蓝藻菌/β-N-甲氨基-L-丙氨酸学说在肌萎缩侧索硬化症及其他神经变性病致病机制中的研究进展

肌萎缩侧索硬化症（ALS）是一种进行性致死性神经变性病,按发病类型分为散发性和遗传性两种。其中,散发性ALS发病率全球相对一致,但在关岛等少数西太平洋地区的人群聚居地发病率有增高现象,且常伴有肌萎缩侧索硬化-帕金森-痴呆叠加症（ALS/PDC）。研究发现寄生在苏铁根部的蓝藻菌产生的非蛋白质氨基酸[β-N-甲氨基-L-丙氨酸（BMAA）]与关岛的ALS/PDC发病有关。易感个体长期暴露在富含BMAA的环境中可导致BMAA在神经蛋白中聚集,产生ALS等迟发性进行性神经变性病。本文就蓝藻菌/BMAA作为神经变性病环境致病毒素的假说及其研究进展综述如下。     

The nature of the parkinsonism-dementia complex and amyotrophic lateral sclerosis of Guam and magnesium deficiency

The parkinsonism-dementia complex (PDC) and amyotrophic lateral sclerosis (ALS) were the fatal neurological diseases, showing very high incidence during 1950-1970 and dramatic decrease after 1970 on Guam. Through the research, the present author insisted that; (1) NFTs in Guam ALS patients are merely a background feature widely dispersed in the population, (2) Guam ALS and PDC are basically different diseases, and (3) Guam ALS occurs initially as classic ALS. As pathogeneses of the diseases, intake of low calcium (Ca) and magnesium (Mg) and high aluminum water and of some plant excitatory neurotoxin has been speculated. To elucidate the pathogenesis, the author performed an experiment exposing rats to low Ca and/or Mg intake for two generations, so as to follow the actual way of human living on the island, since several generations live continuously in the same environment. The study indicates that continuous low Mg intake for two generations induces exclusive loss of dopaminergic neurons in in rats, and may support the Mg hypothesis in the pathogenesis of PDC of Guam.     

Lessons from Guam ALS/PDC study]

An extraordinarily high incidence of amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia complex (PDC) affecting the native population was discovered on the island of Guam a half century ago. Guam ALS is identical to classic ALS clinically and pathologically while PDC is marked by progressive parkinsonism and dementia. The unusual histological finding in these fetal neurodegenerative diseases is the presence of numerous neurofibrillary tangles in a selective topographic distribution unassociated with senile plaques. There have been remarkable advances in field of age-associated neurodegenerative disease after our initial study of Guam cases. Four noteworthy topics are presented in this communication. 1) Clinically, the coexistence of parkinsonism and dementia was frequently recognized in Parkinson disease and Alzheimer disease. Some other new disease entities characterized by coexistence of parkinsonism and dementia have been reported. These include progressive supranuclear palsy, frontotemporal dementia and parkinsonism linked to chromosome 17. 2) Neuropathologically, abundant neurofibrillary tangles unassociated with senile plaques were demonstrated in many diseases such as aftermath of boxing and tangle-only dementia. Furthermore, tau-positive structures were recognized not only in neurons but in glial cells in certain diseases. Tauopathy is one of the current hot research subjects. 3) Familial aggregation of Guam ALS patients provoked investigation of familial ALS elsewhere. Familial motor neuron disease with SOD1 mutation is the target of worldwide intense investigation at the present time. SOD1 gene mutation is, however, not found in Guam ALS. 4) The most striking findings of the Guam study is the gradual decline in the incidence of ALS on Guam during a quarter century and virtual disappearance of new patients. This may be linked to a remarkable change in environment and life style of the Chamorro population. The etiology of ALS is still unknown and no new treatment is available. Guam ALS/PDC is certainly one of the most mysterious riddles among age-associated neurodegenerative diseases during the last half a century.     

