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Introduction Neurodegeneration is known basis of several different Parkinson syndromes. The most common Parkinson syndrome is the Parkinson's disease. Distinction between different Parkinson syndromes is based on pathology or genetic findings. Recent studies indicate that several major variants of PS have some characteristics of a prion disease and may therefore be transmissible. Married couples offer a unique opportunity to study person-to-person transmission and the role of shared environments as the cause of parkinsonism. Methods Autopsy is offered to patients seen at the Movement Disorders Clinic Saskatchewan at no cost. Five couples seen in our clinic, where each spouse had a clinical diagnosis of parkinsonism, came to autopsy. Results Median duration of marriage was 42 years before the Parkinson syndrome first manifested in a spouse. Three couples were pathologically or genetically discordant for Parkinson variant. Each spouse in the other two couples had Parkinson's disease. One couple had onset separated by 20 years and one partner had a strong family history of Parkinson's disease. Conclusion Our data indicate that neither of the Parkinson's disease, Progressive Supranuclear Palsy and Multiple System Atrophy are transmitted by sexual or other intimate contact. The data also indicate against shared environments as the cause of these disorders.

Mutations in dynactin DCTN1 (p150(glued)) have previously been linked to familial motor neuron disease or Perry syndrome (PS) consisting of depression, parkinsonism and hypoventilation.We sequenced DCTN1 in 636 Caucasian patients with parkinsonism (Parkinson's disease and Parkinson-plus syndromes) and 508 healthy controls. Variants (MAF 0.01) were subsequently genotyped in Caucasian (1360 cases and 1009 controls) and Asian cohorts (1046 cases and 830 controls), and the functional implications of pathogenic variants were assessed.We identified 17 rare variants leading to non-synonymous amino-acid substitutions. Four of the variants were only observed in control subjects, four in both cases and controls and the remaining nine in cases only. One of the variants, DCTN1 p.K56R, was present in two patients with progressive supranuclear palsy (PSP) with a shared minimal 2.2 Mb haplotype. Both subjects have parkinsonism as the most prominent symptom with abnormal ocular movements, moderate cognitive impairment and little to no l-dopa response. Neither subject presents with depression, central hypoventilation or weight loss. For one of the subjects MRI shows symmetrical atrophy of temporal and frontoparietal lobes. In HEK293 cells mutant p150(glued) (p.K56R) shows less affinity for microtubules than wild-type, with a more diffuse cytoplasmic distribution.We have identified DCTN1 p.K56R in patients with PSP. This variant is immediately adjacent to the N-terminal p150(glued) 'CAP-Gly' domain, affects a highly conserved amino acid and alters the protein's affinity to microtubules and its cytoplasmic distribution.

Background Definite diagnosis of idiopathic Parkinson's disease is based on histological findings of marked substantia nigra neuronal loss and Lewy body inclusions. Almost all cases with clinical diagnosis of idiopathic Parkinson's disease are treated with levodopa. Because there is no biological marker for the diagnosis, erroneous clinical diagnosis and treatment of such cases with levodopa are well known. There is very limited literature on levodopa treated cases that had normal substantia nigra at autopsy. Methods Patients seen at Movement Disorders Clinic Saskatchewan are offered autopsy at no cost to the family/estate of the patient. Autopsy studies are performed by certified neuropathologists. Notation on the status of substantia nigra is made in every autopsied case. Results Between 1968 and 2014, 21 cases treated with levodopa had normal substantia nigra at autopsy. Eleven patients continued levodopa until death and 9 received the drug for four years or longer. No objective motor symptom benefit, dyskinesia or motor response fluctuations on levodopa were observed in any case. The most common final diagnosis was essential tremor. Conclusion Individuals with normal substantia nigra do not benefit from levodopa and do not manifest motor response fluctuations or dyskinesia. Long-term use of levodopa is not toxic to normal human substantia nigra.

Background Most of the literature on pathology of essential tremor (ET) has reported no consistent abnormalities. Some recent studies however indicate that cerebellar Purkinje cell (PC) loss is the pathological basis of ET in most patients. Objective To compare cerebellar PC loss in ET, with normal and tremor dominant Parkinson’s disease [PD] control brains. Methods Cerebellar PC counts were performed in seven ET, six PD and two normal control brains. Three different counting methods – sectioned through nucleolus, through nucleus and through any part of PC body, were used to count the PC. Results There were individual differences in the PC counts both in the ET and the PD cases. In all three subgroups, there was a reduction in the number of PC with advancing age. When the individuals of comparable age in the three subgroups were considered, there was no clear distinction between ET, PD and normal control subjects. There was no association between the degree of PC loss and the severity or the duration of ET. Conclusion Our study militates against the hypothesis that PC loss is pathognomonic of ET.

Up to 6% of the general population have essential tremor (ET). In a number of couples both partners may have ET. The clinical profile of ET in children and the parents where both parents and the child have ET remains to be established. We report on two families where both parents and one child have ET. The severity of ET was greater in the children than in either parent. Such families could provide special opportunity to determine relation between genotype and phenotypic expression of ET.

