Clustering of motor and nonmotor traits in leucine-rich repeat kinase 2 G2019S Parkinson's disease nonparkinsonian relatives: A multicenter family study.

OBJECTIVES: The objective of this study was to determine phenotypic features that differentiate nonparkinsonian first-degree relatives of PD leucine-rich repeat kinase 2 (LRRK2) G2019S multiplex families, regardless of carrier status, from healthy controls because nonparkinsonian individuals in multiplex families seem to share a propensity to present neurological features. METHODS: We included nonparkinsonian first-degree relatives of LRRK2 G2019S familial PD cases and unrelated healthy controls participating in established multiplex family LRRK2 cohorts. Study participants underwent neurologic assessment including cognitive screening, olfaction testing, and questionnaires for daytime sleepiness, depression, and anxiety. We used a multiple logistic regression model with backward variable selection, validated with bootstrap resampling, to establish the best combination of motor and nonmotor features that differentiates nonparkinsonian first-degree relatives of LRRK2 G2019S familial PD cases from unrelated healthy controls. RESULTS: We included 142 nonparkinsonian family members and 172 unrelated healthy controls. The combination of past or current symptoms of anxiety (adjusted odds ratio, 4.16; 95% confidence interval, 2.01-8.63), less daytime sleepiness (adjusted odds ratio [1 unit], 0.90; 95% confidence interval, 0.83-0.97], and worse motor UPDRS score (adjusted odds ratio [1 unit], 1.4; 95% confidence interval, 1.20-1.67) distinguished nonparkinsonian family members, regardless of LRRK2 G2019S mutation status, from unrelated healthy controls. The model accuracy was good (area under the curve = 79.3%). CONCLUSIONS: A set of motor and nonmotor features distinguishes first-degree relatives of LRRK2 G2019S probands, regardless of mutation status, from unrelated healthy controls. Environmental or non-LRRK2 genetic factors in LRRK2-associated PD may influence penetrance of the LRRK2 G2019S mutation. The relationship of these features to actual PD risk requires longitudinal observation of LRRK2 familial PD cohorts. © 2018 International Parkinson and Movement Disorder Society.

Oculogyric crises: A review of phenomenology, etiology, pathogenesis, and treatment.

Oculogyric crises are a rare movement disorder characterized by paroxysmal, conjugate, tonic, usually upwards, deviation of the eyes. Causes for oculogyric crises are limited and include complications of dopamine-receptor blocking medications and neurometabolic disorders affecting dopamine metabolism, suggesting that an underlying hypodopaminergic state is important to the pathogenesis. Mimickers of oculogyric crises exist, and we propose diagnostic criteria to distinguish true oculogyric crises. Recognition of oculogyric crises is important for the diagnosis and appropriate treatment of rare disorders, and an approach to investigations in oculogyric crises is proposed. © 2017 International Parkinson and Movement Disorder Society.

Heart rate variability in leucine-rich repeat kinase 2-associated Parkinson's disease.

BACKGROUND: Heart rate variability is reduced in idiopathic PD, indicating cardiac autonomic dysfunction likely resulting from peripheral autonomic synucleinopathy. Little is known about heart rate variability in leucine-rich repeat kinase 2-associated PD. OBJECTIVES: This study investigated heart rate variability in LRRK2-associated PD. METHODS: Resting electrocardiograms were obtained from 20 individuals with LRRK2-associated PD, 37 nonmanifesting carriers, 48 related noncarriers, 26 idiopathic PD patients, and 32 controls. Linear regression modelling compared time and frequency domain values, adjusting for age, sex, heart rate, and disease duration. RESULTS: Low-frequency power and the ratio of low-high frequency power were reduced in idiopathic PD versus controls (P < .008, P < .029 respectively). In contrast, individuals with LRRK2-associated PD were not statistically different from controls in any parameter measured. Furthermore, all parameters trended toward being higher in LRRK2-associated PD when compared with idiopathic PD. CONCLUSIONS: Heart rate variability may remain intact in LRRK2-associated PD, adding to a growing literature supporting clinical-pathologic differences between LRRK2-associated and idiopathic PD. © 2017 International Parkinson and Movement Disorder Society.

