Hyposmia: a possible biomarker of Parkinson's disease

Comparative Olfactory Profiles in Parkinson's Disease and Drug-Induced Parkinsonism

OBJECTIVE

Drug-induced parkinsonism (DIP) is a frequently encountered diagnostic possibility when considering Parkinson's disease (PD). While olfactory dysfunction is a common clinical feature in PD, the comparison of olfactory function between the two conditions remains insufficient. This study aimed to compare olfactory function, including threshold, discrimination, and identification (TDI) profiles, between PD and DIP.

METHODS

Consecutive patients with drug-naïve PD (n = 78) or DIP (n = 31) confirmed through dopamine transporter imaging were enrolled in this study. The YSK olfactory function (YOF) test, composed of TDI domains culturally familiar odorants to Koreans, was administered to all patients.

RESULTS

In the study population, patients with DIP were significantly older than patients with PD. Over 70% of patients in each group had hyposmia or anosmia, and there was no significant difference in the occurrence of olfactory dysfunction between the two groups. In addition, there were no differences in the total YOF score and threshold score between the two groups. Meanwhile, the PD group had a significantly lower discrimination and identification score than the DIP group after adjusting for age, sex, the existence of diabetes, disease duration, and cognitive function.

CONCLUSION

This study demonstrated that detailed olfactory profiles are different in PD and DIP, even though olfactory dysfunction can be observed in both conditions.

Impact of deep brain stimulation (DBS) on olfaction in Parkinson's disease: Clinical features and functional hypotheses

Deep brain stimulation (DBS) is a surgical therapy typically applied in Parkinson's disease (PD). The efficacity of DBS on the control of motor symptoms in PD is well grounded while the efficacity on non-motor symptoms is more controversial, especially on olfactory disorders (ODs). The present review shows that DBS does not improve hyposmia but can affect positively identification/discrimination scores in PD. The functional hypotheses suggest complex mechanisms in terms of cerebral connectivity and neurogenesis process which could act indirectly on the olfactory bulb and olfactory pathways related to specific cognitive olfactory tasks. The functional hypotheses also suggest complex mechanisms of cholinergic neurotransmitter interactions involved in these pathways. Finally, the impact of DBS on general cognitive functions in PD could also be beneficial to identification/discrimination tasks in PD.

Premotor, nonmotor and motor symptoms of Parkinson's Disease: A new clinical state of the art

Parkinson's Disease (PD) is a neurodegenerative disorder that affects dopaminergic neurons in the mesencephalic substantia nigra, causing a progressive clinical course characterized by pre-motor, non-motor and motor symptoms, which negatively impact the quality of life of patients and cause high health care costs. Therefore, the present study aims to discuss the clinical manifestations of PD and to make a correlation with the gut-brain (GB) axis, approaching epidemiology and therapeutic perspectives, to better understand its clinical progression and identify symptoms early. A literature review was performed regarding the association between clinical progression, the gut-brain axis, epidemiology, and therapeutic perspectives, in addition to detailing pre-motor, non-motor symptoms (neuropsychiatric, cognitive, autonomic, sleep disorders, sensory abnormalities) and cardinal motor symptoms. Therefore, this article addresses a topic of extreme relevance, since the previously mentioned clinical manifestations (pre-motor and non-motor) can often act as prodromal markers for the early diagnosis of PD and may precede it by up to 20 years.

Prevalence of Malnutrition in Patients with Parkinson's Disease: A Systematic Review

OBJECTIVES

This systematic review analyzed the prevalence of malnutrition in patients with Parkinson's Disease.

STUDY DESIGN

a systematic review.

METHOD

Four databases-Cochrane, PubMed, Embase and Web of Science-were searched from October 2021 to June 2022 by two independent researchers. The inclusion criteria were as follows: patients above 18 years old with confirmed Parkinson's Disease, performed screening nutritional assessment, cohort studies, case-control studies, and cross-sectional studies. Patients without Parkinson's Disease and with other parkinsonian syndromes were excluded.

