among PD groups. There was no association between polymorphisms in the studied genes and the Hcy plasma levels or cognitive status in PD patients. We found no evidence for a direct relationship between Hcy plasma levels and cognitive impairment and dementia in PD. No indirect effect through cerebrovascular disease or genetic background was found either. © 2009 Movement Disorder Society

Background: Autosomal recessive hereditary spastic paraparesis with thin corpus callosum (ARHSP-TCC) is being increasingly recognized as a variety of spastic paraplegia with mental retardation. SPG11 gene mutations have been reported to be associated with ARHSP-TCC. Methods: As an independent group, we investigated SPG11 gene involvement in four individuals not previously described with either recessive or sporadic HSP-TCC presentation. Results: Chromosome 15q13-15 segregating autosomal disease haplotypes were different across the kindreds and sequencing of SPG11 identified four novel frameshift/nonsense segregating mutations and the R2034X mutation, which were in heterozygous compound status. The affected examined had decreased thalamic and bilateral paracentral frontal lobe metabolism on 18 F-flurodeoxyglucose PET. Conclusions: Loss-of-function SPG11 mutations are the major cause of autosomal recessive hereditary spastic paraparesis with thin corpus callosum in Southern Europe, even in apparently sporadic cases. Decreased thalamic metabolism was consistently a phenotypical SPG11 mutation hallmark.

The use of viral vectors to express therapeutics genes in Parkinson’s disease (PD) trials has been hindered by a lack of understanding of the principles that guide effective distribution of vectors within the basal ganglia, even when we have a strong expectation of efficacy based on experimentation in animal models. The major problems we have faced include (1) scale-up from small rodent and nonhuman primates (NHP) brains to humans, (2) understanding how viral vectors distribute within the brain parenchyma, (3) prediction of how viral particles are disseminated by neuronal projections after direct delivery to the putamen and substantia nigra, (4) the mechanism of action of the therapeutic gene on dopaminergic system, and (5) the relevance of animal models to idiopathic PD. In this chapter, we will address these important issues and will try to put them into the context of data that has been obtained from current and recent clinical trials. In particular, we will address therapeutic strategies aimed at restoring dopaminergic function by either expressing genes that encode enzymes responsible for synthesis of dopamine (DA) or expressing growth factors capable of upregulating DA function in the degenerated neurons. We will not address inhibition of outflow innervation from the striatum in PD patients by expressing glutamic acid decarboxylase (GAD) as this strategy is described in the dedicated chapter in this book.

Huntington’s disease (HD) is caused by a toxic gain-of-function associated with the expression of the mutant huntingtin (htt) protein. Therefore, the use of RNA interference to inhibit Htt expression could represent a disease-modifying therapy. The potential of two recombinant adeno-associated viral vectors (AAV), AAV1 and AAV2, to transduce the cortico-striatal tissues that are predominantly affected in HD was explored. Green fluorescent protein was used as a reporter in each vector to show that both serotypes were broadly distributed in medium spiny neurons in the striatum and cortico-striatal neurons after infusion into the putamen and caudate nucleus of nonhuman primates (NHP), with AAV1-directed expression being slightly more robust than AAV2-driven expression. This study suggests that both serotypes are capable of targeting neurons that degenerate in HD, and it sets the stage for the advanced preclinical evaluation of an RNAi-based therapy for this disease.

A pilot study in nonhuman primates was conducted, in which two Rhesus macaques received bilateral parenchymal infusions of adeno-associated virus serotype 9 encoding green fluorescent protein (AAV9-GFP) into each putamen. The post-surgical in-life was restricted to 3 weeks in order to minimize immunotoxicity expected to arise from expression of GFP in antigen-presenting cells. Three main findings emerged from this work. First, the volume over which AAV9 expression was distributed (Ve) was substantially greater than the volume of distribution of MRI signal (Vd). This stands in contrast with Ve/Vd ratio of rAAV2, which is lower under similar conditions. Second, post-mortem analysis revealed expression of GFP in thalamic and cortical neurons as well as dopaminergic neurons projecting from substantia nigra pars compacta, indicating retrograde transport of AAV9. However, fibers in the substantia nigra pars reticulata, a region that receives projections from putamen, also stained for GFP, indicating anterograde transport of AAV9 as well. Finally, one hemisphere received a 10-fold lower dose of vector compared with the contralateral hemisphere (1.5 × 10(13) vg ml(-1)) and we observed a much stronger dose effect on anterograde-linked than on retrograde-linked structures. These data suggest that AAV9 can be axonally transported bi-directionally in the primate brain. This has obvious implications to the clinical developing of therapies for neurological disorders like Huntington's or Alzheimer's diseases.