Implications of nocturnal symptoms towards the early diagnosis of Parkinson's disease.

Nocturnal symptoms are frequent in Parkinson disease (PD) and consist of nocturnal sleep disorders such as REM sleep behavior disorder (RBD) and restless legs syndrome. There is an increasing need for reliable, early, pre-motor diagnosis of PD, since motor symptoms occur when there is already significant neuronal loss. Recent prospective studies have shown that over 80% of idiopathic RBD patients over time converted to PD and related synucleinopathies. RBD patients have autonomic, visual, and olfactory dysfunction as well as neuroimaging abnormalities similar to those seen in PD. Studies have shown that neuroimaging abnormalities and visual and olfactory dysfunction can help predict which RBD patients will likely convert to a neurodegenerative diagnosis within a short follow-up period. These factors make RBD an ideal population for prediction to PD conversion, allowing future testing and eventual use of neuroprotective strategies.

Dream Enactment Behavior Disorder Associated with Pallido-Nigro-Luysian Degeneration and Tau Proteinopathy.

BACKGROUND: Pallido-nigro-luysian atrophy (PNLA) is a rare neurodegenerative disorder with only a few cases reported to date. Although the clinical picture usually resembles progressive supranuclear palsy, pathological examination reveals more selective atrophy and loss of neurons in the globus pallidus, substantia nigra and subthalamic nucleus. OBJECTIVES: To describe the clinical features and pathological findings of a patient with PNLA. METHODS: Case report with clinico-pathological discussion. RESULTS: An 83-year-old man presented to our clinic with a vertical supranuclear gaze palsy, parkinsonism, gait impairment and sleep abnormalities suggestive of REM-sleep behavior disorder. Neuropathological examination 5 years after symptom onset revealed subcortical tau proteinopathy compatible with a PNLA pattern. There was also an associated mild degree of limbic/subcortical inflammatory response, Alzheimer's disease-related changes, as well as argyrophilic grain disease. CONCLUSIONS: We present a comprehensive clinico-pathological discussion of a patient with PNLA. Besides parkinsonism and vertical supranuclear gaze palsy, the patient also had a sleep disorder, clinically suggestive of REM behavioral disorder, which has not been previously reported in PNLA. We expand the clinical phenotype of this rare condition and provide neuropathological evidence for the associated abnormalities.

Differential susceptibility to excitotoxic stress in YAC128 mouse models of Huntington disease between initiation and progression of disease.

Huntington disease (HD) is a neurodegenerative disorder caused by an expanded CAG tract in the HD gene. Polyglutamine expansion of huntingtin (htt) results in early, progressive loss of medium spiny striatal neurons, as well as cortical neurons that project to the striatum. Excitotoxicity has been postulated to play a key role in the selective vulnerability of striatal neurons in HD. Early excitotoxic neuropathological changes observed in human HD brain include increased quinolinate (QUIN) concurrent with proliferative changes such as increased spine density and dendritic length. In later stages of the disease, degenerative-type changes are apparent, such as loss of dendritic arborization, a reduction in spine density and reduced levels of 3-hydroxykynurenine and QUIN. It is currently unknown whether sensitivity to excitotoxic stress varies between initiation and progression of disease. Here, we have assessed the excitotoxic phenotype in the YAC128 mouse model of HD by examining the response to excitotoxic stress at different stages of disease. Our results demonstrate that YAC128 mice display enhanced sensitivity to NMDA ex vivo and QUIN in vivo before obvious phenotypic changes. In contrast, 10-month-old symptomatic YAC128 mice are resistant to QUIN-induced neurotoxicity. These findings are paralleled by a significant increase in NMDAR-mediated membrane currents in presymptomatic YAC128 dissociated medium spiny neurons progressing to reduced NMDAR-mediated membrane currents with disease progression. These data highlight the dynamic nature of the mutant htt-mediated excitotoxic phenotype and suggests that therapeutic approaches to HD may need to be altered, depending on the stage and development of the disease.

