Rapidly progressive autosomal dominant parkinsonism and dementia with pallido-ponto-nigral degeneration

Comparison of extent of tau pathology in patients with frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17), frontotemporal lobar degeneration with Pick bodies and early onset Alzheimer's disease

In order to gain insight into the pathogenesis of frontotemporal lobar degeneration (FTLD), the mean tau load in frontal cortex was compared in 34 patients with frontotemporal dementia linked to chromosome 17 (FTDP-17) with 12 different mutations in the tau gene (MAPT), 11 patients with sporadic FTLD with Pick bodies and 25 patients with early onset Alzheimer's disease (EOAD). Tau load was determined, as percentage of tissue occupied by stained product, by image analysis of immunohistochemically stained sections using the phospho-dependent antibodies AT8, AT100 and AT180. With AT8 and AT180 antibodies, the amount of tau was significantly (P < 0.001 in each instance) less than that in EOAD for both FTDP-17 (8.5% and 10.0% respectively) and sporadic FTLD with Pick bodies (16.1% and 10.0% respectively). With AT100, the amount of tau detected in FTDP-17 was 54% (P < 0.001) of that detected in EOAD, but no tau was detected in sporadic FTLD with Pick bodies using this particular antibody. The amount of insoluble tau deposited within the brain in FTDP-17 did not depend in any systematic way upon where the MAPT mutation was topographically located within the gene, or on the physiological or structural change generated by the mutation, regardless of which anti-tau antibody was used. Not only does the amount of tau deposited in the brain differ between the three disorders, but the pattern of phosphorylation of tau also varies according to disease. These findings raise important questions relating to the role of aggregated tau in neurodegeneration - whether this represents an adaptive response which promotes the survival of neurones, or whether it is a detrimental change that directly, or indirectly, brings about the demize of the affected cell.

Speech characteristics of patients with pallido-ponto-nigral degeneration and their application to presymptomatic detection in at-risk relatives

PURPOSE

This report describes the speech characteristics of individuals with a neurodegenerative syndrome called pallido-ponto-nigral degeneration (PPND) and examines the speech samples of at-risk, but asymptomatic, relatives for possible preclinical detection.

METHOD

Speech samples of 9 members of a PPND kindred were subjected to perceptual characterization. Speech deterioration patterns were reported for 2 participants followed longitudinally at 6-month intervals. Cross-sectional findings were reported for 3 participants at various stages of disease. Longitudinal and cross-sectional findings were used to guide the examination of 4 at-risk, but asymptomatic, participants.

RESULTS

Results revealed a progressive mixed dysarthria with hypokinetic, spastic, and flaccid features. It was characterized primarily by vocal tremor and high-frequency vocal flutter, speaking rate abnormalities most often in the direction of slowing, and a tendency toward monopitch. Dysarthria progression was marked by exacerbation and increasing severity of early features, progressive decrease in spontaneous speech output, verbal perseverations, and eventual mutism. Results for at-risk participants revealed preclinical speech abnormalities that preceded other motor signs. Speech results were examined in light of available autopsy findings for site of lesion associations.

CONCLUSION

The dysarthria of PPND is an early harbinger of disease onset. It has a mixed presentation, with hypokinetic, spastic, and flaccid features.

An immunohistochemical study of cases of sporadic and inherited frontotemporal lobar degeneration using 3R- and 4R-specific tau monoclonal antibodies

The pathological distinctions between the various clinical and pathological manifestations of frontotemporal lobar degeneration (FTLD) remain unclear. Using monoclonal antibodies specific for 3- and 4-repeat isoforms of the microtubule associated protein, tau (3R- and 4R-tau), we have performed an immunohistochemical study of the tau pathology present in 14 cases of sporadic forms of FTLD, 12 cases with Pick bodies and two cases without and in 27 cases of familial FTLD associated with 12 different mutations in the tau gene (MAPT), five cases with Pick bodies and 22 cases without. In all 12 cases of sporadic FTLD where Pick bodies were present, these contained only 3R-tau isoforms. Clinically, ten of these cases had frontotemporal dementia and two had progressive apraxia. Only 3R-tau isoforms were present in Pick bodies in those patients with familial FTLD associated with L266V, Q336R, E342V, K369I or G389R MAPT mutations. Patients with familial FTLD associated with exon 10 N279K, N296H or +16 splice site mutations showed tau pathology characterised by neuronal neurofibrillary tangles (NFT) and glial cell tangles that contained only 4R-tau isoforms, as did the NFT in P301L MAPT mutation. With the R406W mutation, NFT contained both 3R- and 4R-tau isoforms. We also observed two patients with sporadic FTLD, but without Pick bodies, in whom the tau pathology comprised only of 4R-tau isoforms. We have therefore shown by immunohistochemistry that different specific tau isoform compositions underlie the various kinds of tau pathology present in sporadic and familial FTLD. The use of such tau isoform specific antibodies may refine pathological criteria underpinning FTLD.

Functional Genomics meets neurodegenerative disorders

The transcriptomic and proteomic techniques presented in part I (Functional Genomics meets neurodegenerative disorders. Part I: transcriptomic and proteomic technology) of this back-to-back review have been applied to a range of neurodegenerative disorders, including Huntington's disease (HD), Prion diseases (PrD), Creutzfeldt-Jakob disease, amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), frontotemporal dementia (FTD) and Parkinson's disease (PD). Samples have been derived either from human brain and cerebrospinal fluid, tissue culture cells or brains and spinal cord of experimental animal models. With the availability of huge data sets it will firstly be a major challenge to extract meaningful information and secondly, not to obtain contradicting results when data are collected in parallel from the same source of biological specimen using different techniques. Reliability of the data highly depends on proper normalization and validation both of which are discussed together with an outlook on developments that can be anticipated in the future and are expected to fuel the field. The new insight undoubtedly will lead to a redefinition and subdivision of disease entities based on biochemical criteria rather than the clinical presentation. This will have important implications for treatment strategies.

Phenotypic heterogeneity within a new family with theMAPT p301s mutation

Mutations in the gene encoding the microtubule-associated protein tau (MAPT) cause frontotemporal dementia and parkinsonism linked to chromosome 17. Clinical variability is seen not only among families with different mutations, but also among family members with the same mutation. We investigated a newly identified familial frontotemporal dementia and parkinsonism family. The disease was of early onset and was inherited as an autosomal dominant trait. Clinically, parkinsonism was the prominent and often early feature, and it preceded dementia. Three autopsied cases shared involvement predominantly in the frontal and temporal lobes and also in the subcortical nuclei, including substantia nigra, globus pallidus, and subthalamic nucleus, that microscopically consisted of neuronal loss, microvacuolation, and astrocytic fibrosis. Immunohistochemistry demonstrated neuropil threads, ballooned cells, and glial fibrillary tangles. Sequencing analysis of the MAPT gene showed an alteration in one allele, resulting in a P301S substitution. These findings suggest that the MAPT P301S mutation can cause pathologically subcortical-predominant, neuropil thread-rich, tau-containing lesions, which could result in consistent parkinsonism. Our study confirms the notion that the phenotype observed in affected individuals from P301S MAPT mutation families is heterogeneous and is broader than the phenotypes seen to date in affected family members carrying other MAPT mutations.