Gene transfer technology offers great promise as a potential therapeutic approach to the brain but has to be viewed as a very complex technology. Success of ongoing clinical gene therapy trials depends on many factors such as selection of the correct genetic and anatomical target in the brain. In addition, selection of the viral vector capable of transfer of therapeutic gene into target cells, along with long-term expression that avoids immunotoxicity has to be established. As with any drug development strategy, delivery of gene therapy has to be consistent and predictable in each study subject. Failed drug and vector delivery will lead to failed clinical trials. In this article, we describe our experience with AAV viral vector delivery system, that allows us to optimize and monitor in real time viral vector administration into affected regions of the brain. In addition to discussing MRI-guided technology for administration of AAV vectors we have developed and now employ in current clinical trials, we also describe ways in which infusion cannula design and stereotactic trajectory may be used to maximize the anatomical coverage by using fluid backflow. This innovative approach enables more precise coverage by fitting the shape of the infusion to the shape of the anatomical target.

Adeno-associated virus serotype 2 (AAV2) has previously been reported to be a slowly uncoating virus in peripheral tissues, but persistence of intact vector in primate brain has not been explored. Because some neurological gene therapies may require re-administration of the same vector to patients, it seems important to understand the optimal timeframe in which to consider such repeat intervention. Surprisingly, convection-enhanced delivery of AAV2 into the thalamus of nonhuman primates (NHPs) resulted in robust staining of neurons with A20 antibody that detected intact AAV2 particles at ∼1.5 months after infusion. However, by 2.5 months, no A20 staining was visible. These data confirmed earlier findings of persistence of intact AAV2 particles in ocular and hepatic tissues. In order to probe the potential consequences of this persistence, we infused AAV2-human aromatic L-amino acid decarboxylase into left and right thalamus of three NHPs, with a 3-month delay between infusions. During that interval, we immunized each animal subcutaneously with AAV2 virus-like particles (empty vector) in order to induce strong anti-capsid humoral immunity. Various high neutralizing antibody titers were achieved. The lowest titer animal showed infiltration of B lymphocytes and CD8(+) T cells into both the secondary and primary infusion sites. In the other two animals, extremely high titers resulted in no transduction of the second site and, therefore, no lymphocytic infiltration. However, such infiltration was prominent at the primary infusion site in each animal and was associated with overt neuronal loss and inflammation.