To be or not to be toxic: aggregations in Huntington and Alzheimer disease.

Insoluble aggregated proteins in Alzheimer disease and Huntington disease might not be pathogenic. Human studies have poor correlations between aggregates and clinical disease or pathology in these disorders, whereas mouse models have demonstrated that neuronal loss can occur in the absence of detectable aggregates. Furthermore, aggregates can exist in the absence of disease pathology in mice or symptoms in humans. Recent research suggests that soluble protein fragments, not insoluble aggregated proteins, are the toxic species in these disorders.

Investigating Voice as a Biomarker for Leucine-Rich Repeat Kinase 2-Associated Parkinson's Disease.

We investigate the potential association between leucine-rich repeat kinase 2 (LRRK2) mutations and voice. Sustained phonations ('aaah' sounds) were recorded from 7 individuals with LRRK2-associated Parkinson's disease (PD), 17 participants with idiopathic PD (iPD), 20 non-manifesting LRRK2-mutation carriers, 25 related non-carriers, and 26 controls. In distinguishing LRRK2-associated PD and iPD, the mean sensitivity was 95.4% (SD 17.8%) and mean specificity was 89.6% (SD 26.5%). Voice features for non-manifesting carriers, related non-carriers, and controls were much less discriminatory. Vocal deficits in LRRK2-associated PD may be different than those in iPD. These preliminary results warrant longitudinal analyses and replication in larger cohorts.

Actigraphy Detects Greater Intra-Individual Variability During Gait in Non-Manifesting LRRK2 Mutation Carriers.

BACKGROUND: With recent advances in the search for disease-modifying therapies for Parkinson's disease (PD) the importance of identifying prodromal markers becomes greater. Non-manifesting LRRK2 mutation carriers (NMC) are at risk for developing PD, and provide a population in which to identify possible markers. OBJECTIVE: The aim of this study was to test the hypothesis that NMC have differences in daily activity, fragmentation of sleep, arm swing asymmetry, and movement variability during walking, detectable by actigraphy, as compared to matched control subjects. METHODS: Eleven NMC, fourteen PD patients (4 LRRK2-PD, 10 idiopathic PD (iPD)), and twenty-nine controls wore wristbands containing an accelerometer for seven days, and performed a daily walking task. Outcome measures included daily activity, fragmentation of activity, fragmentation of sleep, arm swing asymmetry during walking, and intra-individual variability. RESULTS: Compared to healthy controls, both NMC and LRRK2/iPD showed higher intra-individual variability in activity during walking compared to healthy controls. Individuals with LRRK2-PD/iPD, but not NMC, tend to have lower activity levels, more arm swing asymmetry and less increase of arm swing with transition from slow to faster walking speed compared to healthy controls. CONCLUSION: Higher intra-individual variability of gait-associated movements might be a useful biomarker of prodromal PD. These results encourage replication in a larger sample and longitudinal analysis is warranted.

Cognitive dysfunction precedes neuropathology and motor abnormalities in the YAC128 mouse model of Huntington's disease.

Huntington's disease (HD) is an adult-onset neurodegenerative disorder involving motor dysfunction, cognitive deficits, and psychiatric disturbances that result from underlying striatal and cortical dysfunction and neuropathology. The YAC128 mouse model of HD reproduces both the motor deficits and selective degeneration observed in the human disease. However, the presence of cognitive impairment in this model has not been determined. Here, we report mild cognitive deficits in YAC128 mice that precede motor onset and progressively worsen with age. Rotarod testing revealed a motor learning deficit at 2 months of age that progresses such that by 12 months of age, untrained YAC128 mice are unable to learn the rotarod task. Additional support for cognitive dysfunction is evident in a simple swimming test in which YAC128 mice take longer to find the platform than wild-type (WT) controls beginning at 8 months of age. YAC128 mice also have deficits in open-field habituation and in a swimming T-maze test at this age. Strikingly, in the reversal phase of the swimming T-maze test, YAC128 mice take twice as long as WT mice to locate the platform, indicating a difficulty in changing strategy. At 12 months of age, YAC128 mice show decreased prepulse inhibition and habituation to acoustic startle. The clear pattern of cognitive dysfunction in YAC128 mice is similar to the symptoms and progression of cognitive deficits in human HD and provides both the opportunity to examine the relationship between cognitive dysfunction, motor impairment, and neuropathology in HD and to assess whether potential therapies for HD can restore cognitive function.