Transgenic animal models of Alzheimer's disease and related disorders: histopathology, behavior and therapy

Alzheimer's disease (AD) is a devastating neurodegenerative disease that affects more than 15 million people worldwide. Within the next generation, these numbers will more than double. To assist in the elucidation of pathogenic mechanisms of AD and related disorders, such as frontotemporal dementia (FTDP-17), genetically modified mice, flies, fish and worms were developed, which reproduce aspects of the human histopathology, such as beta-amyloid-containing plaques and tau-containing neurofibrillary tangles (NFT). In mice, the tau pathology caused selective behavioral impairment, depending on the distribution of the tau aggregates in the brain. Beta-amyloid induced an increase in the numbers of NFT, whereas the opposite was not observed in mice. In beta-amyloid-producing transgenic mice, memory impairment was associated with increased levels of beta-amyloid. Active and passive beta-amyloid-directed immunization caused the removal of beta-amyloid plaques and restored memory functions. These findings have since been translated to human therapy. This review aims to discuss the suitability and limitations of the various animal models and their contribution to an understanding of the pathophysiology of AD and related disorders.

Parkinson's syndrome associated with neurofibrillary degeneration and tau pathologic findings

Several distinct clinical syndromes presenting with parkinsonism have been associated with subcortical neurofibrillary degeneration and the abnormal accumulation of hyperphosphorylated tau protein in the brain. Mutations of tau have been linked with a small number of autosomal dominantly inherited families who present with frontolimbic cognitive deficits, behavioural disorders, and Parkinson's syndrome. Some of the sporadic disorders (progressive supranuclear palsy [PSP] and corticobasal degeneration) have been referred to by molecular pathologists as primary tauopathies, implicating abnormalities of tau in their pathogenesis. We have identified a sporadic parkinsonian syndrome characterised by bradykinesia, a variable response to levodopa, and a mean duration of disease of 9 years, which resembles bodig (Parkinson's-dementia of Guam), and histologically has close similarities with both PSP and postencephalitic parkinsonism. Further characterisation of these cases frequently confused with Parkinson's disease may broaden the clinical spectrum of parkinsonian disorders linked with neurofibrillary tangle formation.

Early and pre-symptomatic neuropsychological dysfunction in the PPND family with the N279K tau mutation

The N279K mutation on the tau gene of chromosome 17 leads to an inherited condition that involves pallido-ponto-nigral degeneration (PPND). Patients with PPND develop dementia, but the pattern and onset of cognitive dysfunction has not yet been delineated. Four affected patients underwent neurocognitive evaluation within the first 2 years of PPND motor onset; one of whom underwent five serial neurocognitive evaluations, and another who was not diagnosed with PPND until the third annual evaluation. Impaired letter fluency was found in the early stages of PPND and was also shown to precede the onset of motor symptoms by 2 years. Trail Making A (visual scanning and motor speed) and Trail Making B (divided attention) were impaired within the first 2 years of the disease in all but one patient, but this individual showed clinically significant decline on these tasks by the third year of the disease. Learning, memory, and timed visuospatial sequencing skills were variably affected. Results reveal disproportionate frontal-executive dysfunction early in PPND disease course, a pattern similar to what has been reported in other FTDP-17 kindreds and in sporadic PSP. In addition, results suggest that letter fluency may be a sensitive predictor of incipient PPND.

Phenotypic presentation of frontotemporal dementia with Parkinsonism-chromosome 17 type P301S in a patient of Jewish-Algerian origin

A 39-year-old old Jewish woman of Algerian origin developed a rapidly progressive neurocognitive disorder characterized by asymmetric rigidity, spasticity with bilateral Babinski's sign, bradykinesia, altered speech that progressed to mutism, and severe bradyphrenia. She partially responded to levodopa. The family history revealed 4 affected first-degree relatives (3 had already died). Genetic studies carried out in the proband and her living affected sister showed a P301S mutation in chromosome 17.

Clinical-electrophysiological correlation of tremor and myoclonus in a kindred with the N279K tau mutation

We used electrophysiological methods to study the hyperkinetic movement disorders in a pallido-ponto-nigral degeneration (PPND) family, which harbors the N279K tau gene mutation. Our purpose was to: (1). characterize the tremor patterns, (2). characterize the myoclonus physiology, (3). determine whether electrophysiology can detect abnormalities in asymptomatic cases. In PPND, we found that the activation tremors correlated with a semi-rhythmic 6-10 Hz electromyography (EMG) pattern, and the rest tremors showed a reciprocal 4-6 Hz pattern. At least two different myoclonus physiology patterns exist in PPND, most notably contrasted by the presence or absence of a demonstrable electroencephalography (EEG) correlate. Electrophysiology yielded remarkable findings in those asymptomatic at-risk individuals that carried the N279K tau mutation.

State of the art review: molecular diagnosis of inherited movement disorders. Movement Disorders Society task force on molecular diagnosis

This review is designed to provide practical help for the clinical neurologist to make appropriate use of the possibilities of molecular diagnosis of inherited movement disorders. Huntington's disease, Parkinson's disease and parkinsonian syndromes, ataxias, Wilson disease, essential tremor, dystonias, and other genetic diseases associated with a variety of movement disorders are considered separately.

Gene therapy for Parkinson's disease: current status and future potential

Parkinson's disease appears to be a good candidate for gene therapy. The primary biochemical defect associated with the disease has been clearly determined as an absence of dopamine in the caudate-putamen, and the anatomical region where the neuropathologic hallmark of the disease, death of the nigral dopamine-producing neurons, occurs, remains circumscribed. Based on the biochemical and anatomical information gathered on Parkinson's disease, different gene therapy strategies have been devised to treat it. The first, and most explored strategy so far, consists in engineering cells to produce levodopa or dopamine so they will replace dopaminergic neurotransmission. Several types of cells have been employed in these experiments, and behavioral recovery has been reported in animal models of the disease. However, this approach cannot prevent neuronal death, nor reconstruct brain circuits. Another strategy is to protect cells by transferring genes that encode neurotrophic factors. Effort is now being concentrated into this research area, and promising results have recently been reported. Finally, an additional strategy aims at generating cells with a dopaminergic phenotype so they will be capable of replacing the missing dopaminergic neurons in biochemical, anatomical and functional terms. This has the potential to become an important constituent for an effective cure. Gene therapy holds significant promise for the treatment of neurodegenerative disorders, and Parkinson's disease treatment will benefit greatly from the knowledge and information arising from gene therapy research.

Physiologic assessment of autonomic dysfunction in pallidopontonigral degeneration with N279K mutation in the tau gene on chromosome 17

Autonomic function was investigated in five affected and five at-risk members of a single kinship of pallidopontonigral degeneration (PPND), which is a progressive syndrome of parkinsonism and frontotemporal dementia resulting from a mutation in the N279K tau gene on chromosome 17. Affected subjects reported symptoms including hyperhidrosis, sialorrhea, urinary frequency or incontinence, thermal intolerance, male sexual dysfunction, lacrimation, and dryness of the eyes or mouth. None had orthostatic hypotension. Autonomic testing revealed mild-to-moderate abnormalities in all five affected subjects and minor abnormalities in the three oldest, asymptomatic, at-risk subjects. Findings in affected subjects consisted of preganglionic sudomotor dysfunction in all five, impaired cardiovagal function in three, and reduced or absent pupillary near responses in four. Tests of adrenergic function were normal in all subjects. The degree of autonomic dysfunction correlated significantly with disease duration and with indices of disease severity. In conclusion, there is evidence in PPND of a disturbance in the central autonomic network.

