Cognition and anatomy of adult Niemann-Pick disease type C: Insights for the Alzheimer field

Genetic forms of tauopathies: inherited causes and implications of Alzheimer's disease-like TAU pathology in primary and secondary tauopathies

Tauopathies are a heterogeneous group of neurologic diseases characterized by pathological axodendritic distribution, ectopic expression, and/or phosphorylation and aggregation of the microtubule-associated protein TAU, encoded by the gene MAPT. Neuronal dysfunction, dementia, and neurodegeneration are common features of these often detrimental diseases. A neurodegenerative disease is considered a primary tauopathy when MAPT mutations/haplotypes are its primary cause and/or TAU is the main pathological feature. In case TAU pathology is observed but superimposed by another pathological hallmark, the condition is classified as a secondary tauopathy. In some tauopathies (e.g. MAPT-associated frontotemporal dementia (FTD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Alzheimer's disease (AD)) TAU is recognized as a significant pathogenic driver of the disease. In many secondary tauopathies, including Parkinson's disease (PD) and Huntington's disease (HD), TAU is suggested to contribute to the development of dementia, but in others (e.g. Niemann-Pick disease (NPC)) TAU may only be a bystander. The genetic and pathological mechanisms underlying TAU pathology are often not fully understood. In this review, the genetic predispositions and variants associated with both primary and secondary tauopathies are examined in detail, assessing evidence for the role of TAU in these conditions. We highlight less common genetic forms of tauopathies to increase awareness for these disorders and the involvement of TAU in their pathology. This approach not only contributes to a deeper understanding of these conditions but may also lay the groundwork for potential TAU-based therapeutic interventions for various tauopathies.

Psychosis symptoms associated with Niemann-Pick disease type C

Niemann-Pick disease type C (NP-C) is a severe neurovisceral lipid storage disease that results in the accumulation of unesterified cholesterol in lysosomes or endosomes. The clinical presentations of NP-C are variable which include visceral symptoms, neurologic symptoms and psychiatric symptoms. Psychosis is the most common psychiatric manifestation of NP-C and is indistinguishable from a typical psychosis presentation of schizophrenia. The common psychotic presentations in NP-C include visual hallucinations, delusions, auditory hallucinations and thought disorders. Psychosis symptoms are more common in adult or adolescent-onset forms compared with pediatric-onset forms. The underlying pathophysiology of psychosis in NP-C is most probably due to dysconnectivity particularly between frontotemporal connectivity and subcortical structures. NP-C sometimes is mistaken for schizophrenia which causes delay in treatment due to lack of awareness and literature review. This review aims to summarize the relevant case reports on psychosis symptoms in NP-C and discuss the genetics and pathophysiology underlying the condition.

Neuropsychological assessment in Niemann-Pick disease type C: a systematic review

BACKGROUND

The neuropsychological profile of Niemann-Pick type C (NP-C) patients is characterized by an early deterioration in executive functions and attention. There are few studies on cognitive impairment and on neuropsychological assessment of NP-C disease. The purpose of this review is to analyze the studies on a psychological assessment for NP-C patients.

METHOD

This review aims to identify a neuropsychological assessment to evaluate cognitive domains and neuropsychological changes in these patients. There were a total of 73 articles. The search terms were identified as titles and abstracts. All articles were evaluated by title, abstract, and text.

RESULTS

Only four of the 73 articles were included because they met the criteria of our review. Furthermore, in these studies, possible diagnostic protocols are proposed on NP-C subjects.

DISCUSSION AND CONCLUSION

The cognitive impairment in NP-C has a negative impact on daily functioning and quality of life. Early diagnosis could identify cognitive deficits and promote cognitive interventions to improve the neuropsychological profile. The management of NP-C disease should be based on a multidisciplinary approach, to treating symptoms, preserving neurological functions, and guaranteeing the best possible quality of life. Early identification of neurological and psychological symptoms of the disease is necessary in order to decrease the progression of neurological disease and improve patient care and treatment outcomes. Furthermore, research should focus more on cognitive aspects, not only in the diagnostic process but also in the rehabilitation process.

Genodermatoses with behavioural sequelae

Children with genodermatoses are at an increased risk of developing behavioural disorders which may impart lasting damage on the individual and their family members. As such, early recognition of childhood mental health disorders via meticulous history taking, thorough physical examination, and disorder-specific testing is of paramount importance for timely and effective intervention. If carried out properly, prompt psychiatric screening and intervention can effectively mitigate, prevent or even reverse, the psychiatric sequela in question. To that end, this review aims to inform the concerned physician of the manifestations and treatment strategies relevant to the psychological sequelae of genodermatoses.