The pathophysiology of essential tremor (ET) is unknown but recent studies report that the majority of ET cases has cerebellar Purkinje cell (PC) degeneration and its sequelae. Objective To perform PC counts in ET, and normal and Parkinson's disease (PD) controls to determine the relationship of PC loss to ET. Methods All ET cases and PD controls were followed at our clinic. Normal controls had no history of neurological disease and had normal standard neuropathological studies. The PC counts were done by a neuropathologist who was blinded to the clinical diagnosis. Three different methods were used for counting PC; section through any part of the PC, through any part of the PC nucleus, and through any part of PC nucleolus. The counts were done in five non-contiguous microscopic fields. Results 59 brains were studied. These included 12 ET, 41 PD controls, and six normal controls. The mean age at death was 82.7 in ET, 79.1 in PD, and 75.7 years in the normal controls. The mean duration of symptoms was 34 years in ET and 15.7 years in the PD cases. The mean PC counts through any part of the neuron were 64.8 in ET, 56.2 in PD, and 58.0 in normal controls. Differences were not significant. Conclusion Cerebellar PC loss does not distinguish ET from controls. It is concluded that PC loss is neither a pathological basis for, nor the distinctive feature of ET.

The study of the neuropathological underpinnings of essential tremor (ET) is a relatively new undertaking. The purpose of this paper is three-fold. The first is to comment on methodological problems in a recently-published paper by Rajput et al, the major one being the small sample size of that study, which resulted in a Type II statistical error. Hence, one cannot conclude based on their data that there is no Purkinje cell (PC) loss in ET. Secondly, we comment on conceptual problems with that study, which suggested that PC loss might not be a featured characteristic of ET because it is also found in other disease states. We discuss why this is an erroneous conclusion. Our third purpose is to more broadly discuss the role of the cerebellum in ET, giving consideration to the wealth of clinical and postmortem data that have accumulated over recent years. In this discussion, we make the following points: (1) it is now generally recognized that ET is a disease of cerebellar systems dysfunction, (2) given the nature of the postmortem work, revealing the presence of several types of structural-anatomical changes within the cerebellum and absence of detectable changes in other brain regions, the most empirically-based explanation is that the primary problem in ET is in the cerebellum itself, (3) that the collection of cellular changes in the cerebellum in ET are also present in other cerebellar degenerations should add to rather than detract from the notion that ET is a disease of cerebellar degeneration.

Clinicogenetic and pathological studies have shown that mutations of the glucocerebrosidase gene (GBA) are a risk factor for Parkinson’s disease and Lewy body disorders. In the present study, we have identified GBA mutations in 6.8% (4/59) of cases with a pathological diagnosis of diffuse Lewy body disease. Taken with previous studies, it appears that GBA mutations are associated with a more diffuse pattern of Lewy body distribution involving the cerebral cortex than the brainstem/limbic distribution observed in typical Parkinson’s disease.

A functional variant in the Histamine N-Methyltransferase gene (HNMT – rs11558538) resulting in a threonine to isoleucine substitution (Thr105Ile), has been shown to impair histamine degradation. Two recent studies reported that the threonine allele of this polymorphism might be a risk factor for Parkinson disease (PD) and essential tremor (ET) development. Although PD and ET are considered different entities, they share some clinical and pathological features, suggesting a possible joint etiology. In this study we assess the role of the Thr105Ile variant in PD and ET development, genotyping the variant in a North American Caucasian PD and ET case-control series. Statistical analysis did not identify any significant association between this variant and PD or ET; therefore, our findings do not support the HNMT Thr105Ile variant as a factor in disease development or a genetic link between the disorders.

It has been proposed that there is an increased frequency of glucosidase-beta mutations in Lewy body disorders. Our comprehensive DNA sequencing approach found a small number of glucosidase-beta mutations in 101 neuropathologically defined Lewy body disease cases (3%) compared to 99 healthy post-mortem controls (1%); odds ratio 3.0 (95% CI: 0.3-29, p=0.3). All three affected carriers were classified as diffuse Lewy body disease (n=3/50; 6%). Our study suggests glucosidase-beta variants have a limited role in susceptibility to Lewy body disease in North America.

Multiple system atrophy (MSA) is by nature a ‘sporadic’ disease with no evidence of familial aggregation observed. However, the α-synuclein locus (SNCA) multiplication families have clinically displayed parkinsonism and autonomic dysfunction. The present study did not find any SNCA multiplications in a series of 58 pathologically confirmed MSA cases excluding this event as a common cause of MSA. The question of a genetic component in MSA remains to be answered.

The incidence of Parkinson syndrome in North America is 20.5/10(5), adjusted to 1970 US population, and there has been no significant change between 1935 and 1979. The composition of different Parkinson variants in the general population, however, has altered remarkably during recent decades. Arteriosclerotic Parkinsonism is very rarely diagnosed now, post-encephalitic Parkinsonism is extinct and drug induced Parkinsonism, first identified in the 1950s, is now the second most common variant in the combined community and institutionalised population survey. There has been a trend to higher incidence of Parkinson's disease in recent decades and it is predicted that the incidence would rise further if the current population survival trends continue. There is no race or gender difference for the risk of Parkinson's disease. Survival in Parkinson's disease has increased since the widespread use of levodopa. The prevalence rate of Parkinson syndrome in North America is estimated at 300/105. Increased risk of Parkinson's disease in essential tremor patients and the reported protective effect of smoking are artifactual. Twin studies show a concordance rate of 10.5% in monozygotic and 10.8% in dizygotic twins, indicating against a major genetic basis for Parkinson's disease. Several large Parkinson's disease families with autosomal dominant inheritance are well documented. In one such family, linkage to chromosome 4 is reported and mutation in the a-synuclein gene has been identified. In several other families, linkage to that region was not detected. These families are believed to inherit a Parkinson's disease susceptibility trait.