Levels of mutant huntingtin influence the phenotypic severity of Huntington disease in YAC128 mouse models.

Huntington disease (HD) is a devastating neuropsychiatric disease caused by expansion of a trinucleotide repeat (CAG) in the HD gene. Neuropathological changes include the appearance of N-terminal huntingtin fragments, decreased brain weight and apoptotic neuronal loss in a select subset of neurons located in the striatum. There is still controversy over whether homozygosity for the mutation in HD is associated with a more severe phenotype. In humans, resolution of this issue has been complicated by the small number of homozygous patients and difficulty in the definition of reliable phenotypic endpoints. In order to definitively determine whether there is a correlation between phenotypic severity and expression levels of mutant huntingtin, we undertook a behavioral and neuropathological assessment of YAC128 mice with varying levels of mutant huntingtin. The results reveal a clear relationship between levels of mutant huntingtin and phenotype defined by earlier age of onset, more rapid progression, enhanced striatal volume loss, acceleration of nuclear huntingtin fragment accumulation and increased sensitivity to NMDAR-mediated excitotoxicity. These results provide clear evidence in vivo supporting a more severe phenotype associated with increased levels of mutant huntingtin as seen in homozygotes for HD.

Elevated brain 3-hydroxykynurenine and quinolinate levels in Huntington disease mice.

The brain levels of the endogenous excitotoxin quinolinic acid (QUIN) and its bioprecursor, the free radical generator 3-hydroxykynurenine (3-HK), are elevated in early stage Huntington disease (HD). We now examined the status of these metabolites in three mouse models of HD. In R6/2 mice, 3-HK levels were significantly and selectively elevated in the striatum, cortex and cerebellum starting at 4 weeks of age. In contrast, both 3-HK and QUIN levels were increased in the striatum and cortex of the full-length HD models, beginning at 8 months (YAC128) and 15 months (Hdh(Q92) and Hdh(Q111)), respectively. No changes were seen in 13-month-old shortstop mice, which show no signs of motor or cognitive dysfunction or selective neuropathology. These results demonstrate both important parallels and intriguing differences in the progressive neurochemical changes in these HD mouse models and support the hypothesis that QUIN may play a role in the striatal and cortical neurodegeneration of HD.

Cleavage at the caspase-6 site is required for neuronal dysfunction and degeneration due to mutant huntingtin.

Cleavage of huntingtin (htt) has been characterized in vitro, and accumulation of caspase cleavage fragments represents an early pathological change in brains of Huntington's disease (HD) patients. However, the relationship between htt proteolysis and the pathogenesis of HD is unknown. To determine whether caspase cleavage of htt is a key event in the neuronal dysfunction and selective neurodegeneration in HD, we generated YAC mice expressing caspase-3- and caspase-6-resistant mutant htt. Mice expressing mutant htt, resistant to cleavage by caspase-6 but not caspase-3, maintain normal neuronal function and do not develop striatal neurodegeneration. Furthermore, caspase-6-resistant mutant htt mice are protected against neurotoxicity induced by multiple stressors including NMDA, quinolinic acid (QA), and staurosporine. These results are consistent with proteolysis of htt at the caspase-6 cleavage site being an important event in mediating neuronal dysfunction and neurodegeneration and highlight the significant role of htt proteolysis and excitotoxicity in HD.