Muro disease or ALS-parkinsonism-dementia complex of the Kii peninsula of Japan]

"Muro disease" is an endemic ALS in the Muro district that includes the southern coastal mountainous areas of the Kii peninsula of Japan. Epidemiological survey in 1960s disclosed extremely high incidence of ALS in two villages, Hohara and Kozagawa, and disappearance of high incidence by early 1980s was reported with its etiology unsolved. We resurveyed for neurodegenerative diseases in Hohara and found continuous high ALS incidence. We also found parkinsonism-dementia complex (PDC) verified neuropathologically. ALS and PDC frequently occurred in one individual simultaneously and affected many members in the same family, and neuropathological findings of ALS and PDC were similar to each other, showing a combination of upper and lower motor neuron involvements and many neurofibrillar tangles (NFTs) in the brainstem and cerebral cortex, resembling those of ALS/PDC on Guam. TDP-43 positive inclusions were found in the dentate gyrus of the hippocampus and spinal motor neurons in all cases examined. Age-adjusted incidence rates during 1950 and 2000 have showed that incidence of ALS was gradually declining for 50 years while that of PDC rose up steeply in 1990s. No particular environmental factors were confirmed and gene analyses of candidate genes of ALS, parkinsonism and dementia failed to reveal any mutations. Continuing high incidence and high rates of familial occurrence suggest that primary cause of Kii ALS/PDC may be genetic rather than environmental.     

ALS-parkinsonism-dementia complex of Kii and other related diseases in Japan

The ALS/parkinsonism-dementia complex (PDC) of Kii is an endemic disease with a diverse phenotypic expression characteristic of classical ALS, parkinsonism and dementia. Its clinical and neuropathological manifestations are similar to a syndrome found in Guam, sharing classical ALS pathology together with many neurofibrillary tangles in the brain. The incidence rates of ALS declined dramatically between the 1950s and 1980s. In the 1990 s, Kuzuhara found a high incidence of PDC with abundant neurofibrillary tangles, similar to Guamanian PDC. The incidence rates of PDC dramatically rose during the 1980s and 1990 s, and PDC replaced ALS. More than 70% of patients in the endemic region had a family history of ALS or PDC. We recently found a new gene OPTN causing ALS, and have extended its clinical survey in Japan. Two autopsied cases showed involvement of basal ganglia and/or cerebral cortex with neurofibrillary tangles. A few family members also showed dementia and parkinsonism without evidence of motor neuron disease. Moreover the penetrance seems to be incomplete. Despite these similarities, OPTN mutations were not found in the Kii patients. We speculate that the Kii/ALS-PDC could primarily be a genetic disease, and its clinical manifestation is modified by other genes or environmental factors.     

Amyotrophic lateral sclerosis of Guam: the nature of the neuropathological findings

To elucidate the fundamental differences and similarities of the neuropathological features and etiopathogenesis of the amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia complex (PDC) of Guam, we conducted a topographic, quantitative and histological investigation of tau-containing neurons, neurofibrillary tangles (NFTs), Bunina bodies and ubiquitinated inclusion bodies in 27 non-ALS non-PDC Guamanian subjects, as well as 10 Guam ALS patients, 28 PDC patients, and 5 patients with combined ALS and PDC (ALS-PDC). The topographic distribution of NFTs was basically the same in each disease and also in the non-ALS non-PDC group. There were relatively few, if any, NFTs in non-ALS non-PDC subjects and ALS patients, but there were many, especially in the frontal and temporal cortex, in Guam PDC and ALS-PDC patients. The histological and ultrastructural features of Bunina bodies in Guam ALS and ALS-PDC patients were similar to those reported in classic ALS. The ratio of occurrence of the inclusion in Guam ALS and ALS-PDC patients was similar to that reported so far in classic ALS. Ubiquitinated skein-like inclusion bodies were observed in the spinal anterior horn cells in Guam ALS and ALS-PDC patients. These findings indicate that classic ALS does exist on Guam, that NFTs in Guam ALS patients are merely a background feature widely dispersed in the population, that the mechanism of neuronal degeneration of Guam ALS is basically different from that of PDC, and that Guam ALS occurs initially as classic ALS.Supported in part by a Grant-in-Aid for Scientific Research (c) 05680653 from the Ministry of Education, Science and Culture and a research grant for CNS degenerative diseases from the Ministry of Health and Welfare, JapanMedical student of Leiden University, Holland, in 1981. He stayed on Guam and accomplished his thesis on part of this study under the guidance of Drs. K.-M. Chen and K. Oyanagi.     