RESULTS

49 studies were included in this systematic review. Patients ranged in age from 20 to 96 years. There were 5613 subjects included. According to Mini Nutritional Assessment, 23.9% (n = 634) participants were at risk of malnutrition and 11.1% (n = 294) were malnourished. According to BMI score, most patients were either obese or overweight.

CONCLUSIONS

the prevalence of malnutrition or risk of malnutrition in the study group was significant. Therefore, more specific and detailed studies on the prevalence of malnutrition in patients with Parkinson's Disease are needed.

A Comprehensive Assessment of Qualitative and Quantitative Prodromal Parkinsonian Features in Carriers of Gaucher Disease-Identifying Those at the Greatest Risk

Carriers of GBA1 gene variants have a significant risk of developing Parkinson’s disease (PD). A cohort study of GBA carriers between 40−75 years of age was initiated to study the presence of prodromal PD features. Participants underwent non-invasive tests to assess different domains of PD. Ninety-eight unrelated GBA carriers were enrolled (43 males) at a median age (range) of 51 (40−74) years; 71 carried the N370S variant (c.1226A > G) and 25 had a positive family history of PD. The Montreal Cognitive Assessment (MoCA) was the most frequently abnormal (23.7%, 95% CI 15.7−33.4%), followed by the ultrasound hyperechogenicity (22%, 95% CI 14−32%), Unified Parkinson’s Disease Rating Scale part III (UPDRS-III) (17.2%, 95% CI 10.2−26.4%), smell assessment (12.4%, 95% CI 6.6−20.6%) and abnormalities in sleep questionnaires (11%, 95% CI 5.7−19.4%). Significant correlations were found between tests from different domains. To define the risk for PD, we assessed the bottom 10th percentile of each prodromal test, defining this level as “abnormal”. Then we calculated the percentage of “abnormal” tests for each subject; the median (range) was 4.55 (0−43.5%). Twenty-two subjects had more than 15% “abnormal” tests. The limitations of the study included ascertainment bias of individuals with GBA-related PD in relatives, some incomplete data due to technical issues, and a lack of well-characterized normal value ranges in some tests. We plan to enroll additional participants and conduct longitudinal follow-up assessments to build a model for identifying individuals at risk for PD and investigate interventions aiming to delay the onset or perhaps to prevent full-blown PD.

REM sleep behavior and olfactory dysfunction: improving the utility and translation of animal models in the search for neuroprotective therapies for Parkinson's disease

Parkinson's disease (PD) is a heterogeneous neurodegenerative disease that belongs to the family of synucleiopathies, varying in age, symptoms and progression. Hallmark of the disease is the accumulation of misfolded α-synuclein protein (α-Syn) in neuronal and non-neuronal brain cells. In past decades, diagnosis and treatment of PD has focused on motor deficits, which for the clinical endpoint, have contributed to the prevalence of deficits in the nigrostriatal dopaminergic system and animal models related to motor behavior to study disease. However, clinical trials have failed to translate results from animal models into effective treatments. PD as a multisystem disorder therefore requires additional assessment of motor and non-motor symptoms. Braak's staging revealed early α-Syn pathology in pontine brainstem and olfactory circuits controlling rapid eye movement sleep behavior disorder (RBD) and olfaction, respectively. Recent converging evidence from multicenter clinical studies supports that RBD is the most important risk factor for prodromal PD and the conduct of neuroprotective therapeutic trials in RBD-enriched cohorts has been recommended. Animal models of RBD and olfaction dysfunction can aid to fill the gap in translational research.

Role of medicinal plants in inhibiting SARS-CoV-2 and in the management of post-COVID-19 complications

BACKGROUND

The worldwide corona virus disease outbreak, generally known as COVID-19 pandemic outbreak resulted in a major health crisis globally. The morbidity and transmission modality of COVID-19 appear more severe and uncontrollable. The respiratory failure and following cardiovascular complications are the main pathophysiology of this deadly disease. Several therapeutic strategies are put forward for the development of safe and effective treatment against SARS-CoV-2 virus from the pharmacological view point but till date there are no specific treatment regimen developed for this viral infection.