Progressive supranuclear palsy: clinical and genetic aspects

PURPOSE OF THE REVIEW

This review focuses on the recent additions to the literature in the clinical and genetic aspects of progressive supranuclear palsy.

RECENT FINDINGS

Clinical features of progressive supranuclear palsy are reasonably well established and known to be quite characteristic. Recent epidemiological studies suggest that the disorder is more common than previously considered and that it is frequently misdiagnosed. New laboratory and novel imaging techniques are being tested and cerebrospinal fluid levels of tau protein have been found helpful in diagnosis. Pathological and biochemical studies in progressive supranuclear palsy brains have shown the predominance of hyperphosphorylated tau isoforms which contain the sequence encoded by exon 10 (4R) aggregated into filaments. Familial tauopathies linked to tau gene mutations showing clinical and neuropathological overlap with sporadic progressive supranuclear palsy have been described. Despite recent discoveries of the strong genetic association of sporadic progressive supranuclear palsy with tau gene polymorphisms, a specific risk allele for developing the palsy has not yet been identified yet.

SUMMARY

Recent clinical studies and clinicopathological correlations are contributing significantly to the delineation of the clinical features of progressive supranuclear palsy. These features and the appropriate use of laboratory tests allow for an earlier identification of the disease and a more accurate premortem diagnosis. However, no specific biological markers for the disorder are available yet, and consequently diagnosis in the early stages or when some of the characteristic signs and symptoms are missing, remains a major challenge. Despite the recent advances in the understanding of genetic factors involved in progressive supranuclear palsy, the cause of the disease still remains unknown. Biochemical studies in brains from progressive supranuclear palsy patients provide a potential helpful instrument to improve the characterization of this disorder.

Genetics of parkinsonism

Parkinson's disease (PD) was noted to have a familial component as early as 1880 (Leroux, 1880). More recently, the discovery of several genetic factors influencing parkinsonism has emphasized the importance of heredity in PD. The clinical spectrum of familial parkinsonism is wide; it includes not only PD, but also dementia with Lewy bodies (DLB), progressive supranuclear palsy (PSP), essential tremor, and other disorders. In the general population, it is likely that PD results from combined genetic and environmental factors, most of which are not yet known. The discovery of causal mutations in the gene for alpha-synuclein, parkin, and of genetic linkages to chromosomes 2p4, 4p5, and three loci on 1q6-8 have revolutionized PD research. This review focuses on recent progress in the Mendelian genetics of PD and those diseases in which parkinsonism is a prominent feature, and considers how these discoveries modify our beliefs regarding the etiology and pathogenesis of these disorders.

Genetics of dementia

Many neurodegenerative diseases are exceedingly complex disorders (Fig. 6). In the past decade, we have made tremendous advances in our understanding [figure: see text] of the genetic basis of these disorders. One common characteristic of these disorders is the existence of rare families in which a given disease is inherited as a Mendelian trait. In this article, we have reviewed the genetics of several common neurodegenerative disorders that are associated with cognitive disturbances and for which causative genes have been identified. Further genetic analysis should clarify the roles of known genes in the pathogenesis of common sporadic forms of these various diseases. Investigation of the normal and aberrant functions of these genes should provide insight into the underlying mechanisms of these disorders. Such research should facilitate new strategies for therapeutic interventions. Although molecular genetics has helped to clarify the etiology of these disorders, clinicians have played a critical role in the careful identification and classification of many families who were involved in the eventual mapping and cloning of causative mutations. The role of the clinician should not be underestimated. Future clinical and molecular genetics findings hold many clinical implications. It is likely that new diagnostic and therapeutic strategies for dementing disorders are just on the horizon.

Clinical features of frontotemporal dementia due to the intronic tau 10(+16) mutation

OBJECTIVE

To describe the clinical features of nine British families with neuropathologically verified frontotemporal dementia (FTD) due to the intronic tau exon 10(+16) mutation.

METHODS

Retrospective chart reviews of family members with FTD belonging to nine tau 10(+16) mutation pedigrees in whom neuropathologic examination had been carried out. APOE genotype was determined for those patients for whom DNA was available.

RESULTS

The median age at onset was 50 years (range 37 to 59 years; n = 30). The median age at death was 61 years (range 42 to 72 years; n = 33). The median duration of the disease was 11 years (range 3 to 22 years; n = 25) for those who have died and is 17 years (range 15 to 23 years; n = 3) for those living. The most common presenting symptom was disinhibition (n = 23). A minority presented with frontal dysexecutive symptoms, apathy, impairment of episodic memory, or depression. All of these patients subsequently developed personality and behavioral change. Memory impairment, language deficits, ritualistic behavior, hyperphagia, and hyperorality were frequent symptoms. Parkinsonism, neuroleptic sensitivity, or primitive reflexes were present in half of the patients, where these data were available. The clinical features of ALS were absent. Neuropathologic examination of 12 patients demonstrated the hallmark tau-positive neuronal and glial inclusions. APOE genotype did not account for the considerable variation in age at onset, age at death, duration of disease, or severity of estimated brain atrophy.

CONCLUSIONS

All cases fulfilled the clinical criteria for a diagnosis of FTD. Despite similar clinical phenotypes, there was considerable variation in age at onset and duration of disease both between and within families, suggesting the presence of an effect due to other genetic or environmental factors.

Inherited frontotemporal dementia in nine British families associated with intronic mutations in the tau gene

Genetic screening of 171 patients with frontotemporal lobar degeneration disclosed 14 patients, across nine pedigrees, with mutations in the intron to exon 10 in the tau gene, a region regulating the splicing of exon 10 via a stem loop mechanism. Thirteen of these patients had the +16 splice site mutation and one had the +13 splice site mutation. Affected members of all nine families presented with changes in behaviour and social conduct that were prototypical of frontotemporal dementia (FTD). In all patients with the +16 splice site mutation, the behavioural profile was characterized by disinhibition, restless overactivity, a fatuous affect, puerile behaviour and verbal and motor stereotypies. The single patient with the +13 mutation presented a contrasting picture of apathy and inertia. In addition, all patients had evidence of semantic loss. Pathologically, five of the six patients so far autopsied shared frontotemporal atrophy with involvement of the substantia nigra. The underlying histology was that of microvacuolar-type cortical degeneration with a few swollen cells. Tau pathology was widespread throughout the brain and present in neurones and glial cells, mostly in the frontal and temporal cortical regions. This was in the form of neurofibrillary tangles and amorphous tau deposits (pre-tangles); Pick bodies were not observed. Ultrastructurally, the tau filaments had a twisted, ribbon-like morphology distinct from the paired helical filaments of Alzheimer's disease. One patient died from an unrelated illness whilst in the early clinical stages of FTD. In this patient, cortical microvacuolar and astrocytic changes were absent, though there were scattered neurones and glial cells, immunoreactive to tau, throughout the cortical and subcortical regions. The disease process underlying the neurodegeneration within these inherited forms of FTD may therefore stem directly from early, primary alterations in the function of tau. All eight families with the +16 mutation seem to be part of a common extended pedigree, possibly originating from a founder member residing within the North Wales region of Great Britain.