Assessment and rehabilitation of cognitive deficit in a Niemann-Pick type C disease patient

Niemann-Pick type C (NP-C) disease is a lipid storage disorder characterized by visceral (hepatosplenomegaly) and neurological symptoms: ataxia, dystonia, cognitive disorder, psychiatric disorder, and vertical supranuclear gaze palsy. Cognitive impairment is one of the core symptoms of NP-C disease, but there are few data about the cognitive rehabilitation treatment in NP-C patients. This case report aims to evaluate the effects of the cognitive rehabilitation treatment of a young woman affected by NP-C. Cognitive rehabilitation was performed with pc-based and paper and pencil exercises. We used a clinical approach that includes psychotherapy-based diagnostic and rehabilitation procedures and neuropsychological methods, using strategies to improve cognitive residual abilities. Our data showed an improvement of cognitive functions and quality of life after an intensive rehabilitation program.

Characterization of Dysphagia and Longitudinal Changes in Swallowing Function in Adults with Niemann-Pick Disease Type C Treated with Miglustat

Niemann-Pick disease type C (NPC) is a rare, autosomal recessive neurodegenerative disease, characterized by progressive psychiatric and neurological deficits. Neurological symptoms include cognitive decline and dysphagia. Aspiration pneumonia secondary to dysphagia is a leading cause of death in NPC. Miglustat is currently the only approved disease-specific treatment shown to be effective in stabilizing neurological symptoms. Miglustat has previously been reported to halt or improve early dysphagia and cognitive symptoms. Here we examine the characteristics of dysphagia, the relationship between dysphagia and the presence of cognitive impairment, and longitudinal changes in swallowing function during miglustat treatment in adult-and-adolescent-onset NPC. Retrospective analysis of videofluoroscopic swallow studies (VFSS) was completed for ten adults with NPC (mean age 28.44 years ± 9.34 years). Participants were recruited through the Royal Melbourne Hospital in Australia between 2008 and 2015. The Bethlehem Swallowing Scale and the Penetration-Aspiration Scale were used to quantify VFSS data. Dysphagia was present in 90% of participants at baseline with reduced lingual function and a delayed swallowing reflex as the most common symptoms. Swallow impairment appeared to stabilize during miglustat therapy for periods up to 66 months, with no significant changes in scores (p > 0.05). Data were in accordance with the literature and support the use of miglustat as an efficacious treatment for reducing swallowing impairment and stabilizing cognitive function. Findings provide detailed information on the impairments experienced by patients, give context to events leading to aspiration in NPC and, importantly, inform how management of dysphagia can complement pharmaceutical treatment.

Sphingolipids in Alzheimer's disease, how can we target them?

Altered levels of sphingolipids and their metabolites in the brain, and the related downstream effects on neuronal homeostasis and the immune system, provide a framework for understanding mechanisms in neurodegenerative disorders and for developing new intervention strategies. In this review we will discuss: the metabolites of sphingolipids that function as second messengers; and functional aberrations of the pathway resulting in Alzheimer's disease (AD) pathophysiology. Focusing on the central product of the sphingolipid pathway ceramide, we describ approaches to pharmacologically decrease ceramide levels in the brain and we argue on how the sphingolipid pathway may represent a new framework for developing novel intervention strategies in AD. We also highlight the possible use of clinical and non-clinical drugs to modulate the sphingolipid pathway and sphingolipid-related biological cascades.

Clinical and neurophysiological characteristics of heterozygous NPC1 carriers

Niemann-Pick disease type C (NPC) is an uncommon lysosomal storage disorder, which is characterized neuropathologically by cholinergic dysfunction and presents clinically with a broad series of neurological signs and symptoms. NPC is inherited as an autosomal recessive trait, caused by mutations in the NPC1 or NPC2 genes. However, recent reports have raised concerns on heterozygous NPC1 gene mutation carriers, which historically have been considered as clinically unaffected, occasionally presenting with clinical parkinsonian syndromes or dementia. In the present study, we aimed at comprehensively assessing clinical, biochemical, and neurophysiological features in heterozygous NPC1 gene mutation carriers. We assessed cholinergic intracortical circuits with transcranial magnetic stimulation, executive functions and plasma oxysterol levels in two families comprising two monozygotic twins with a homozygous NPC1 p.P888S mutation, four patients with a compound heterozygous p.E451K and p.G992W mutation, 10 heterozygous NPC1 p.P888S carriers, 1 heterozygous NPC1 p.E451K carrier, and 11 noncarrier family members. We observed a significant impairment in cholinergic circuits, evaluated with short-latency afferent inhibition (SAI), and executive abilities in homozygous/compound heterozygous patients and heterozygous asymptomatic NPC1 carriers, compared to noncarriers. Moreover, we reported a significant correlation between executive functions performances and both plasma oxysterol levels and neurophysiological parameters. These data suggest that heterozygous NPC1 carriers show subclinical deficits in cognition, possibly mediated by an impairment of cholinergic circuits, which in turn may mediate the onset of neurological disorders in a subset of patients.