PURPOSE

The present review emphasizes the role of herbs and herbs-derived secondary metabolites in inhibiting SARS-CoV-2 virus and also for the management of post-COVID-19 related complications. This approach will foster and ensure the safeguards of using medicinal plant resources to support the healthcare system. Plant-derived phytochemicals have already been reported to prevent the viral infection and to overcome the post-COVID complications like parkinsonism, kidney and heart failure, liver and lungs injury and mental problems. In this review, we explored mechanistic approaches of herbal medicines and their phytocomponenets as antiviral and post-COVID complications by modulating the immunological and inflammatory states.

STUDY DESIGN

Studies related to diagnosis and treatment guidelines issued for COVID-19 by different traditional system of medicine were included. The information was gathered from pharmacological or non-pharmacological interventions approaches. The gathered information sorted based on therapeutic application of herbs and their components against SARSCoV-2 and COVID-19 related complications.

METHODS

A systemic search of published literature was conducted from 2003 to 2021 using different literature database like Google Scholar, PubMed, Science Direct, Scopus and Web of Science to emphasize relevant articles on medicinal plants against SARS-CoV-2 viral infection and Post-COVID related complications.

RESULTS

Collected published literature from 2003 onwards yielded with total 625 articles, from more than 18 countries. Among these 625 articles, more than 95 medicinal plants and 25 active phytomolecules belong to 48 plant families. Reports on the therapeutic activity of the medicinal plants belong to the Lamiaceae family (11 reports), which was found to be maximum reported from 4 different countries including India, China, Australia, and Morocco. Other reports on the medicinal plant of Asteraceae (7 reports), Fabaceae (8 reports), Piperaceae (3 reports), Zingiberaceae (3 reports), Ranunculaceae (3 reports), Meliaceae (4 reports) were found, which can be explored for the development of safe and efficacious products targeting COVID-19.

CONCLUSION

Keeping in mind that the natural alternatives are in the priority for the management and prevention of the COVID-19, the present review may help to develop an alternative approach for the management of COVID-19 viral infection and post-COVID complications from a mechanistic point of view.

Functional Covariance Connectivity of Gray and White Matter in Olfactory-Related Brain Regions in Parkinson’s Disease

Before the onset of motor symptoms, Parkinson’s disease (PD) involves dysfunction of the anterior olfactory nucleus and olfactory bulb, causing olfactory disturbance, commonly resulting in hyposmia in the early stages of PD. Accumulating evidence has shown that blood oxygen level dependent (BOLD) signals in white matter are altered by olfactory disorders and related stimuli, and the signal changes in brain white matter pathways show a certain degree of specificity, which can reflect changes of early olfactory dysfunction in Parkinson’s disease. In this study, we apply the functional covariance connectivity (FCC) method to decode FCC of gray and white matter in olfactory-related brain regions in Parkinson’s disease. Our results show that the dorsolateral prefrontal, anterior entorhinal cortex and fronto-orbital cortices in the gray matter have abnormal connectivity with the posterior corona radiata and superior corona radiata in white matter in patients with Parkinson’s hyposmia. The functional covariance connection strength (FCS) of the right dorsolateral prefrontal cortex and white matter, and the covariance connection strength of the left superior corona radiata and gray matter function have potential diagnostic value. These results demonstrate that alterations in FCC of gray and white matter in olfactory-related brain regions can reflect the change of olfactory function in the early stages of Parkinson’s disease, indicating that it could be a potential neuroimaging marker for early diagnosis.