Two large British kindreds with familial Parkinson's disease: a clinico-pathological and genetic study

We present the findings of a study of two large unrelated kindreds with autosomal dominant Parkinson's disease. The affected members were assessed clinically and with [(18)F]6-fluorodopa-PET and were indistinguishable from patients with the sporadic form of Parkinson's disease. In one kindred, an affected member was examined subsequently at autopsy and Lewy bodies were present in a distribution typical of sporadic Parkinson's disease. These kindreds are distinct from other Parkinsonian kindreds with identified genetic loci (PARK1-4) and provide further evidence for genetic heterogeneity in familial Parkinson's disease.

Novel observations with FDOPA-PET imaging after early nigrostriatal damage

Striatal 6-[18F]fluoro-L-DOPA (FDOPA) kinetic rate constants were measured by positron emission tomography (PET) in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated squirrel monkeys. After scanning, stereological counts of dopaminergic neurons were done in substantia nigra, and dopamine (DA) and metabolite concentrations were determined in the caudate, putamen, and substantia nigra. Graded doses of MPTP produced animals with mild to moderate reductions (10-35%) in dopaminergic neurons, where the percent of cell loss was proportional to the amount of MPTP given. Striatal DA and metabolite concentrations were relatively unchanged in animals given 1.0 and 1.5 mg/kg of MPTP, but were significantly reduced after 2.0 mg/kg of MPTP. All animals injected with a single dose of MPTP showed no overt signs of parkinsonism. In contrast, DA and metabolite concentrations in the substantia nigra were significantly reduced for all MPTP-treated animals. Reduction of dopaminergic indices in the substantia nigra did not parallel reductions in the striatum, indicating differential sensitivity of the nigrostriatal pathway to the neurotoxic effects of MPTP. The percent change in FDOPA uptake (Ki) and decarboyxlation (k3) after MPTP showed significant positive correlations to striatal DA levels, but not to the number of dopaminergic neurons. This suggests that FDOPA is a good index of striatal DA levels.

Positron emission tomography of dopamine pathways in familial Parkinsonian syndromes

Positron emission tomography (PET) scan is considered to be the most useful tool with which to assess the integrity of nigrostriatal function in the living brain. Recently, different genetic defects have been associated with a variety of familial parkinsonian syndromes, the clinical phenotypes of which have varying degrees of similarities to idiopathic parkinsonism (IP), (sporadic Parkinson's disease). This review summarizes: (1) the PET scan findings (fluorodopa uptake and raclopride binding) in both familial parkinsonian syndromes and IP; and (2) the similarities and differences of the clinical and PET features between familial parkinsonian syndromes and IP. This analysis demonstrates that more similarities than differences exist in PET scan findings in the different familial parkinsonian syndromes with the exception of pallido-ponto-nigral degeneration (PPND), that is perhaps best considered as multisystem degeneration. As a result of this analysis, we believe that while different genetic defects may underlie different mechanisms of nigrostriatal degeneration, the final pattern of nigrostriatal dysfunction is essentially similar to that of IP. 'Parkinson's disease', therefore, may not represent a single disease entity, but rather the final manifestation of different pathogenetic mechanisms-mediated by genetic or environmental factors, or an interaction of genetic and environmental factors.

Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17): PPND family. A longitudinal videotape demonstration

Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), characterized by an autosomal dominant inheritance pattern, has recently been recognized as a distinct entity that can display a confusingly broad clinical phenotype. The pallido-ponto-nigral degeneration (PPND) variant is the prototypical example of the parkinsonism-predominant pattern of FTDP-17. A longitudinal videotape demonstration of the clinical progression of this entity in a single individual, along with brief videotape segments from three additional affected individuals, is presented in order to facilitate recognition of this disorder.

Tau and transgenic animal models

Advances in genetics and transgenic approaches have a continuous impact on our understanding of Alzheimer's disease (AD) and related disorders, especially as aspects of the histopathology and neurodegeneration can be reproduced in animal models. AD is characterized by extracellular Abeta peptide-containing plaques and neurofibrillary aggregates of hyperphosphorylated isoforms of microtubule-associated protein tau. A causal link between Abeta production, neurodegeneration and dementia has been established with the identification of familial forms of AD which are linked to mutations in the amyloid precursor protein APP, from which the Abeta peptide is derived by proteolysis. No mutations have been identified in the tau gene in AD until today. Tau filament formation, in the absence of Abeta production, is also a feature of several additional neurodegenerative diseases including progressive supranuclear palsy, corticobasal degeneration, Pick's disease, and frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). The identification of mutations in the tau gene which are linked to FTDP-17 established that dysfunction of tau can, as well as Abeta formation, lead to neurodegeneration and dementia. In this review, newly recognized cellular functions of tau, and the neuropathology and clinical syndrome of FTDP-17 will be presented, as well as recent advances that have been achieved in studies of transgenic mice expressing tau and AD-related kinases and phosphatases. These models link neurofibrillary lesion formation to neuronal loss, provide an in vivo model in which therapies can be assessed, and may contribute to determine the relationship between Abeta production and tau pathology.

Positron emission tomography in pallido-ponto-nigral degeneration (PPND) family (frontotemporal dementia with parkinsonism linked to chromosome 17 and point mutation in tau gene)

Pallido-ponto-nigral degeneration (PPND) is a rapidly progressive disorder characterized by frontotemporal dementia with parkinsonism unresponsive to levodopa therapy. In this study, we have further characterized the regional abnormalities of cerebral function using PET with 6-[18F]fluoro-L-dopa (FD), [11C] raclopride (RAC), and 2-deoxy-2-fluoro-[18F]-D-glucose (FDG). FD and RAC scans were performed in 3 patients-2 new patients and a previously reported asymptomatic at-risk individual who became symptomatic 2years after the first FD scan. Cerebral glucose metabolism was studied by FDG in 2 other patients. In keeping with previous reports, there was a severe reduction of FD uptake, which affected both caudate and putamen to a similar degree in all 3 patients. RAC scans showed normal to elevated striatal D2-receptor binding in all patients. Cerebral glucose metabolism was globally reduced (>2 SD below control mean) in one patient, with maximal involvement of frontal regions, and to a lesser degree in the other patient. Our study showed severe presynaptic dopaminergic dysfunction with intact striatal D2 receptors in PPND patients, implying that the dopa unresponsiveness is probably a result of pathology downstream to the striatum. The pattern of presynaptic dysfunction contrasts with that seen in idiopathic parkinsonism, where the putamen is affected more than the caudate nucleus. The pattern of glucose hypometabolism correlates well with the presence of frontotemporal dementia.