Widespread distribution of gene products at clinically relevant levels throughout the central nervous system (CNS) without involving peripheral organs is still a challenge. Previous work demonstrated that infusion of adeno-associated virus (AAV) serotypes 9 (AAV9) and 7 (AAV7) into the cerebrospinal fluid (CSF) via cisterna magna of nonhuman primates (NHP) resulted in widespread transduction throughout cortex and spinal cord. Adeno-associated virus serotype 5 (AAV5) is also a potential candidate for CNS gene therapy when delivered into brain parenchyma but its performance in CSF has not been described. In the present work, we compared transduction patterns after CSF and parenchymal delivery of AAV5-GFP. For CSF delivery, we injected various doses of AAV5 (1E+14, 1E+13 and 1E+12 vg/mL) into CSF via lumbar routes in naive NHP and studied vector distribution and cellular transduction 4 weeks after CSF delivery. We found a dose-dependent increase in transduction with strong levels of cell transduction and distribution throughout cortex and along the spinal cord at the highest doses and no signal in the low-dose group. These results suggest a dose threshold when delivering into CSF, most likely due to a dilution of the viral particles. Both astrocytes and neurons were transduced by AAV5 when infused either in CSF or directly into brain parenchyma.Parenchymal delivery of AAV5-GFP was analyzed 8 weeks after surgery. Interestingly, when infused into the thalamus and the contralateral putamen, AAV5 resulted in higher levels of expression in cortical and subcortical structures than those observed in high-dose CSF animals. Surprisingly, thalamic injection directed spinal cord transduction throughout the cortico-bulbar axis. These results suggest not only that smaller volumes of AAV5 infused directly into the thalamus can result in robust and widespread cellular transduction in the brain but also to spinal cord. Our results confirm AAV5 as a powerful viral vector for gene transfer in the CNS and underscore its translational potential for treating neurological disorders of the brain and spinal cord.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) and α-synuclein (SNCA) genes are known genetic causes of Parkinson's disease (PD). Recently, a genetic variant in SNCA has been associated with a lower age at onset in idiopathic PD (IPD). We genotyped the SNCA polymorphism rs356219 in 84 LRRK2-associated PD patients carrying the G2019S mutation. We found that a SNCA genetic variant is associated with an earlier age at onset in LRRK2-associated PD. Our results support the notion that SNCA variants can modify the pathogenic effect of LRRK2 mutations as described previously for IPD.

Many studies have demonstrated that adeno-associated virus serotype 9 (AAV9) transduces astrocytes and neurons when infused into rat or nonhuman primate (NHP) brain. We previously showed in rats that transduction of antigen-presenting cells (APC) by AAV9 encoding a foreign protein triggered a full neurotoxic immune response. Accordingly, we asked whether this phenomenon occurred in NHP. We performed parenchymal or intrathecal infusion of AAV9 encoding green fluorescent protein (GFP), a non-self protein derived from jellyfish, or human aromatic L-amino acid decarboxylase (hAADC), a self-protein, in separate NHP. Animals receiving AAV9-GFP into cisterna magna (CM) became ataxic, indicating cerebellar pathology, whereas AAV9-hAADC animals remained healthy. In transduced regions, AAV9-GFP elicited inflammation associated with early activation of astrocytic and microglial cells, along with upregulation of major histocompatibility complex class II (MHC-II) in glia. In addition, we found Purkinje neurons lacking calbindin after AAV9-GFP but not after AAV9-hAADC delivery. Our results demonstrate that AAV9-mediated expression of a foreign-protein, but not self-recognized protein, triggers complete immune responses in NHP regardless of the route of administration. Our results warrant caution when contemplating use of serotypes that can transduce APC if the transgene is not syngeneic with the host. This finding has the potential to complicate preclinical toxicology studies in which such vectors encoding human cDNA's are tested in animals.

AAV-based gene therapy has considerable potential as a therapeutic tool to treat many monogenic diseases by restoring deficient expression of key genes after a single injection of an AAV hosting a functional copy of the gene. Under some circumstances, these diseases may need more than a single administration of the AAV-based therapeutic agent. One of the main concerns related to repeated AAV delivery is inhibition of cell transduction at the second infusion site by neutralizing antibodies (NAb) generated after the first exposure.In the present study, we evaluated the immune response after repeated AAV2 delivery to the brain in AAV2 seronegative Rhesus macaques. We infused AAV2-hAADC into left and right thalamus, with a 91-day delay between vector infusions. We determined the levels of anti-AAV2 NAb in sera weekly to monitor antibody production until necropsy 130 days after the first infusion. To ensure high levels of NAb before second infusion, we boosted the NAb production with 2 intramuscular AAV2-VLP immunizations.AADC expression in the thalamus was analyzed in post-mortem tissue by immunohistochemistry and inhibition of transduction was observed in the second infused hemisphere. Immune markers such as GFAP, Iba1, MHCII, CD8 and CD20 were also analyzed, as well NeuN and H&E, to investigate the extent of the immunologic activation after a second brain delivery. Surprisingly, these markers evinced a more dramatic immune response at the first injection site than at the second, resulting even in neuronal loss at the infusion site. CD20 staining revealed the abundant presence of B-lymphocytes within the infusion site. A20 antibody immunostaining revealed the presence of the AAV2 capsid in both hemispheres suggesting a possible trigger of the immune response.The present work demonstrates that very high levels of NAb generated after a primary injection can impair the transduction levels in the second injection site. Moreover, it shows that infiltration of B-lymphocytes can induce tissue damage under conditions of AAV2 capsid persistence. Further studies will be performed to determine the chronology of the events and then establish optimal design and timeline for serial multiple-administration of the AAV-based therapeutic agents. The data further suggest that use of serotypes, such as AAV2, that clear from tissues slowly may not be suitable for therapies in which readministration is being considered.