Olfactory Bulb D2/D3 Receptor Availability after Intrastriatal Botulinum Neurotoxin-A Injection in a Unilateral 6-OHDA Rat Model of Parkinson's Disease

Olfactory deficits occur as early non-motor symptoms of idiopathic Parkinson's disease (PD) in humans. The first central relay of the olfactory pathway, the olfactory bulb (OB), depends, among other things, on an intact, functional crosstalk between dopaminergic interneurons and dopamine receptors (D2/D3R). In rats, hemiparkinsonism (hemi-PD) can be induced by unilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB), disrupting dopaminergic neurons of the substantia nigra pars compacta (SNpc). In a previous study, we showed that subsequent injection of botulinum neurotoxin-A (BoNT-A) into the striatum can reverse most of the pathological motor symptoms and normalize the D2/D3R availability. To determine whether this rat model is suitable to explain olfactory deficits that occur in humans with PD, we examined the availability of D2/D3R by longitudinal [18F]fallypride-PET/CT, the density of tyrosine hydroxylase immunoreactivity in the OB, olfactory performance by an orienting odor identification test adapted for rats, and a connectome analysis. PET/CT and immunohistochemical data remained largely unchanged after 6-OHDA lesion in experimental animals, suggesting that outcomes of the 6-OHDA hemi-PD rat model do not completely explain olfactory deficits in humans. However, after subsequent ipsilateral BoNT-A injection into the striatum, a significant 8.5% increase of the D2/D3R availability in the ipsilateral OB and concomitant improvement of olfactory performance were detectable. Based on tract-tracing meta-analysis, we speculate that this may be due to indirect connections between the striatum and the OB.

Spotlight on non-motor symptoms and Covid-19

The Coronavirus Disease 2019 (Covid-19) pandemic has profoundly affected the quality of life (QoL) and health of the general population globally over the past 2 years, with a clear impact on people with Parkinson's Disease (PwP, PD). Non-motor symptoms have been widely acknowledged to hold a vital part in the clinical spectrum of PD, and, although often underrecognized, they significantly contribute to patients' and their caregivers' QoL. Up to now, there have been numerous reports of newly emerging or acutely deteriorating non-motor symptoms in PwP who had been infected by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), while some of these symptoms, like fatigue, pain, depression, anxiety and cognitive impairment, have also been identified as part of the long-COVID syndrome due to their persistent nature. The subjacent mechanisms, mediating the appearance or progression of non-motor symptoms in the context of Covid-19, although probably multifactorial in origin, remain largely unknown. Such mechanisms might be, at least partly, related solely to the viral infection per se or the lifestyle changes imposed during the pandemic, as many of the non-motor symptoms seem to be prevalent even among Covid-19 patients without PD. Here, we summarize the available evidence and implications of Covid-19 in non-motor PD symptoms in the acute and chronic, if applicable, phase of the infection, with a special reference on studies of PwP.

Evaluation of Olfactory Function by Iranian Smell Diagnostic Test in Patients with Parkinson's disease in North of Iran

Introduction

Parkinson's disease is a neurodegenerative and multisystem disorder affecting systems more than the motor system. The olfactory disorder is an early non-motor symptom of Parkinson's disease.

Materials and Methods

The present study was conducted on 110 patients aged 50-95 years with a diagnosis of Parkinson's disease referred to the Neurology Clinic of Babol University of Medical Sciences between 2018-2019. The control group consisted of 50-95-year-old non-neurological patients who were matched for age and gender with patients with Parkinson's disease. Data were collected by examination, demographic and clinical information questionnaire (duration of disease, the severity of disease, symptom index), as well as Iranian smell diagnostic test. A p-value less than 0.05 was considered statistically significant.

Results

The mean age scores of Parkinson's disease and control groups were obtained at 69±9 and 66±9 years, respectively. The mean duration of the disease was 5 years. Patients with Parkinson's disease scored lower on the Iranian smell test, and olfactory function was significantly reduced in the case group (P<0.001). Based on the results, olfactory function in patients with Parkinson's disease was not significantly correlated with gender, marital status, education, place of residence, and occupation(P<0.05). Only olfactory dysfunction was increased with age (P=0.01). In addition, olfactory dysfunction showed no significant relationship with severity of disease, duration of disease, and clinical index sign. Rapid Iranian smell test with a cut-off of 3.5% had a sensitivity of 87.3% and a specificity of 66.4%.

