Neurofibrillary tangles of Guamanian amyotrophic lateral sclerosis, parkinsonism-dementia and neurologically normal Guamanians contain a 4- to 4.5-kilodalton protein which is immunoreactive to anti-amyloid beta/A4-protein antibodies

Western Pacific ALS-PDC: Evidence implicating cycad genotoxins

Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex (ALS-PDC) is a disappearing neurodegenerative disorder of apparent environmental origin formerly hyperendemic among Chamorros of Guam-USA, Japanese residents of the Kii Peninsula, Honshu Island, Japan and Auyu-Jakai linguistic groups of Papua-Indonesia on the island of New Guinea. The most plausible etiology is exposure to genotoxins in seed of neurotoxic cycad plants formerly used for food and/or medicine. Primary suspicion falls on methylazoxymethanol (MAM), the aglycone of cycasin and on the non-protein amino acid β-N-methylamino-L-alanine, both of which are metabolized to formaldehyde. Human and animal studies suggest: (a) exposures occurred early in life and sometimes during late fetal brain development, (b) clinical expression of neurodegenerative disease appeared years or decades later, and (c) pathological changes in various tissues indicate the disease was not confined to the CNS. Experimental evidence points to toxic molecular mechanisms involving DNA damage, epigenetic changes, transcriptional mutagenesis, neuronal cell-cycle reactivation and perturbation of the ubiquitin-proteasome system that led to polyproteinopathy and culminated in neuronal degeneration. Lessons learned from research on ALS-PDC include: (a) familial disease may reflect common toxic exposures across generations, (b) primary disease prevention follows cessation of exposure to culpable environmental triggers; and (c) disease latency provides a prolonged period during which to intervene therapeutically. Exposure to genotoxic chemicals ("slow toxins") in the early stages of life should be considered in the search for the etiology of ALS-PDC-related neurodegenerative disorders, including sporadic forms of ALS, progressive supranuclear palsy and Alzheimer's disease.

Dysfunction of Protein Quality Control in Parkinsonism-Dementia Complex of Guam

Guam parkinsonism–dementia complex (G-PDC) is an enigmatic neurodegenerative disease that is endemic to the Pacific island of Guam. G-PDC patients are clinically characterized by progressive cognitive impairment and parkinsonism. Neuropathologically, G-PDC is characterized by abundant neurofibrillary tangles, which are composed of hyperphosphorylated tau, marked deposition of 43-kDa TAR DNA-binding protein, and neuronal loss. Although both genetic and environmental factors have been implicated, the etiology and pathogenesis of G-PDC remain unknown. Recent neuropathological studies have provided new clues about the pathomechanisms involved in G-PDC. For example, deposition of abnormal components of the protein quality control system in brains of G-PDC patients indicates a role for proteostasis imbalance in the disease. This opens up promising avenues for new research on G-PDC and could have important implications for the study of other neurodegenerative disorders.

Guam dementia syndrome revisited in 2011

PURPOSE OF REVIEW

This review covers the amyotrophic lateral sclerosis (ALS)/parkinsonism dementia complex (PDC) of Guam. Clinical and epidemiological characteristics, genetic possible and environmental causes, and neuropathological features of the disease are discussed.

RECENT FINDINGS

Recent studies of clinical syndromes and neuropathological studies are compared with previous descriptions of the disease. The latest genetic and environmental studies are also reviewed.

SUMMARY

In recent years, understanding of the molecular pathogenesis of neurodegenerative diseases has evolved. ALS/PDC shares neuropathological features found in many neurodegenerative diseases such as Alzheimer's disease, Lewy body disease, and frontotemporal lobar degeneration. Thus, examining ALS/PDC may provide further explanations on how various proteins seen in neurodegenerative disorders may be interrelated.

Enduring involvement of tau, beta-amyloid, alpha-synuclein, ubiquitin and TDP-43 pathology in the amyotrophic lateral sclerosis/parkinsonism-dementia complex of Guam (ALS/PDC)

Guam ALS/PDC is a severe tangle forming disorder endemic to Guam with features overlapping such neurodegenerative disorders as Alzheimer disease (AD), Parkinson disease (PD), progressive supranuclear palsy (PSP), ALS, corticobasal degeneration (CBD) and pallido-ponto-nigral degeneration (PPND). Since the prevalence is declining, we examined brain tissue from 35 clinically diagnosed Chamorro patients with ALS/PDC and two Chamorro controls autopsied between 1946 and 2006, to determine if distinct variations in the pathology could be identified up to this time. Although the age at autopsy increased by 4.5-5 years per decade, we identified no qualitative differences in pathological deposits with antibodies against tau, ubiquitin, A beta, alpha-synuclein and TDP-43, indicating that these more recently identified proteins have been involved in the neuropathogenesis over the past 6 decades. Tau and TDP-43 positive neuronal, oligodendroglial and astrocytic inclusions involving multiple nerve fiber tracts occurred in both the ALS and PDC types, reinforcing the concept that these forms are part of the same disorder. The results obtained may help to define the commonality of the Guam disease with other tangle forming disorders and may help in monitoring the epidemiological changes that are taking place.

