The spectrum of disease and tau pathology of nodding syndrome in Uganda

Nodding syndrome: A role for environmental biotoxins that dysregulate MECP2 expression?

Nodding syndrome is an epileptic encephalopathy associated with neuroinflammation and tauopathy. This initially pediatric brain disease, which has some clinical overlap with Methyl-CpG-binding protein 2 (MECP2) Duplication Syndrome, has impacted certain impoverished East African communities coincident with local civil conflict and internal displacement, conditions that forced dependence on contaminated food and water. A potential role in Nodding syndrome for certain biotoxins (freshwater cyanotoxins plus/minus mycotoxins) with neuroinflammatory, excitotoxic, tauopathic, and MECP2-dysregulating properties, is considered here for the first time.

Tau filaments with the chronic traumatic encephalopathy fold in a case of vacuolar tauopathy with VCP mutation D395G

Dominantly inherited mutation D395G in the gene encoding valosin-containing protein causes vacuolar tauopathy, a type of behavioural-variant frontotemporal dementia, with marked vacuolation and abundant filamentous tau inclusions made of all six brain isoforms. Here we report that tau inclusions were concentrated in layers II/III of the frontotemporal cortex in a case of vacuolar tauopathy. By electron cryomicroscopy, tau filaments had the chronic traumatic encephalopathy (CTE) fold. Tau inclusions of vacuolar tauopathy share this cortical location and the tau fold with CTE, subacute sclerosing panencephalitis and amyotrophic lateral sclerosis/parkinsonism-dementia complex, which are believed to be environmentally induced. Vacuolar tauopathy is the first inherited disease with the CTE tau fold.

Onchocerciasis-associated epilepsy: Charting a path forward

This narrative review intends to inform neurologists and public health professionals about Onchocerciasis-Associated Epilepsy (OAE), a neglected public health problem in many remote onchocerciasis-endemic areas. For epidemiological purposes, we define OAE as sudden-onset of convulsive and non-convulsive seizure types, including head nodding seizures (nodding syndrome) in a previously healthy child aged 3 to 18 years in the absence of any other obvious cause for epilepsy, all happening within an area with high ongoing Onchocerca volvulus transmission. Several OAE pathophysiological mechanisms have been proposed, but none has been proven yet. Recent population-based studies showed that strengthening onchocerciasis elimination programs was followed by a significant reduction in the incidence of OAE and nodding syndrome. Treating epilepsy in onchocerciasis-endemic regions is challenging. More advocacy is needed to provide uninterrupted, free access to anti-seizure medication to persons with epilepsy in these remote, impoverished areas. It is crucial todevelop policies and increase funding for the prevention and treatment of OAE to reduce the associated burden of disease, notably via the establishment of morbidity management and disability prevention programs (MMDP). Moreover, effective collaboration between onchocerciasis elimination and mental health programs is imperative to alleviate the burden of OAE. This synergy promises reciprocal advantages and underscores the need for a comprehensive approach to address this multifaceted challenge.

Tau filaments from amyotrophic lateral sclerosis/parkinsonism-dementia complex adopt the CTE fold

The amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) of the island of Guam and the Kii peninsula of Japan is a fatal neurodegenerative disease of unknown cause that is characterized by the presence of abundant filamentous tau inclusions in brains and spinal cords. Here, we used electron cryo-microscopy to determine the structures of tau filaments from the cerebral cortex of three cases of ALS/PDC from Guam and eight cases from Kii, as well as from the spinal cord of two of the Guam cases. Tau filaments had the chronic traumatic encephalopathy (CTE) fold, with variable amounts of Type I and Type II filaments. Paired helical tau filaments were also found in three Kii cases and tau filaments with the corticobasal degeneration fold in one Kii case. We identified a new Type III CTE tau filament, where protofilaments pack against each other in an antiparallel fashion. ALS/PDC is the third known tauopathy with CTE-type filaments and abundant tau inclusions in cortical layers II/III, the others being CTE and subacute sclerosing panencephalitis. Because these tauopathies are believed to have environmental causes, our findings support the hypothesis that ALS/PDC is caused by exogenous factors.