Beta-methylamino-alanine (BMAA) injures hippocampal neurons in vivo

The unusually high incidence of amyotrophic lateral sclerosis/Parkinson-dementia complex (ALS/PDC) among the Chamorro people of Guam has fueled an intense search for the etiologic agent responsible for this neurodegenerative disease. Recently, a biomagnification hypothesis was proposed to account for the role of dietary consumption of beta-methylamino-alanine (BMAA) in patients with ALS/PDC. However, this hypothesis is hotly debated and a direct association between BMAA and neuronal injury in vivo has been lacking. We provide evidence that introduction of BMAA into the CNS of mice leads to sporadic death of hippocampal neurons, supporting a direct causal link between BMAA and neuronal injury.     

Incidence of amyotrophic lateral sclerosis and of the parkinsonism-dementia complex of Guam, 1950-1989

Studies representing the accumulated information from the first 30 years of research effort on Guam (1950-1979) have demonstrated a varying degree of decline in the incidence of amyotrophic lateral sclerosis (ALS) and the parkinsonism-dementia complex (PDC) of Guam. Analysis with more complete information for the period 1980-1989 provides more valid estimates of the later patterns in the incidence of ALS and PDC and affords a more extensive assessment of trends over a 40-year period. The annual age-adjusted incidence of ALS was 7/100,000 and the annual age-adjusted incidence of PDC was 22/100,000 in 1989. The incidence was much higher for the period 1980-1989 than suggested in previous reports. These findings provide compelling evidence that this spectrum of neurodegenerative diseases continues to have a significant impact on the health of the Chamorro people of Guam.     

Hippocampal and entorhinal cortex neurofibrillary tangle formation in Guamanian Chamorros free of overt neurologic dysfunction

Since first described, amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) of Guam has represented an important model of age-related neurodegenerative disease. ALS/PDC is characterized neuropathologically by severe widespread involvement by neurofibrillary tangles (NFTs). Over the past 30 years there has been a dramatic decrease in the incidence of ALS and a 10-year increase in the age of onset of ALS and PDC. In 1979, Anderson et al reported evidence of significant NFT involvement in Guam natives who had been free of evidence of neurologic dysfunction. Using the slides from this study, we re-examined the extent of hippocampus and entorhinal NFT involvement and compared it to brains recently obtained from neurologically intact Guam natives and age-matched controls from New York. The tendency towards hippocampal and entorhinal NFT formation continues to be encountered among the inhabitants of Guam, particularly among those over age 50. although severe involvement was less commonly noted in relatively young individuals (< 50 years). As noted by Anderson et al, the pattern of neuropathologic lesions seen in those with extensive NFT involvement suggests that such cases represent preclinical examples of ALS/PDC in individuals who have yet to accumulate a sufficient burden of pathology to attract clinical attention and diagnostic evaluation.     

Amyotrophic lateral sclerosis and parkinsonism‐dementia complex of the Hohara focus of the Kii Peninsula: A multiple proteinopathy?