Intraneuronal Abeta immunoreactivity is not a predictor of brain amyloidosis-beta or neurofibrillary degeneration

Amyloid beta (Abeta) immunoreactivity in neurons was examined in brains of 32 control subjects, 31 people with Down syndrome, and 36 patients with sporadic Alzheimer's disease to determine if intraneuronal Abeta immunoreactivity is an early manifestation of Alzheimer-type pathology leading to fibrillar plaque formation and/or neurofibrillary degeneration. The appearance of Abeta immunoreactivity in neurons in infants and stable neuron-type specific Abeta immunoreactivity in a majority of brain structures during late childhood, adulthood, and normal aging does not support this hypothesis. The absence or detection of only traces of reaction with antibodies against 4-13 aa and 8-17 aa of Abeta in neurons indicated that intraneuronal Abeta was mainly a product of alpha- and gamma-secretases (Abeta(17-40/42)). The presence of N-terminally truncated Abeta(17-40) and Abeta(17-42) in the control brains was confirmed by Western blotting and the identity of Abeta(17-40) was confirmed by mass spectrometry. The prevalence of products of alpha- and gamma -secretases in neurons and beta- and gamma-secretases in plaques argues against major contribution of Abeta-immunopositive material detected in neuronal soma to amyloid deposit in plaques. The strongest intraneuronal Abeta(17-42) immunoreactivity was observed in structures with low susceptibility to fibrillar Abeta deposition, neurofibrillary degeneration, and neuronal loss compared to areas more vulnerable to Alzheimer-type pathology. These observations indicate that the intraneuronal Abeta immunoreactivity detected in this study is not a predictor of brain amyloidosis or neurofibrillary degeneration. The constant level of Abeta immunoreactivity in structures free from neuronal pathology during essentially the entire life span suggests that intraneuronal amino-terminally truncated Abeta represents a product of normal neuronal metabolism.

Guamanian neurodegenerative disease: electrophysiologic findings

Amyotrophic lateral sclerosis (ALS), parkinsonism and/or dementia are highly prevalent among the Chamorro population of Guam. The incidence of Guamanian ALS has markedly declined in recent years, but these incidence figures may reflect underascertainment of subclinical disease. Guamanian Chamorro patients have not been systematically studied using modern clinical neurophysiological techniques. Electromyography (EMG: needle exam and nerve conduction studies) was used to study 29 patients with the major subtypes of Guamanian neurodegenerative disease, as well as 11 neurologically normal Guamanian Chamorro subjects. Central conduction was assessed by somatosensory evoked potentials (SEP's) in 16 patients. EMG evidence of peripheral neuropathy, (often subclinical) was found in 45% of Guamanian patients but no Chamorro control subjects. Diabetes mellitus, which is highly prevalent in this population, was present in some, but not all of these cases. Clinically unsuspected motor neuron disease was identified by EMG in only one of the 23 Guamanian patients with parkinsonism and/or dementia and in none of the 11 Chamorro control subjects. Two of seven patients with the clinical phenotype of Guamanian ALS had a more benign EMG pattern on the needle electrode exam with absence of fibrillation and fasciculation potentials. Three of 16 patients (all with parkinsonism and dementia) had mildly abnormal tibial SEP's. No patient had EMG evidence of myopathy or a defect of neuromuscular transmission. We conclude: (1) peripheral neuropathy may be a manifestation of Guamanian neurodegenerative disease; (2) the declining prevalence of ALS on Guam is not associated with the development of a subclinical form of motor neuron disease; (3) the substantial overlap of Guamanian ALS with parkinsonism-dementia reported in prior decades is no longer apparent; (4) abnormal central conduction, as assessed by tibial SEP's, is present in some patients with Guamanian parkinsonism-dementia.

The Guam cycad toxin methylazoxymethanol damages neuronal DNA and modulates tau mRNA expression and excitotoxicity

As in Alzheimer's disease, brains of Guam Chamorros with amyotrophic lateral sclerosis (ALS) and Parkinsonism-dementia complex (PDC) contain intraneuronal-paired helical filaments composed of accumulated phosphorylated tau protein. Tau mRNA expression in rat neuronal cultures-normally modulated by glutamate-increases after treatment with the aglycone of cycasin, a cycad-derived toxin whose concentration in Chamorro food varies with disease incidence. Elevated Tau gene expression in vitro is coincident with increased cycasin-related DNA adducts and reduced DNA repair. Cycasin and endogenous glutamate may together promote the accumulation of tau protein and neuronal degeneration in Western Pacific ALS/PDC.