Psychiatric and Cognitive Symptoms Associated with Niemann-Pick Type C Disease: Neurobiology and Management

Niemann-Pick disease type C (NPC) is a lysosomal storage disorder that presents with a spectrum of clinical manifestations from infancy and childhood or in early or mid-adulthood. Progressive neurological symptoms including ataxia, dystonia and vertical gaze palsy are a hallmark of the disease, and psychiatric symptoms such as psychosis and mood disorders are common. These latter symptoms often present early in the course of NPC and thus these patients are often diagnosed with a major psychotic or affective disorder before neurological and cognitive signs present and the diagnosis is revised. The commonalities and characteristics of psychotic symptoms in both NPC and schizophrenia may share neuronal pathways and mechanisms and provide potential targets for research in both disorders. The neurobiology of NPC and its relationship to the pattern of neuropsychiatric and cognitive symptoms is described in this review. A number of neurobiological models are proposed as mechanisms by which NPC causes psychiatric and cognitive symptoms, informed from models proposed in schizophrenia and other metabolic disorders. There are a number of symptomatic and illness-modifying treatments for NPC currently available. The current evidence is discussed; focussing on two medications which have shown promise, miglustat and hydroxypropyl-β-cyclodextrin.

Distinguishing neurocognitive deficits in adult patients with NP-C from early onset Alzheimer's dementia

BACKGROUND

Niemann-Pick disease type C (NP-C) is a rare, progressive neurodegenerative disease caused by mutations in the NPC1 or the NPC2 gene. Neurocognitive deficits are common in NP-C, particularly in patients with the adolescent/adult-onset form. As a disease-specific therapy is available, it is important to distinguish clinically between the cognitive profiles in NP-C and primary dementia (e.g., early Alzheimer's disease; eAD).

METHODS

In a prospective observational study, we directly compared the neurocognitive profiles of patients with confirmed NP-C (n = 7) and eAD (n = 15). All patients underwent neurocognitive assessment using dementia screening tests (mini-mental status examination [MMSE] and frontal assessment battery [FAB]) and an extensive battery of tests assessing verbal memory, visuoconstructive abilities, visual memory, executive functions and verbal fluency.

RESULTS

Overall cognitive impairment (MMSE) was significantly greater in eAD vs. NP-C (p = 0.010). The frequency of patients classified as cognitively 'impaired' was also significantly greater in eAD vs. NP-C (p = 0.025). Patients with NP-C showed relatively preserved verbal memory, but frequent impairment in visual memory, visuoconstruction, executive functions and in particular, verbal fluency. In the eAD group, a wider profile of more frequent and more severe neurocognitive deficits was seen, primarily featuring severe verbal and visual memory deficits along with major executive impairment. Delayed verbal memory recall was a particularly strong distinguishing factor between the two groups.

CONCLUSION

A combination of detailed yet easy-to-apply neurocognitive tests assessing verbal memory, executive functions and verbal fluency may help distinguish NP-C cases from those with primary dementia due to eAD.

Recent neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC

Niemann–Pick disease type C (NPC) is a rare autosomal recessive lysosomal storage disorder with extensive biological, molecular, and clinical heterogeneity. Recently, numerous studies have tried to shed light on the pathophysiology of the disease, highlighting possible disease pathways common to other neurodegenerative disorders, such as Alzheimer’s disease and frontotemporal dementia, and identifying possible candidate biomarkers for disease staging and response to treatment. Miglustat, which reversibly inhibits glycosphingolipid synthesis, has been licensed in the European Union and elsewhere for the treatment of NPC in both children and adults. A number of ongoing clinical trials might hold promise for the development of new treatments for NPC. The objective of the present work is to review and evaluate recent literature data in order to highlight the latest neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC pathophysiology. Furthermore, ongoing developments in disease-modifying treatments will be briefly discussed.

Cognitive impairment profile in adult patients with Niemann pick type C disease

Background

Cognitive impairment is one of the core symptoms of Niemann Pick type C (NPC) disease, but few data concerning the neuropsychological profile of NPC patients are available. The aim of our study was to characterize cognitive impairments in NPC disease and to assess the evolution of these symptoms and the impact of miglustat on cognitive follow-up.

Methods

We conducted a retrospective study of 21 adult patients diagnosed with NPC disease. Neuropsychological data (global cognitive efficiency, language, attention, executive functions, praxis, and visuoconstructive functions tests) were retrieved to describe the cognitive profile of patients. Cognitive impairment scores over time were assessed under treatment by miglustat.

Results

The majority of patients (90%) were impaired in one or more cognitive function. Executive functions and attention were the most impaired cognitive functions. Conversely, storage in the episodic memory was preserved in 61.5% of cases. Mean neuropsychological scores were stable during the period under miglustat (mean of 3.8 years).

Conclusions

This study is one of the first to assess the cognitive profile of adult NPC patients. This profile is not specific to attention and executive dysfunctions; however, the preservation of storage in the episodic memory is promising for cognitive remediation. Further studies are needed to confirm the role of miglustat on cognition, but in this study, patients were stable under this treatment.