Interest in genetic testing in pallido-ponto-nigral degeneration (PPND): a family with frontotemporal dementia with Parkinsonism linked to chromosome 17

The specific mutation on the tau gene responsible for a neurodegenerative disease known as pallido-ponto-nigral degeneration (PPND) was recently located. PPND family members are at risk for an autosomal dominant form of frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17). This study investigated whether individuals in this family would consider presymptomatic genetic testing. Surveys were sent to 66 at-risk individuals in the family; replies were received from 20 (30%). Family members were asked if they would consider having testing now or in the future, and to indicate their reasons for and against proceeding with testing. Fifty per cent (n=10) of those who were at risk and who responded indicated they would consider testing now, and 55% (n=11) would think about it in the future. The most frequently cited reasons to proceed with testing were to 'collaborate with research' (70%) and to 'know if my children are at risk' (45%). The most frequently cited reason not to pursue testing was 'I can enjoy my life more fully by not knowing' (50%). Results suggest that interest in determining whether they will manifest PPND is generally low among at-risk members of this family, despite wide support and participation in other research studies.

Morphological substrates of mental dysfunction in Lewy body disease: an update

Mental dysfunction including cognitive, behavioural changes, mood disorders, and psychosis are increasingly recognized in patients with Parkinson's disease (PD) and related disorders. Their morphological correlates are complex due to multiple system degeneration. CNS changes contributing to cognitive changes in PD include 1. Dysfunction of subcorticocortical networks with neuron losses in a) the dopaminergic nigrostriatal loop, causing striato-(pre)frontal deafferentation and mesocortico-limbic system (medial substantia nigra, ventral tegmentum); b) noradrenergic (locus coeruleus), and serotonergic systems (dorsal raphe nuclei), c) cholinergic forebrain system (nucleus basalis of Meynert, etc), and d) specific nuclei of amygdala and limbic system (thalamic nuclei, hippocampus); 2. Limbic and/or cortical Lewy body and Alzheimer type pathologies with loss of neurons and synapses, 3. Combination of subcortical, cortical, and other pathologies. In general, degeneration of subcortical and striato-frontal networks causes cognitive, executive, behavioural, and mood disorders but less severe dementia than cortical changes which, when present in sufficient numbers, are important factors for overt dementia. In PD, cortical tau pathology with similar or differential patterns than in Alzheimer disease (AD) shows significant linear correlation with cognitive decline. In dementia with Lewy bodies (DLB), the second most frequent cause of dementia in the elderly, cortical Lewy bodies (LB) may or may not be associated with amyloid plaques and neuritic AD lesions. They predominantly affect the limbic system with less frequent isocortical Braak stages, whereas the cholinergic forebrain system is more severely affected than in AD. Both neuritic degeneration in limbic system in PD and DLB and the density of cortical synapse markers correlate with neuritic AD pathology and less with cortical LB counts. Apolipoprotein E epsilon4 allele frequency may represent a common genetic background for both AD and LB pathologies but there are different proportions of plaques between DLB (less Abeta1-40) and AD (more frequent Abeta1-40). Familial parkinsonism with dementia, linked to chromosome 17 (frontotemporal dementia with Parkinsonism (FTDP-17), and other tauopathies pathologically resembling PD plus AD, are often related to mutations of the tau gene, whereas familial PD with alpha-synuclein and Parkin mutations usually show no cognitive impairment. Mood disorders, in particular depression, and psychotic complications in both PD and DLB are related to complex involvement of noradrenergic and serotonergic systems, not confirmed in AD with depression, and both the prefrontal and limbic dopaminergic systems. The specific contributions of cortical and subcortical pathologies to mental dysfunction in PD and related disorders, their relationship to AD, and their genetic and aetiological backgrounds await further elucidation.

Autosomal-dominantly inherited forms of Parkinson's disease

Today, a genetic contribution to the etiology of Parkinson's disease (PD) is generally accepted, based on the demonstration of a familial aggregation of the disease, as demonstrated by several case-control and twin-studies. However, most cases of PD appear to be sporadic, and in the majority of those with a positive family history, no clear mendelian mode of inheritance can be established. Therefore, a polygenic mode of inheritance or a multifactorial etiology is likely in these cases. On the other hand, a number of families have been identified, in whom parkinsonism is inherited as an apparently monogenic mendelian trait with high penetrance. In several of these families, the disease genes have been mapped and mutations have been identified in some of them. The first gene locus has been mapped to the long arm of chromosome 4 in a small number of families with autosomal-dominant inheritance and typical Lewy-body pathology (PARK 1), and mutations have been identified in the gene for alpha-synuclein in these kindreds. Two other loci in families with dominant inheritance have been mapped, to chromosome 2p13 (PARK 3) and to chromosome 4p, respectively. A gene causing autosomal recessive parkinsonism of juvenile onset has been mapped to chromosome 6 (PARK 2), and the causative gene has been identified and named parkin. Each of these genetically defined familial disorders share clinical characteristics that fulfill the criteria accepted for idiopathic Parkinson's disease but, as in sporadic PD, also show a variability of clinical expressions, both within and between families. At present, there is no direct evidence that any of these genes for familial Parkinsonian syndromes have a direct role in the etiology of the common sporadic form of PD. However, the elucidation of the molecular sequence of events leading to nigral degeneration in these inherited cases is likely to shed light also on the molecular pathogenesis of the common sporadic form of this disorder.

FTDP-17: an early-onset phenotype with parkinsonism and epileptic seizures caused by a novel mutation

Recently, mutations in the tau gene on chromosome 17 were found causative for autosomal dominantly inherited frontotemporal dementia and parkinsonism (FTDP-17). We describe a family carrying a missense mutation at nucleotide 1137 C --> T, resulting in the amino acid substitution P301S. Methods of investigations include clinical, electrophysiological, and imaging techniques. This kindred presents with a novel phenotype characterized by an early onset of rapidly progressive frontotemporal dementia and parkinsonism in combination with epileptic seizures. We define the dopaminergic deficits as being predominantly presynaptic by the use of single-photon emission computed tomography with a dopamine transporter ligand. The association of this early-onset phenotype with P301S mutation is not entirely consistent with current criteria for the diagnosis of frontotemporal dementias and may encourage the search for tau mutations in diseases similar but not identical to FTDP-17. Also, the change from proline to serine suggests that this mutation might contribute to tau hyperphosphorylation.

Phenotypic variation in hereditary frontotemporal dementia with tau mutations

Several mutations in the tau gene have been found in families with hereditary frontotemporal dementia and parkinsonism linked to chromosome 17q21-22 (FTDP-17). This study is the first attempt to correlate genotype and phenotype in six families with FTDP-17 with mutations in the tau gene (deltaK280, G272V, P301L, and R406W). We have investigated tau pathology in 1 P301L and 1 R406W patient. The R406W family showed a significantly higher age at onset (59.2 +/- 5.5 years) and longer duration of illness (12.7 +/- 1.5 years) than the families with the other mutations. The six families showed considerable variation in clinical presentation, but none of them had early parkinsonism. Mutism developed significantly later in the R406W family than in the other families. Frontotemporal atrophy on neuroimaging in the R406W family was less severe than in the P301L and deltaK280 families. The P301L brain contained many pretangles in the frontal and temporal cortex, and the dentate gyrus of hippocampus, showing three tau bands (64, 68, and 72 kd) of extracted tau from the frontal cortex. The presence of many neurofibrillary tangles, many diffuse and classic neuritic plaques in the temporal and parietal cortex, and the hippocampus of the same P301L brain correlated with the presence of four sarkosyl-insoluble (60, 64, 68, and 72 kd) tau bands. The coexistence of characteristic P301L and Alzheimer pathology in the same brain needs further explanation. The R406W brain showed abundant neurofibrillary tangles in several brain regions, and four tau bands (60, 64, 68, and 72 kd) of extracted tau from these regions. The slower progression of the disease in the R406W family might be explained by the microtubule-binding properties of the mutant protein.