Conclusion

According to the obtained results, olfactory dysfunction is an important non-motor and a primary symptom in patients with Parkinson's disease and is not related to the duration and severity of motor symptoms and symptom index.

Systematic Review: Quantitative Susceptibility Mapping (QSM) of Brain Iron Profile in Neurodegenerative Diseases

Iron has been increasingly implicated in the pathology of neurodegenerative diseases. In the past decade, development of the new magnetic resonance imaging technique, quantitative susceptibility mapping (QSM), has enabled for the more comprehensive investigation of iron distribution in the brain. The aim of this systematic review was to provide a synthesis of the findings from existing QSM studies in neurodegenerative diseases. We identified 80 records by searching MEDLINE, Embase, Scopus, and PsycInfo databases. The disorders investigated in these studies included Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Wilson's disease, Huntington's disease, Friedreich's ataxia, spinocerebellar ataxia, Fabry disease, myotonic dystrophy, pantothenate-kinase-associated neurodegeneration, and mitochondrial membrane protein-associated neurodegeneration. As a general pattern, QSM revealed increased magnetic susceptibility (suggestive of increased iron content) in the brain regions associated with the pathology of each disorder, such as the amygdala and caudate nucleus in Alzheimer's disease, the substantia nigra in Parkinson's disease, motor cortex in amyotrophic lateral sclerosis, basal ganglia in Huntington's disease, and cerebellar dentate nucleus in Friedreich's ataxia. Furthermore, the increased magnetic susceptibility correlated with disease duration and severity of clinical features in some disorders. Although the number of studies is still limited in most of the neurodegenerative diseases, the existing evidence suggests that QSM can be a promising tool in the investigation of neurodegeneration.

Premotor Parkinson's disease: Overview of clinical symptoms and current diagnostic methods

Parkinson's disease (PD) is characterized by typical motor symptoms. However, recent studies show several non-motor features that may precede the development of the motor symptoms of PD. The best known premotor symptoms include hyposmia, REM sleep behavior disorder (RBD), constipation, and depression; other symptoms are excessive daytime somnolence, orthostatic hypotension and symptomatic hypotension, erectile or urinary dysfunction, musculoskeletal symptoms, pain, and global cognitive deficit. In this review, we summarize currently available diagnostic methods for these symptoms. We also briefly summarize neuroimaging, polyneuropathy, peripheral markers, and cerebrospinal fluid biomarkers that may be used in the early diagnosis of PD.

Parkinson's disease and the non-motor symptoms: hyposmia, weight loss, osteosarcopenia

Non-motor symptoms (NMSs) are common in Parkinson's disease (PD) and can precede, sometimes for several years. NMSs include, other than gastrointestinal symptoms like constipation and dysphagia, also hyposmia, weight loss and osteosarcopenia. These three NMSs seem to be inter-related and affect patients' health and quality of life. Unfortunately, patients with these symptoms usually are not initially seen by a neurologist, and by the time they are consulted, nearly ~ 80% of the dopaminergic neurons in the substantia nigra have died. To date, no guidelines exist for screening, assessment and management of NMSs in general. A better understanding of these specific NMSs, likely in the context of others, will make it possible to approach and optimise the treatment of the motor symptoms thereby enhancing the welfare of PD patients. Identifying the NMSs could be very helpful, and among them, hyposmia, weight loss and osteosarcopenia may play an important role in solving the limitations in the diagnosis of PD. A strict collaboration between general practitioners, clinicians, geriatricians and neurologists can be one approach towards the diagnosis of pre-PD. Waiting until the motor symptoms develop and the patient is finally visited by the neurologist could be too late, considering the catastrophic prognosis of the disease.