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare, autosomal-recessive neurological disorder caused by mutations in the DDC gene that leads to an inability to synthesize catecholamines and serotonin. As a result, patients suffer compromised development, particularly in motor function. A recent gene replacement clinical trial explored putaminal delivery of recombinant adeno-associated virus serotype 2 vector encoding human AADC (AAV2-hAADC) in AADC-deficient children. Unfortunately, patients presented only modest amelioration of motor symptoms, which authors acknowledged could be due to insufficient transduction of putamen. We hypothesize that, with the development of a highly accurate MRI-guided cannula placement technology, a more effective approach might be to target the affected mid-brain neurons directly. Transduction of AADC-deficient dopaminergic neurons in the substantia nigra and ventral tegmental area with locally infused AAV2-hAADC would be expected to lead to restoration of normal dopamine levels in affected children. The objective of this study was to assess the long-term safety and tolerability of bilateral AAV2-hAADC MRI-guided pressurized infusion into the mid-brain of non-human primates. Animals received either vehicle, low or high AAV2-hAADC vector dose and were euthanized 1, 3 or 9 months after surgery. Our data indicate that effective mid-brain transduction was achieved without untoward effects.

We recently demonstrated that axonal transport of adeno-associated virus (AAV) is serotype-dependent. Thus, AAV serotype 2 (AAV2) is anterogradely transported (e.g., from cell bodies to nerve terminals) in both rat and non-human primate (NHP) brain. In contrast, AAV serotype 6 (AAV6) is retrogradely transported from terminals to neuronal cell bodies in the rat brain. However, the directionality of axonal transport of AAV6 in the NHP brain has not been determined. In this study, two Cynomolgus macaques received an infusion of AAV6 harboring green fluorescent protein (GFP) into the striatum (caudate and putamen) by magnetic resonance (MR)-guided convection-enhanced delivery. One month after infusion, immunohistochemical staining of brain sections revealed a striatal GFP expression that corresponded well with MR signal observed during gene delivery. As shown previously in rats, GFP expression was detected throughout the prefrontal, frontal and parietal cortex, as well as the substantia nigra pars compacta and thalamus, indicating retrograde transport of the vector in NHP. AAV6-GFP preferentially transduced neurons, although a few astrocytes were also transduced. Transduction of non-neuronal cells in the brain was associated with the upregulation of the major histocompatibility complex-II and lymphocytic infiltration as previously observed with AAV1 and AAV9. This contrasts with highly specific neuronal transduction in the rat brain. Retrograde axonal transport of AAV6 from a single striatal infusion permits efficient transduction of cortical neurons in significant tissue volumes that otherwise would be difficult to achieve.