Selective degeneration and nuclear localization of mutant huntingtin in the YAC128 mouse model of Huntington disease.

Huntington disease (HD) is an adult onset neurodegenerative disorder that predominantly affects the striatum and cortex despite ubiquitous expression of mutant huntingtin (htt). Here we demonstrate that this pattern of selective degeneration is present in the YAC128 mouse model of HD. At 12 months, YAC128 mice show significant atrophy in the striatum, globus pallidus and cortex with relative sparing of the hippocampus and cerebellum (striatum: -10.4%, P<0.001; globus pallidus: -10.8%, P=0.04; cortex: -8.6%, P=0.001; hippocampus: +0.3%, P=0.9; cerebellum: +2.9%, P=0.6). Similarly, neuronal loss at this age is present in the striatum (-9.1%, P<0.001) and cortex of YAC128 mice (-8.3%, P=0.02) but is not detected in the hippocampus (+1.5%, P=0.72). Mutant htt expression levels are similar throughout the brain and fail to explain the selective neuronal degeneration. In contrast, nuclear detection of mutant htt occurs earliest and to the greatest extent in the striatum-the region most affected in HD. The appearance of EM48-reactive mutant htt in the nucleus in the striatum at 2 months coincides with the onset of behavioral abnormalities in YAC128 mice. In contrast to YAC128 mice, the R6/1 mouse model of HD, which expresses exon 1 of mutant htt, exhibits non-selective, widespread atrophy along with non-selective nuclear detection of mutant htt at 10 months of age. Our findings suggest that selective nuclear localization of mutant htt may contribute to the selective degeneration in HD and that appropriately regulated expression of full-length mutant htt in YAC128 mice results in a pattern of degeneration remarkably similar to human HD.

Absence of behavioral abnormalities and neurodegeneration in vivo despite widespread neuronal huntingtin inclusions.

We have serendipitously established a mouse that expresses an N-terminal human huntingtin (htt) fragment with an expanded polyglutamine repeat (approximately 120) under the control of the endogenous human promoter (shortstop). Frequent and widespread htt inclusions occur early in shortstop mice. Despite these inclusions, shortstop mice display no clinical evidence of neuronal dysfunction and no neuronal degeneration as determined by brain weight, striatal volume, and striatal neuronal count. These results indicate that htt inclusions are not pathogenic in vivo. In contrast, the full-length yeast artificial chromosome (YAC) 128 model with the identical polyglutamine length and same level of transgenic protein expression as the shortstop demonstrates significant neuronal dysfunction and loss. In contrast to the YAC128 mouse, which demonstrates enhanced susceptibility to excitotoxic death, the shortstop mouse is protected from excitotoxicity, providing in vivo evidence suggesting that neurodegeneration in Huntington disease is mediated by excitotoxic mechanisms.

Selective striatal neuronal loss in a YAC128 mouse model of Huntington disease.

An expanded CAG repeat is the underlying genetic defect in Huntington disease, a disorder characterized by motor, psychiatric and cognitive deficits and striatal atrophy associated with neuronal loss. An accurate animal model of this disease is crucial for elucidation of the underlying natural history of the illness and also for testing experimental therapeutics. We established a new yeast artificial chromosome (YAC) mouse model of HD with the entire human HD gene containing 128 CAG repeats (YAC128) which develops motor abnormalities and age-dependent brain atrophy including cortical and striatal atrophy associated with striatal neuronal loss. YAC128 mice exhibit initial hyperactivity, followed by the onset of a motor deficit and finally hypokinesis. The motor deficit in the YAC128 mice is highly correlated with striatal neuronal loss, providing a structural correlate for the behavioral changes. The natural history of HD-related changes in the YAC128 mice has been defined, demonstrating the presence of huntingtin inclusions after the onset of behavior and neuropathological changes. The HD-related phenotypes of the YAC128 mice show phenotypic uniformity with low inter-animal variability present, which together with the age-dependent striatal neurodegeneration make it an ideal mouse model for the assessment of neuroprotective and other therapeutic interventions.