Gene therapy in a rodent model of Parkinson's disease using differentiated C6 cells expressing a GFAP-tyrosine hydroxylase transgene

Cells expressing a tyrosine hydroxylase (TH) cDNA under control of the promoter of the human glial fibrillary acidic protein (GFAP) gene were tested for therapeutic efficacy in a rat model of Parkinson's disease. The GFAP gene encodes an intermediate filament protein found almost exclusively in astrocytes. Its promoter is of interest for gene therapy as it is expressed in astrocytes throughout postnatal life and is upregulated in response to almost any damage to the central nervous system, including Parkinson's disease. We previously showed that a line of C6 rat glioma cells that expresses a GFAP-TH transgene, C6-THA, displays increased transgene activity when differentiated by forskolin treatment. Accordingly, the effects were investigated of implantation of both undifferentiated and differentiated C6-THA cells into the striatum of rats that had been lesioned with 6-hydroxydopamine. Implantation of either cell type produced significant behavioral recovery one week after transplantation, as judged by the turning response to apomorphine. At two and three weeks after transplantation, the behavioral effect of the undifferentiated cells was no longer statistically significant, whereas that for the forskolin-differentiated cells remained robust. Transgenic TH mRNA and protein could be detected in implants of both cell types, and in agreement with the behavioral results, levels were higher for the differentiated C6-THA cells than for the undifferentiated cells. These results indicate that the GFAP promoter is sufficiently active to enable production of therapeutic levels of dopamine from a GFAP-TH transgene, and suggest the use of astrocytes for gene therapy for Parkinson's disease. They also show that beneficial modifications of cells produced by treatment while in culture may be maintained following implantation.

From genotype to phenotype: a clinical pathological, and biochemical investigation of frontotemporal dementia and parkinsonism (FTDP-17) caused by the P301L tau mutation

Frontotemporal dementia is a heterogeneous, often inherited disorder that typically presents with the insidious onset of behavioral and personality changes. Two genetic loci have been identified and mutations in tau have been causally implicated in a subset of families linked to one of these loci on chromosome 17q21-22. In this study, linkage analysis was performed in a large pedigree, the MN family, suggesting chromosome 17q21-22 linkage. Mutational analysis of the tau coding region identified a C-to-T change in exon 10 that resulted in the conversion of proline to a leucine (P301L) that segregated with frontotemporal dementia in this family. The clinical and pathological findings in the MN family emphasize the significant overlap between Pick's disease, corticobasal degeneration, and frontotemporal dementia and challenge some of the current dogma surrounding this condition. Pathological studies of two brains from affected members of Family MN obtained at autopsy demonstrate numerous tau-positive inclusions that were most prominent in the frontal lobes, anterior temporal lobes, and brainstem structures, as well as Pick-like bodies and associated granulovacuolar degeneration. These Pick-like bodies were observed in 1 patient with motor neuron disease. Because exon 10 is present only in tau mRNA coding for a protein with four microtubule binding repeats (4R), this mutation should selectively affect 4Rtau isoforms. Indeed, immunoblotting demonstrated that insoluble 4Rtau is selectively aggregated in both gray and white matter of affected individuals. Although there was significant pathological similarity between the 2 cases, the pattern of degenerative changes and tau-positive inclusions was not identical, suggesting that other genetic or epigenetic factors can significantly modify the regional topology of neurodegeneration in this condition.

A clinical pathological comparison of three families with frontotemporal dementia and identical mutations in the tau gene (P301L)

We investigated three separate families (designated D, F and G) with frontotemporal dementia that have the same molecular mutation in exon 10 of the tau gene (P301L). The families share many clinical characteristics, including behavioural aberrations, defective executive functions, language deficits, relatively preserved constructional abilities and frontotemporal atrophy on imaging studies. However, Family D has an earlier mean age of onset and shorter duration of disease than Families F and G (49.0 and 5.1 years versus 61-64 and 7.3-8.0 years, respectively). Two members of Families D and F had neuropathological studies demonstrating lobar atrophy, but the brain from Family D had prominent and diffuse circular, intraneuronal, neurofibrillary tangles not seen in Family F. The brain from Family F had ballooned neurons typical of Pick's disease type B not found in Family D. A second autopsy from Family D showed neurofibrillary tangles in the brainstem with a distribution similar to that found in progressive supranuclear palsy. These three families demonstrate that a missense mutation in the exon 10 microtubule-binding domain of the tau protein gene can produce severe behavioural abnormalities with frontotemporal lobar atrophy and microscopic tau pathology. However, the findings in these families also emphasize that additional unidentified environmental and/or genetic factors must be producing important phenotypic variability on the background of an identical mutation. Apolipoprotein E genotype does not appear to be such a factor influencing age of onset in this disease.

Genetics of Parkinson's disease

Here we review familial Parkinson's disease from clinical, as well as molecular genetic aspects. To date, two genes responsible for familial Parkinson's disease have been identified: one is the alpha-synuclein gene located in the long arm of chromosome 4, and the other is the parkin gene located in the long arm of chromosome 6. The mode of inheritance of the former is autosomal dominant and clinical features consist of levodopa-responsive parkinsonism; the age of onset is younger than that of the sporadic cases (in their 40s), and the progression is faster (average disease duration approximately nine years). The latter form is transmitted as an autosomal recessive, and clinical features consist of early onset (in their 20s), levodopa-responsive parkinsonism, and a slow progression of the disease. In addition, the tau gene has been shown to be the disease gene for familial frontotemporal dementia and parkinsonism linked to chromosome 17. There are many other clinical phenotypes of familial Parkinson's disease among which three forms have been mapped to certain chromosome loci: one is in the short arm of chromosome 2, the two other forms are in the different loci of the short arm of chromosome 4. All of them are transmitted as autosomal dominant traits manifesting levodopa responsive parkinsonism. There still exists however, other clinical phenotypes of chromosome loci which are not known. Molecular cloning of these familial Parkinson's disease genes and the elucidation of the functions of the proteins encoded will certainly contribute greatly to the investigation of the etiology and pathogenesis of more common sporadic form of Parkinson's disease.

Accelerated filament formation from tau protein with specific FTDP-17 missense mutations

Tau is the major component of the neurofibrillar tangles that are a pathological hallmark of Alzheimers' disease. The identification of missense and splicing mutations in tau associated with the inherited frontotemporal dementia and Parkinsonism linked to chromosome 17 demonstrated that tau dysfunction can cause neurodegeneration. However, the mechanism by which tau dysfunction leads to neurodegeneration remains uncertain. Here, we present evidence that frontotemporal dementia and Parkinsonism linked to chromosome 17 missense mutations, P301L, V337M and R406W, cause an accelerated aggregation of tau into filaments. These results suggest one mechanism by which these mutations can cause neurodegeneration and frontotemporal dementia and Parkinsonism linked to chromosome 17.