This study was performed to investigate the delivery of AAV vectors into the putamen and thalamus of nonhuman primates. The vectors were delivered to the targeted brain regions by MRI-guided convection enhanced delivery. Special attention was given to the analysis of axonal transport and levels of transduction. Recombinant AAV is an excellent candidate for delivery of therapeutic molecules to the central nervous system to target neurodegenerative diseases. UniQure has succeeded in developing a proprietary platform manufacturing technology that allows safe, effective, cGMP-compliant, economically feasible and commercially scalable manufacturing of AAV. UniQure's novel approach is based on the use of a combination of recombinant baculoviruses and insect cells. Using our production platform, two AAV stocks encoding GDNF or GFP were generated. At eight weeks following infusion into the thalamus, for instance, massive transduction of the thalamus, cortex, striatum and substantia nigra was observed indicating both anterograde and retrograde transduction. At the site of injection, transduction was both glial and neuronal, whereas off site transduction was mainly neuronal. Following injection of a lower AAV volume into the putamen, transduction was limited to areas within the putamen and substantia nigra suggesting only anterograde transport of viral particles. These data indicate a dose dependent anterograde or retrograde transport mechanism. This data set confirms that production of AAV using the (scalable) baculovirus-based platform results in an effective vector that is able to mediate expression patterns that can be used to develop an AAV-mediated therapeutic strategy to treat neurodegenerative diseases.

PRKN mutations have been linked to Parkinson’s disease (PD). Most of the mutational screenings have focused on the coding exons. The 3′ untranslated region (UTR) could also harbor functionally relevant nucleotide changes. We performed a mutational screening of PRKN in a cohort of early-onset PD patients (n = 235) from Spain. We found 16 mutations (five new): 16 patients (7 %) carried two mutations and only one mutation was found in 28 (12 %). Patients with two mutations had significantly lower mean age (30 ± 9 years) compared to patients with one (40 ± 7) or no mutation (42 ± 7). We found a total of 15 nucleotide variants (three new) in the 3′ UTR region. The frequency of carriers of the rare rs62637702 G allele (*94A/G) was significantly lower among the patients compared to healthy controls (n = 418) (0.03 vs. 0.004; p < 0.001), suggesting a protective role for this allele. In order to investigate the basal effect of this variant, we performed luciferase assays. No different basal activity was observed between the two alleles. In conclusion, the rs62637702 polymorphism was associated with PD. This could be a surrogate marker for disease risk, in linkage disequilibrium with other non-identified functional variant.

Niemann-Pick disease is a lysosomal storage disorder resulting from inherited deficiency in acid sphingomyelinase (ASM). Use of adeno-associated virus serotype 2 (AAV2) to deliver human acid sphingomyelinase (hASM) is currently being explored as a means to treat the devastating neurological features of NPD, which are refractory to traditional enzyme replacement therapy. In this study, we evaluated the long-term efficacy and safety of AAV2-hASM after direct infusion into the CNS of nonhuman primates. First, we confirmed the efficacy of AAV2-hASM in naive rats, which exhibited increased ASM expression and enzyme activity after infusion, without evidence of local or systemic toxicity. Next, the model was adapted to naive nonhuman primates (NHPs) with various doses of AAV2-hASM or saline delivered into the brainstem and both thalami. Strikingly, NHPs that received a high dose of AAV2-hASM displayed significant motor deficits that were not seen in low-dose animals in both the short-term (3-month) and long-term (9-month) treatment groups. In treated NHPs, ASM expression and activity were elevated with associated alterations in the sphingolipidomic profile in brain regions transduced with AAV2-hASM. Initial histological analysis indicated marked inflammatory reactions, and immunohistochemical analysis confirmed a robust inflammatory response. Importantly, pronounced upregulation of the chemokine CCL5, a target of ASM-mediated inflammatory signaling, was detected that correlated with the inflammatory response, providing a possible mechanism for hASM-associated toxicity. This study defines dose-dependent and dose-independent toxicities of AAV2-hASM in the naive primate brain, and reveals potential challenges in the design of a clinical trial.

Widespread distribution of gene products at clinically relevant levels throughout the CNS has been challenging. Adeno-associated virus type 9 (AAV9) vector has been reported as a good candidate for intravascular gene delivery, but low levels of preexisting antibody titers against AAV in the blood abrogate cellular transduction within the CNS. In the present study we compared the effectiveness of vascular delivery and cerebrospinal fluid (CSF) delivery of AAV9 in transducing CNS tissue in nonhuman primates. Both delivery routes generated similar distribution patterns, although we observed a more robust level of transduction after CSF delivery. Consistent with previous reports administering AAV9, we found greater astrocytic than neuronal tropism via both routes, although we did find a greater magnitude of CNS transduction after CSF delivery compared with intravascular delivery. Last, we have demonstrated that delivery of AAV9 into the CSF does not shield against AAV antibodies. This has obvious implications when developing and/or implementing any clinical trial studies.