The high incidence of amyotrophic lateral sclerosis (ALS) and parkinsonism‐dementia complex (PDC) has been previously known in the Kii Peninsula of Japan and in Guam. Recently, the accumulation of various proteins, such as tau, trans‐activation response DNA binding protein 43 kDa (TDP‐43), and alpha‐synuclein (αSyn), was reported in the brains of patients with ALS/PDC in Guam. To confirm whether similar findings are present in Kii ALS/PDC, we neuropathologically examined the brains and spinal cords of 18 patients with ALS/PDC (clinical diagnoses: eight ALS and 10 PDC) in Hohara Village, which is the eastern focus of Kii ALS. The average age at death was 71.6 years, and 16 patients (88.9%) had a family history of ALS/PDC. Autopsy specimens were immunohistochemically examined with antibodies against four major proteins. Neurofibrillary tangles, including ghost tangles, and tau‐positive astrocytes were distributed widely in all of the brains examined, and TDP‐43‐positive neuronal cytoplasmic inclusions were observed mainly in the limbic system. Synuclein pathology was present in 14 patients (77.8%). These patients were classified into three pathological subtypes according to the most prominent proteinopathy: the tauopathy‐dominant type, the TDP‐43 proteinopathy‐dominant type, and the synucleinopathy‐dominant type. Five patients with severe tau deposition showed clinical features of atypical parkinsonism and dementia with or without motor neuron disease. Eight patients were predominated by phosphorylated TDP‐43 inclusions and clinically showed ALS, and five patients were predominated by synuclein pathology and clinically showed signs of PDC. Based on the common characteristic tau pathology, three subtypes seemed to be pathologically continuous on a spectrum of a single disease. Thus, we conclude that ALS/PDC in the Hohara focus of the Kii Peninsula is a single disease characterized neuropathologically by a multiple proteinopathy, even though the clinical manifestations of the three subtypes differed from each other. It remains unclear whether the coexistence of the three proteinopathies was incidental or pathogenetically related.     

Amyotrophic lateral sclerosis/parkinsonism dementia complex: transgenic mice provide insights into mechanisms underlying a common tauopathy in an ethnic minority on Guam

Intracytoplasmic filamentous tau inclusions are neuropathological hallmarks of amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) of Guam and the defining lesions of other neurodegenerative disorders known as tauopathies. Here we review current insights into the cell and molecular neuropathology of ALS/PDC, a common tauopathy in the Chamorro population on Guam. We also summarize recent advances in understanding this disorder through studies of transgenic (Tg) mouse models of this tauopathy. Briefly, overexpression of human tau isoforms in the central nervous system of Tg mice resulted in a neurodegenerative tauopathy with a phenotype similar to ALS/PDC. Specifically, argyrophilic, congophilic, and tau immunoreactive inclusions accumulated with age in cortical and brainstem neurons of these mice, but they were most abundant in spinal cord neurons, and the inclusions contained 10- to 20-nm tau-positive straight filaments. There also was extensive gliosis in spinal cord associated with axonal degeneration in the ventral roots, while remaining axons in spinal nerves showed a loss of microtubules and reduced fast axonal transport. With advancing age, these Tg mice showed increasing motor weakness, and this was accompanied by a progressive increase in the phosphorylation and insolubility of brain and spinal cord tau proteins. Thus, tau Tg mice recapitulate key phenotypic features of ALS/PDC neuropathology in an ethnic minority on Guam, and these animal models provide new opportunities to discover novel therapies for this and related tauopathies.     

Neuropathology of parkinsonism-dementia complex and amyotrophic lateral sclerosis of Guam: an update

A comparative study was performed to investigate the differences and similarities of the neuropathological findings in the parkinsonism-dementia complex (PDC) and amyotrophic lateral sclerosis (ALS) of Guam, progressive supranuclear palsy and classic ALS. Based on the findings, it is proposed that (a) PDC is a discrete disease entity, (b) NFTs in Chamorro ALS are merely a background feature widely distributed in this population, (c) Chamorro ALS is a disease combined with classic ALS and neurofibrillary degeneration, (d) thus a subtype of “Guam ALS” is not present, and (e) PDC and ALS of Guam are different diseases.