Nodding syndrome is unlikely to be an autoimmune reaction to leiomodin-1 after infection by Onchocerca volvulus

Nodding syndrome is a neurological disease of children in northern Uganda. Infection with the nematode parasite Onchocerca volvulus has been epidemiologically implicated as the cause of the disease. It has been proposed that an autoantibody directed against the human protein leiomodin-1 cross reacts with a tropomyosin-like nematode protein, thus suggesting that nodding syndrome is an autoimmune brain disease due to extra-cerebral parasitism. This hypothesis is dependent on constitutive neuronal expression of leiomodin-1. We tested this hypothesis by studying the distribution of leiomodin-1 in the normal human brain and other human tissues using immunohistochemistry. We found that immunostaining for leiomodin-1 follows a smooth muscle cell specific pattern. In the brain, it is confined to the smooth muscle cells of cerebral blood vessels and is not generally present in neurons or glia. However, immunoreactivity was identified in human Purkinje cell membrane and the body wall of C. elegans (as a proxy for Onchocerca volvulus) but only when immunostained with an antibody recognizing the N-terminal of leiomodin-1. Homology between leiomodin-1 and tropomodulin, specifically at the N-terminus, could explain why leiomodin-1 antibody cross reactivity between human Purkinje cells and C. elegans. However, we cannot provide proof confirming that the immunoreactivity in the membranes of Purkinje cells is specifically caused by the expression of tropomodulin. To overcome this limitation, further investigations using additional immunohistochemical and biochemical studies are required to corroborate our findings and provide more comprehensive evidence. Nevertheless, our findings do not support to the autoimmunity hypothesis involving Onchocerca volvulus and leiomodin-1. To gain a more comprehensive understanding of the cause and pathogenesis of NS, it is essential to explore alternative hypotheses.

The onchocerciasis hypothesis of nodding syndrome

Nodding syndrome (NS) is a phenotypic presentation of onchocerciasis-associated epilepsy (OAE). OAE is an important public health problem in areas with high ongoing Onchocerca volvulus transmission. OAE, including NS, is preventable by strengthening onchocerciasis elimination programs. The presence of tau in OAE postmortem brains could be the consequence of neuroinflammation directly or indirectly induced by O. volvulus. Omics research is needed to investigate whether O. volvulus worms contain a neurotropic virus.

Tau Filaments from Amyotrophic Lateral Sclerosis/Parkinsonism-Dementia Complex (ALS/PDC) adopt the CTE Fold

The amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) of the island of Guam and the Kii peninsula of Japan is a fatal neurodegenerative disease of unknown cause that is characterised by the presence of abundant filamentous tau inclusions in brains and spinal cords. Here we used electron cryo-microscopy (cryo-EM) to determine the structures of tau filaments from the cerebral cortex of three cases of ALS/PDC from Guam and eight cases from Kii, as well as from the spinal cord of two of the Guam cases. Tau filaments had the chronic traumatic encephalopathy (CTE) fold, with variable amounts of Type I and Type II filaments. Paired helical tau filaments were also found in two Kii cases. We also identified a novel Type III CTE tau filament, where protofilaments pack against each other in an anti-parallel fashion. ALS/PDC is the third known tauopathy with CTE-type filaments and abundant tau inclusions in cortical layers II/III, the others being CTE and subacute sclerosing panencephalitis. Because these tauopathies are believed to have environmental causes, our findings support the hypothesis that ALS/PDC is caused by exogenous factors.

Onchocerciasis-associated epilepsy: an update and future perspectives

Onchocerciasis-associated epilepsy (OAE) is an important neglected public health problem in areas with high ongoing onchocerciasis transmission. The risk that children in such areas develop epilepsy is related to their Onchocerca volvulus microfilarial (mf) load. Before the implementation of mass treatment with ivermectin, microfilariae were detected in cerebrospinal fluid (CSF). More recently, neither O. volvulus microfilariae nor DNA were detected in CSF or brain tissue; however, these samples were obtained years after seizure onset. It is possible that during fever-induced increased blood-brain barrier permeability, microfilariae enter the brain and, upon dying, cause an inflammatory reaction inducing seizures. Including OAE in the onchocerciasis disease burden estimation may mobilise extra resources for onchocerciasis disease elimination and treatment/care of OAE-affected persons/families.

Preliminary seroprevalence study of neurotropic virus antibodies in Nodding syndrome

Nodding syndrome (NS) is a mostly East African pediatric epileptiform encephalopathy of unknown etiology that shares some clinical features with measles-associated subacute sclerosing panencephalitis (SSPE) and progressive rubella panencephalitis. Two independent studies in northern Uganda identified an association between NS and prior measles infection, while an earlier study in South Sudan found an inverse association. We report preliminary serologic analyses of antibodies to measles (MV), rubella (RV), HSV-1, and CMV viruses in northern Ugandan children with NS and Household (HC) and Community (CC) Controls. Only MV-positive titers were significantly different (3-fold and > 2-fold) in NS relative to HC and HC + CC, respectively. While these results are consistent with greater prior measles infection in Ugandan persons with NS, further studies are needed to determine whether Measles virus (MV) plays any role in the etiology and pathogenesis of NS. Resolving this issue will be invaluable for the thousands of children at risk for this devastating yet often neglected condition.

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Nodding syndrome (NS) is an enigmatic pediatric epileptiform encephalopathy.

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We report an association between NS and measles virus (MV)-positive titers.

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Further studies should assess whether MV plays any role in the etiology of NS.