Background and objective. Mutations in the Leucine-Rich Repeat Kinase 2 (LRRK2) gene at chromosome 12q12 are the most common genetic cause of sporadic and familial late-onset Parkinson's disease. Our aim was to identify novel LRRK2 mutations in late-onset Parkinson's disease families. Design. We analyzed chromosome 12p11.2-q13.1 haplotypes in 14 late-onset Parkinson's disease families without known LRRK2 mutations. Results. Haplotype analysis identified 12 families in which the affected subjects shared chromosome 12p11.2-q13.1 haplotypes. LRRK2 sequencing revealed a novel co-segregating missense mutation in exon 36 (c.5281A>C; p.S1761R) located within a highly conserved region of the COR [C-terminal of ROC (Ras of complex proteins)] domain wherein it could deregulate LRRK2 kinase activity by modifying ROC-COR dimer stability. p.S1761R was present in a late-onset Parkinson's disease family and in 2 unrelated Parkinson's disease subjects, but not in 2491 healthy controls. LRRK2 p.S1761R carriers developed levodopa-responsive asymmetrical parkinsonism, with variable age at onset (range: 37–72 years) suggesting age-dependent penetrance. These findings indicate that mutations interfering with LRRK2 ROC-COR domain dimerization lead to typical Parkinson's disease. © 2011 Movement Disorder Society

Alpha-synuclein gene (SNCA) polymorphisms have been associated with the common sporadic form of Parkinson’s disease (PD). We searched for DNA variants at the SNCA 3′ UTR through single strand conformation analysis and direct sequencing in a cohort of Spanish PD patients and controls. We have genotyped the rs356165 SNCA 3′ UTR polymorphism in a total of 1,135 PD patients and 772 healthy controls from two Spanish cohorts (Asturias and Navarre). We identified six SNCA 3′ UTR variants. Single nucleotide polymorphism (SNP) rs356165 was significantly associated with PD risk in the Spanish cohort (p = 0.0001; odd ratio = 1.37, 95%CI = 1.19–1.58). This SNP was also significantly associated with early age at onset of PD. Our work highlights rs356165 as an important determinant of the risk of developing PD and early age at onset and encourages future research to identify a functional effect on SNCA expression.

Background Isolated action tremor (IAT) is the hallmark clinical feature of essential tremor (ET), but it may also be a prominent feature of some individuals with Parkinson’s disease (PD) suggesting a pathogenic relationship between these two disorders. Objectives We investigated the integrity of the striatal presynaptic dopaminergic system in subjects presenting IAT to improve the diagnostic accuracy and to explore any putative relationships between ET and PD. Methods The striatal dopaminergic system was examined by means of dopamine transporter imaging using 123I-(fluoropropyl)-2s-carbomethoxy-3s-(4-iodophenyl) nortropane ([123I]-FP-CIT) single-photon emission tomography (DAT-SPECT) in a clinical series of individuals with IAT, excluding those with associated resting tremor and bradykinesia. Results Among 167 incidental individuals with IAT eligible for DAT-SPECT (Male/Female = 58.9/41.1%; Age = 67.8 ± 14.3 years), reduced striatal uptake was observed in 114 out of 167 (68.3%), whereas normal striatal binding was observed in the remaining 53 subjects (31.7%). Onset of tremor after 50 years and asymmetrical distribution of tremor were predictive variables of nigrostriatal denervation, whereas gender, family history and the presence of intentional, cephalic or voice tremors were not associated with nigrostriatal denervation. Conclusions Our findings suggest that IAT is a frequent presenting symptom in a subset of individuals with PD, often misdiagnosed as ET, and that DAT-SPECT can help differentiate between these two disorders. Current diagnostic criteria for ET should be revised to include asymmetry and late-onset tremor as predictors of nigrostriatal denervation.