     

Clinical features and changing patterns of neurodegenerative disorders on Guam, 1997-2000.

BACKGROUND: In the 1950s, high-incidence ALS and Parkinson-dementia complex (PDC) were identified among Chamorros, the native inhabitants of Guam. Brains of patients with these syndromes showed widespread neurofibrillary tangles. Although ALS and PDC were reported to have dramatically declined in the 1980s, new cases are still encountered. Late-life dementia has received little study among Chamorros. METHODS: From 1997 to 2000, the authors evaluated newly referred and previously identified patients. They screened first-degree relatives of previous registries, and subjects aged 60 or older. Subjects who scored below a cognitive test cutoff or had symptoms or signs consistent with parkinsonism or ALS underwent psychometric testing, assessment by a neurologist, and laboratory studies as appropriate. Consensus diagnoses were made. RESULTS: The authors identified 194 Chamorros with ALS (n = 10), PD (n = 11), PDC (n = 90), or late-life dementia (n = 83). Mean ages at onset were 55 for ALS, 68 for PDC, 63 for PD, and 74 for dementia. Late-life dementia was more common in women, and met criteria for probable or possible AD. The APOE-epsilon 4 allele frequency was uniformly low regardless of neurologic diagnosis. CONCLUSIONS: The rapid decline of high-incidence ALS on Guam over the past 40 years suggests the contribution of a modifiable environmental factor. PDC remains relatively common, with an unchanged clinical picture apart from later age at onset. Dementia among elderly Chamorros (termed "Mariana dementia") resembles AD. Autopsy studies will clarify whether this dementia is related to AD pathology or represents a late-life neurofibrillary tangle syndrome more closely allied to PDC.     

Neuroepidemiologic research initiatives on Guam: past and present.

Since the middle of this century, a remarkable concentration of cases of neurodegenerative disease(s), referred to as amyotrophic lateral sclerosis and Parkinson-dementia complex (ALS/PDC), has been recognized among Chamorro natives of Guam. Intense investigations over the last 4 decades have failed to determine the etiology of these invariably fatal diseases. Over the same time period, the incidence of ALS has decreased dramatically, the incidence of PDC has decreased, but to a lesser degree, and age at onset has shifted to a later age by about 1 decade. Almost 50% of demented patients present without the classical Parkinsonian features of PDC, and the morphological picture has changed. Results of past and present research initiatives are reviewed.     

Molecular genetic analysis of amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) in the Kii peninsula

Recent clinical research have revealed that more than 70% of the patients with ALS/PDC, which is highly prevalent in Hohara area in the Kii peninsula, have family history. 80% of Guamanian patients, who have identical pathological findings to those of ALS/PDC in Kii, are also known to have family history with non-Mendelian trait. These facts suggest strong genetic predisposition to ALS/PDC in both Kii and Guam. However, no genes associated with ALS/PDC have been identified by molecular genetic studies using candidate gene approach. To identify the causative or susceptibility genes for ALS/PDC, we have conducted a genomewide linkage analysis for five families with ALS/PDC in Hohara. The fact that affected individuals were ascertained in successive generations suggest an autosomal dominant (AD) inheritance, while the presence of consanguinity suggests an autosomal recessive (AR) inheritance. Although we can raise possibilities of AD model with incomplete penetrance or AR model with high gene frequency (pseudo-dominant model), the mode of inheritance of ALS/PDC families is complicated and controversial. Therefore, we are also conducting model-free (non-parametric) linkage analysis to identify the disease locus without setting mode of inheritance. More family members and detailed clinical evaluations are required to obtain the convincing evidence of linkage.     