Neurofibrillary tangles of Guam parkinson-dementia are associated with reactive microglia and complement proteins

Guamanian parkinsonism-dementia, locally described as bodig, is characterized by the widespread appearance of neurofibrillary tangles in cortical and subcortical areas. These tangles have similar regional distribution and immunohistochemical profile to those found in Alzheimer disease (AD). We studied the immunohistochemical staining of these tangles, as well as those of AD, using antibodies to complement proteins and related molecules. In bodig, as in AD, extracellular tangles were intensely decorated with antibodies to C1q, C4d and C3d, but not fraction Bb of factor B, properidin or immunoglobulins. This is evidence that the classical, but not the alternative complement pathway is activated on extracellular tangles and that the activation is independent of antibodies. Immunohistochemical staining for amyloid P, an in vitro activator of complement, was remarkably similar to that for the C1q, C4d and C3d in both bodig and AD. This was not the case for beta-amyloid protein (BAP), another in vitro complement activator. Positive staining was observed in only a minority of extracellular tangles in bodig and was only rarely observed in those of AD. BAP would therefore not appear to be a candidate for activating complement on extracellular neurofibrillary tangles. Reactive microglia and reactive astrocytes were closely associated with complement positive extracellular neurofibrillary tangles, indicating an inflammatory response similar to that seen in AD.

Relationship of amyloid beta/A4 protein to the neurofibrillary tangles in Guamanian parkinsonism-dementia

The Chamorro population of the island of Guam is highly susceptible to a disease called lytico-bodig (LB), which clinically resembles a mixture of amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD) and Alzheimer disease (AD). The disease is characterized by the widespread development of neurofibrillary tangles in the central nervous system. These tangles have an immunohistochemical profile indistinguishable from that seen in AD. We studied by immunohistochemistry the occurrence of intracellular and extracellular neurofibrillary tangles in LB in the entorhinal cortex, hippocampus and substantia nigra using antibodies to tau protein and ubiquitin. We also studied the relationship of these tangles to amyloid precursor protein (APP) and its beta-amyloid fragment (BAP), using multiple antibodies to BAP and other APP sequences. In advanced cases of LB, the development of neurofibrillary tangles was far more severe than in advanced cases of AD. Virtually all neurons of CA-1 and the subiculum were lost and only ghost tangles remained. In areas dominated by such extracellular tangles, BAP deposits were frequently observed developing around the fibers of ghost tangles. In some cases, the deposits covered only a few of the fibers, but in others, they seemed to envelope the complete tangle. The deposits were thioflavin S and Congo red positive, indicating that the BAP was in a consolidated form. We describe these entities as "tangle-associated amyloid deposits". Such BAP deposits have previously been described in some cases of AD, dementia pugilistica and LB. However, we found them in all cases of LB with dementia in the hippocampal-entorhinal areas and in most cases in the substantia nigra. They do not evolve from diffuse BAP deposits since they are remote from them, and they do not trap dystrophic neurites. The fact that extracellular tangle material can act as a nidus for BAP build-up in LB suggests that further consideration needs to be given to the ways in which extracellular BAP deposits are formed.

Amyotrophic lateral sclerosis and parkinsonism-dementia from Guam: differences in neurofibrillary tangle distribution and density in the hippocampal formation and neocortex

Amyotrophic lateral sclerosis/parkinsonism-dementia complex is a highly prevalent neurodegenerative disorder among the native Chamorro population of Guam, and is characterized by widespread formation of neurofibrillary tangles. In the present study, the distribution of neurofibrillary tangles was quantitatively assessed in the cerebral cortex of cases presenting with either predominant amyotrophic lateral sclerosis or parkinsonism-dementia symptomatology. Results show that although the regional and laminar lesion distribution is qualitatively similar in both groups, cases with predominant parkinsonism-dementia generally have higher lesion densities than cases with amyotrophic lateral sclerosis. Interestingly, layer II of the entorhinal cortex was affected to the same degree in both conditions. In both groups, the CA1 field of the hippocampus, subiculum, and entorhinal cortex were the most affected areas. In the neocortex, the perirhinal and inferior temporal cortex consistently had higher lesion densities than the frontal, parietal, and cingulate cortex, whereas the visual cortex was practically devoid of lesions. Also, most of the neurofibrillary tangles were located in the supragranular layers of the neocortex, with relatively low densities in the infragranular layers, in both brain groups. Interestingly, the primary motor cortex contained more neurofibrillary tangles in parkinsonism-dementia than in amyotrophic lateral sclerosis cases. It is possible that the differences in regional neurofibrillary tangle densities reflect the variable severity of the dementing process observed between the two groups of patients. Several studies on Alzheimer's disease and related disorders indicate that the regional and laminar cortical localization of neurofibrillary tangles may parallel the degeneration of specific corticocortical projections. The present data suggest that the population of corticocortical projections involved in Guamanian cases differs substantially from that affected in Alzheimer's disease. The differential distribution and densities of the lesions may contribute to the differences in symptomatology and severity of dementia among Alzheimer's disease and Guamanian cases, although these neurodegenerative disorders as well as related illnesses may share certain etiopathogenetic mechanisms.