Frontotemporal dementia genetics

Frontotemporal dementia (FTD) is the most common syndrome in which the focus of neurodegeneration is the frontal lobes. FTD is frequently familial. It is also often due to a susceptibility locus on chromosome 17q21-22. Some 17q21-22-linked families have mutations in the tau gene and most have microscopically visible aggregates of hyperphosphorylated tau. Demonstrating that mutations in tau can produce neurodegeneration will necessitate a reassessment of the role of tau in the pathogenesis of the many diseases in which tau biology is disrupted.

Parkinsonism: siblings share Helicobacter pylori seropositivity and facets of syndrome

OBJECTIVE

Given a history of peptic ulcer is more frequent in parkinsonism, to investigate the role of Helicobacter pylori in its pathogenesis and of cross-infection in familial aggregation.

METHODS

Facets of parkinsonism were quantified in 33 elderly subjects with idiopathic parkinsonism and in their 39 siblings with double the number of controls, all obeying inclusion/exclusion criteria. Specific-IgG antibody was assayed.

RESULTS

Siblings, compared with controls, had brady/hypokinesia of gait (P< or =0.002), bradykinesia of hands (P = 0.01), abnormal posture (P = 0.001), rigidity (P < 0.001) and seborrhoea/seborrhoeic dermatitis (P = 0.02). Both parkinsonians and siblings differed from controls in the odds of being H. pylori seropositive [odds ratios 3.04 (95% C.I.: 1.22, 7.63) and 2.94 (1.26, 6.86) respectively, P < 0.02], seropositivity being found in 0.70 of sufferers.

CONCLUSION

Familial transmission of chronic infection plus part of syndrome links Helicobacter with causality. Seropositivity not being universal throughout parkinsonism, consequent on gastric atrophy +/- sporadic antibiotic exposure, might explain less aggressive disease in older sufferers.

Pathogenic implications of mutations in the tau gene in pallido-ponto-nigral degeneration and related neurodegenerative disorders linked to chromosome 17

Pallido-ponto-nigral degeneration (PPND) is one of the most well characterized familial neurodegenerative disorders linked to chromosome 17q21-22. These hereditary disorders are known collectively as frontotemporal dementia (FTD) and parkinsonism linked to chromosome 17 (FTDP-17). Although the clinical features and associated regional variations in the neuronal loss observed in different FTDP-17 kindreds are diverse, the diagnostic lesions of FTDP-17 brains are tau-rich filaments in the cytoplasm of specific subpopulations of neurons and glial cells. The microtubule associated protein (tau) gene is located on chromosome 17q21-22. For these reasons, we investigated the possibility that PPND and other FTDP-17 syndromes might be caused by mutations in the tau gene. Two missense mutations in exon 10 of the tau gene that segregate with disease, Asn279(Lys) in the PPND kindred and Pro301(Leu) in four other FTDP-17 kindreds, were found. A third mutation was found in the intron adjacent to the 3' splice site of exon 10 in patients from another FTDP-17 family. Transcripts that contain exon 10 encode tau isoforms with four microtubule (MT)-binding repeats (4Rtau) as opposed to tau isoforms with three MT-binding repeats (3Rtau). The insoluble tau aggregates isolated from brains of patients with each mutation were analyzed by immunoblotting using tau-specific antibodies. For each of three mutations, abnormal tau with an apparent Mr of 64 and 69 was observed. The dephosphorylated material comigrated with tau isoforms containing exon 10 having four MT-binding repeats but not with 3Rtau. Thus, the brains of patients with both the missense mutations and the splice junction mutation contain aggregates of insoluble 4Rtau in filamentous inclusions, which may lead to neurodegeneration.

Segregation of a missense mutation in the microtubule-associated protein tau gene with familial frontotemporal dementia and parkinsonism

Frontotemporal dementia and parkinsonism (FTDP) is the second most common cause of neurodegenerative dementia after Alzheimer's disease. Recently, several kindreds with an autosomal dominant form of FTDP have been reported and in some families the pathological locus was mapped to a 2 cM interval on 17q21-22. The MAPT gene, located on 17q21 and coding for the human microtubule-associated protein tau, is a strong candidate gene, since tau-positive neuronal inclusions have been observed in brains from some FTDP patients. Direct sequencing of the MAPT exonic sequences in 21 French FTDP families revealed in six index cases the same missense mutation in exon 10 resulting in a Pro-->Leu change at amino acid 301. Co-segregation of this mutation with the disease was demonstrated by restriction fragment analysis in two families for which several affected relatives were available. The Pro301Leu mutation was not observed in either 50 unrelated French controls or in 11 patients with sporadic frontotemporal dementia. This mutation, which occurs in the second microtubule-binding domain of the MAPT protein, is likely to have a drastic functional consequence. The observation of this mutation in several FTDP families might suggest that disruption of binding of MAPT protein to the microtubule is a key event in the pathogenesis of FTDP.

Genetics of Parkinson's disease

A genetic contribution to the etiology of Parkinson's disease (PD) is now well established, based on the demonstration of a familial aggregation of the disease as demonstrated by several case control and twin studies, and on the description of large multigenerational families, in whom PD is inherited in a Mendelian fashion. In a few families with autosomal dominant inheritance and typical Lewy-body pathology, a gene locus has been mapped to the long arm of chromosome 4, and mutations have been identified in the gene for alpha-synuclein. A gene causing autosomal recessive parkinsonism of juvenile onset has been mapped to chromosome 6, and the causative gene has been identified and named Parkin. This form of parkinsonism differs pathologically from the sporadic disease, as no Lewy bodies are found in the substantia nigra. A third locus, again in families with dominant inheritance, typical Lewy-body pathology and late onset, has been mapped to chromosome 2pl3. At present, there is no evidence that any of these genes for familial Parkinsonian syndromes have a direct role in the etiology of the common sporadic form of PD. However, the elucidation of the molecular sequence of events leading to nigral degeneration in these inherited cases is likely to shed light on the molecular pathogenesis of this common neurodegenerative disorder.

Clinical neurophysiologic findings in patients with rapidly progressive familial parkinsonism and dementia with pallido-ponto-nigral degeneration

OBJECTIVE

To present clinical electrophysiologic studies performed on the pallido-ponto-nigral degeneration (PPND) family linked to chromosome 17q21-22.

METHODS

Nine patients from this kindred were studied with 11 electroencephalograms (EEGs), 4 electroencephalographic background frequency analysis (BFA) studies, 4 electromyographic recordings (EMGs) including nerve conduction studies (NCSs), 4 electromyographic multichannel surface recordings (MSRs), one pattern visual evoked potential (VEP) study and one median nerve somatosensory evoked potential (SEP) study.

RESULTS

EEGs revealed normal findings early in the disease and diffuse slowing which became more prominent with disease progression. BFA studies demonstrated rapid decrease in mean parietal frequencies with disease progression. EMGs and NCSs showed no abnormalities. MSRs revealed action myoclonus and a dystonic process. Long loop reflexes were absent in resting hand muscles. VEPs and SEPs were normal.