Clinical aspects, imaging and neuropathology of Kii ALS/PDC]

During 1996 and 2006, we examined clinically 37 patients and neuropathologically 13 autopsy cases with amyotrophic lateral sclerosis/parkinsonism-dementia complex of the Kii peninsula (Kii ALS/PDC). The ages of onset were between 52 years and 74 years (mean age: 65.3 years). The male to female ratio was 1:1.85. The ratio of positive family history where ALS or PDC occurred within the fourth degree of the relatives was 78.4% in the patients with Kii ALS/PDC. The average duration of the illness was 6.47 years. Kii ALS/PDC was divided into five clinical subtypes, pure ALS form, ALS with dementia form, PDC with parkinsonism predominant form, PDC with dementia predominant form (that is called late-life dementia in Guam) and PDC with ALS features form. Unique pigmentary retinopathy was found in 33.3% of the patients with Kii ALS/PDC. CT/MRI images showed atrophy of the frontal and temporal lobes and SPECT images showed a decrease in the blood flow of the frontal and temporal lobes. The cardiac 123I-MIBG uptake was decreased in 4 out of 8 patients with ALS/PDC and the decrease in uptake correlated with the modified Hoehn-Yahr staging. The cardinal neuropathological features of Kii ALS/PDC were abundant neurofibrillary tangles (NFTs) associated with loss of nerve cells in the cerebral cortex and the brain stem, and findings of ALS neuropathology. Ultrastructurally, NFTs consisted of paired helical filaments. Tau protein, a main component of NFTs, was consisted of 3R and 4R tau isoforms, and phosphoryrated at 18 sites of tau phosphoryrated sites. The neurons of dentate gyrus of hippocampus and anterior horn cells were stained with anti-TDP-43 antibody. The clinical and neuropathological aspects of Kii ALS/PDC are regarded as being identical with those of Guam ALS/PDC.     

ALS and PDC of Guam: forty-year follow-up

BACKGROUND: It was noticed in the mid-1950s that the incidence of ALS and parkinsonism--dementia complex (PDC) were much higher on Guam than anywhere else in the world. In 1958, a registry of patients and controls was established to ascertain the familial and genetic aspects of these diseases. Patients and individually matched controls and their relatives were registered from 1958 to 1963. The registry was updated and analyzed in 1998 through 1999. OBJECTIVE: To ascertain whether first-degree relatives of patients had a higher risk for developing ALS or PDC than relatives of controls. Methods: During the period of 1958 to 1963, 126 new patients and 126 individually matched controls and their respective first-degree relatives and spouses were evaluated neurologically and registered. Forty years later, the number of new cases among the patient and control relatives were compared to an expected number of new cases based on the age- and sex-specific incidence of ALS and PDC in the population at large. RESULTS: From 1958 to 1999, there were 102 new ALS or PDC cases among relatives of patients and 33 among relatives of controls. These values were compared with the derived expected values. There were more observed than expected new cases among patients' relatives, and less observed cases than expected among the controls' relatives. CONCLUSIONS: Relatives of patients with ALS or PDC have significantly higher risks for developing the disease than the Guamanian population, whereas relatives of controls have significantly lower risks.     

Occurrence of beta-methylamino-l-alanine (BMAA) in ALS/PDC patients from Guam

We tested the brain tissues of the Chamorro people of Guam who died of amyotrophic lateral sclerosis/Parkinsonism dimentia complex (ALS/PDC) for the neurotoxin beta-methylamino-l-alanine (BMAA). We used validated high-pressure liquid chromatography and liquid chromatography-mass spectrometry analyses to test well-characterized archival tissues of the superior frontal gyrus from eight Chamorros from Guam and a comparison group of 15 Canadians. BMAA was found as a free amino acid in 83% of Chamorro ALS/PDC patients (3-10 microg/g) as a protein-associated amino acid in 100% of the Chamorro individuals (149-1190 microg/g). Both forms of BMAA were also found at comparable levels in two Canadians who died of progressive neurodegenerative disease. BMAA, which is produced by cyanobacteria, may be associated with some cases of neurodegenerative disease.