CONCLUSIONS

Clinical neurophysiologic studies were consistent with a cortical and subcortical degenerative process. With clinical deterioration, there is a progressive decline in the mean parietal frequency and background rhythms. Tremor studies were consistent with action myoclonus and a dystonic process and did not show parkinsonian features of resting tremor or agonist-antagonist cocontraction. There was no evidence of peripheral nerve involvement or slowing in central sensory pathways. Electrophysiologic findings are characteristic for this illness.

Compartmental analysis of dopa decarboxylation in living brain from dynamic positron emission tomograms

The trapping of decarboxylation products of radiolabelled dopa analogs in living human brain occurs as a function of the activity of dopa decarboxylase. This enzyme is now understood to regulate, with tyrosine hydroxylase, cerebral dopamine synthesis. Influx into brain of dopa decarboxylase substrates such as 6-[18F]fluorodopa and beta-[11C]dopa measured by positron emission tomography can be analyzed by solution of linear differential equations, assuming irreversible trapping of the decarboxylated products in brain. The isolation of specific physiological steps in the pathway for catecholamine synthesis requires compartmental modelling of the observed dynamic time-activity curves in plasma and in brain. The several approaches to the compartmental modelling of the kinetics of labelled substrates of dopa decarboxylase are now systematically and critically reviewed. Labelled catechols are extensively metabolized by hepatic catechol-O-methyltransferase yielding brain-penetrating metabolites. The assumption of a fixed blood-brain permeability ratio for O-methyl-6-[18F]fluorodopa or O-methyl-beta-[11C]dopa to the parent compounds eliminates several parameters from compartmental models. However, catechol-O-methyltransferase activity within brain remains a possible factor in underestimation of cerebral dopa decarboxylase activity. The O-methylation of labelled catechols is blocked with specific enzyme inhibitors, but dopa decarboxylase substrates derived from m-tyrosine may supplant the catechol tracers. The elimination from brain of decarboxylated tracer metabolites can be neglected without great prejudice to the estimation of dopa decarboxylase activity when tracer circulation is less than 60 minutes. However, elimination of dopamine metabolites from brain occurs at a rate close to that observed previously for metabolites of glucose labelled in the 6-position. This phenomenon can cause systematic underestimation of the rate of dopa decarboxylation in brain. The spillover of radioactivity due to the limited spatial resolution of tomographs also results in underestimation of dopa decarboxylase activity, but correction for partial volume effects is now possible. Estimates of dopa decarboxylase activity in human brain are increased several-fold by this correction. Abnormally low influx of dopa decarboxylase tracers in the basal ganglia is characteristic of Parkinson's disease and other movement disorders. Consistent with postmortem results, the impaired retention of labelled dopa is more pronounced in the putamen than in the caudate nucleus of patients with Parkinson's disease; this heterogeneity persists after correction for spillover. Current in vivo assays of dopa decarboxylase activity fail to discriminate clinically distinct stages in the progression of Parkinson's disease and are, by themselves, insufficient for differential diagnosis of Parkinson's disease and other subcortical movement disorders. However, potential new avenues for therapeutics can be tested by quantifying the rate of metabolism of exogenous dopa in living human brain.

Dementia of frontal type and dementias with subcortical gliosis

The group of Frontotemporal dementias (FTD) is composed of non-Alzheimer forms of dementia characterized clinically by behavioural and personality change leading to apathy and mutism. The disorder is associated with a progressive atrophy of the frontal, anterior temporal and anterior parietal lobes of the brain with several types of underlying pathology. One type (frontal lobe degeneration) is characterized by a microvacuolar degeneration of the outer cortical laminae along with a mild and mainly subpial gliosis and a loss of nerve cells, mostly from layers II and III. Another type shows transcortical tissue cavitation and florid gliosis with neuronal degeneration characterized by the presence of tau and ubiquitin positive inclusion bodies and alpha beta-crystallin-positive ballooned neurones: such changes have been termed 'Pick-type histology', and form the basis for the modern definition of 'Pick's disease'. The aetiological relationship between these two histological types is presently unknown. Both histologies can be differently distributed topographically throughout the brain to produce syndromes of progressive language disorder, when affecting bitemporal lobes or the left hemisphere preferentially, or progressive apraxia when parietal and motor regions are involved. Either pathology can be combined with or overlaps with that of classical motor neurone disease to produce motor neurone disease dementia. The underlying cause of FTD is unknown but genetic factors are strongly implicated. About half of cases show a previous family history of a similar disorder. In several families bearing a FTD clinical and pathological phenotype, linkage to chromosome 17 has been established but the pathology of this group appears distinctive and its relation to other forms of FTD awaits further elucidation. It is still possible that the many clinical and pathological variants of FTD may reflect different phenotypic expressions of a particular genetic change(s) at a single locus on this chromosome.

Frontotemporal dementia and Parkinsonism linked to chromosome 17: a new group of tauopathies

Frontotemporal dementia is a neurological disorder characterised by personality changes, deterioration of memory and executive functions as well as stereotypical behaviour. Sometimes a Parkinsonian syndrome is prominent. Several cases of frontotemporal dementia are hereditary and recently families have been identified where the disease is linked to chromosome 17q21-22. Although, there is clinical and neuropathological variability among and within families, they all consistently present a symptomathology that has led investigators to name the disease "Frontotemporal Dementia and Parkinsonism linked to chromosome 17." Neuropathologically, these patients present with atrophy of frontal and temporal cortex as well as of basal ganglia and substantia nigra. In the majority of cases these features are accompanied by neuronal loss, gliosis and microtubule-associated protein tau deposits which can be present in both neurones and glial cells. The distribution, structural and biochemical characteristics of the tau deposits differentiate them from those present in Alzheimer's disease, corticobasal degeneration, progressive supranuclear palsy and Pick's disease. No beta-amyloid deposits are present. The clinical and neuropathological features of the disease in these families suggest that Frontotemporal Dementia and Parkinsonism linked to chromosome 17 is a distinct disorder. The presence of abundant tau deposits in the majority of these families define this disorder as a new tauopathy.

Olfactory dysfunction in familial parkinsonism

Impaired olfactory function is commonly observed in idiopathic Parkinson's disease (IPD). However, it is unknown whether it is also found in familial parkinsonism. To address this issue we administered a smell test to 12 affected, three monosymptomatic, and 12 at-risk individuals from six large parkinsonian kindreds. Three kindreds exhibited an IPD phenotype and three exhibited a parkinsonism-plus syndrome (PPS) phenotype. All but one of the affected individuals had impaired olfactory function. In contrast, only five of the 12 at-risk individuals had impaired olfactory function. The degree of olfactory impairment in the at-risk individuals was less severe than in the affected individuals. The difference in the degree of olfactory impairment in individuals exhibiting the IPD and the PPS phenotypes was not statistically significant. These findings suggest that olfactory dysfunction is a phenotypic characteristic of familial parkinsonism and that it is independent of the kindred phenotype. The appearance of olfactory dysfunction soon after disease onset raises the possibility that it is part of the neurodegenerative disease process.