The Evolution-Driven Signature of Parkinson's Disease

In this review, we approach Parkinson's disease (PD) in the context of an evolutionary mismatch of central nervous system functions. The neurons at risk have hyperbranched axons, extensive transmitter release sites, display spontaneous spiking, and elevated mitochondrial stress. They function in networks largely unchanged throughout vertebrate evolution, but now connecting to the expanded human cortex. Their breakdown is favoured by longevity. At the cellular level, mitochondrial dysfunction starts at the synapses, then involves axons and cell bodies. At the behavioural level, network dysfunctions provoke the core motor syndrome of parkinsonism including freezing and failed gait automatization, and non-motor deficits including inactive blindsight and autonomic dysregulation. The proposed evolutionary re-interpretation of PD-prone cellular phenotypes and of prototypical clinical symptoms allows a new conceptual framework for future research.

Olfactory Dysfunction in Familial and Sporadic Parkinson's Disease

This minireview discusses our current understanding of the olfactory dysfunction that is frequently observed in sporadic and familial forms of Parkinson's disease and parkinsonian syndromes. We review the salient characteristics of olfactory dysfunction in these conditions, discussing its prevalence and characteristics, how neuronal processes and circuits are altered in Parkinson's disease, and what is assessed by clinically used measures of olfactory function. We highlight how studies of monogenic Parkinson's disease and investigations in ethnically diverse populations have contributed to understanding the mechanisms underlying olfactory dysfunction. Furthermore, we discuss how imaging and system-level approaches have been used to understand the pathogenesis of olfactory dysfunction. We discuss the challenging, remaining gaps in understanding the basis of olfactory dysfunction in neurodegeneration. We propose that insights could be obtained by following longitudinal cohorts with familial forms of Parkinson's disease using a combination of approaches: a multifaceted longitudinal assessment of olfactory function during disease progression is essential to identify not only how dysfunction arises, but also to address its relationship to motor and non-motor Parkinson's disease symptoms. An assessment of cohorts having monogenic forms of Parkinson's disease, available within the Genetic Epidemiology of Parkinson's Disease (GEoPD), as well as other international consortia, will have heuristic value in addressing the complexity of olfactory dysfunction in the context of the neurodegenerative process. This will inform our understanding of Parkinson's disease as a multisystem disorder and facilitate the more effective use of olfactory dysfunction assessment in identifying prodromal Parkinson's disease and understanding disease progression.

Parkinson's Disease: Available Clinical and Promising Omics Tests for Diagnostics, Disease Risk Assessment, and Pharmacotherapy Personalization

Parkinson's disease is the second most frequent neurodegenerative disease, representing a significant medical and socio-economic problem. Modern medicine still has no answer to the question of why Parkinson's disease develops and whether it is possible to develop an effective system of prevention. Therefore, active work is currently underway to find ways to assess the risks of the disease, as well as a means to extend the life of patients and improve its quality. Modern studies aim to create a method of assessing the risk of occurrence of Parkinson's disease (PD), to search for the specific ways of correction of biochemical disorders occurring in the prodromal stage of Parkinson's disease, and to personalize approaches to antiparkinsonian pharmacotherapy. In this review, we summarized all available clinically approved tests and techniques for PD diagnostics. Then, we reviewed major improvements and recent advancements in genomics, transcriptomics, and proteomics studies and application of metabolomics in PD research, and discussed the major metabolomics findings for diagnostics and therapy of the disease.

Clinical Progression of Parkinson's Disease: Insights from the NINDS Common Data Elements

BACKGROUND/OBJECTIVE

To synchronize data collection, the National Institute of Neurological Disorders and Stroke (NINDS) recommended Common Data Elements (CDEs) for use in Parkinson's disease (PD) research. This study delineated the progression patterns of these CDEs in a cohort of PD patients.

METHODS

One hundred-twenty-five PD patients participated in the PD Biomarker Program (PDBP) at Penn State. CDEs, including MDS-Unified PD Rating Scale (UPDRS)-total, questionnaire-based non-motor (-I) and motor (-II), and rater-based motor (-III) subscales; Montreal Cognitive Assessment (MoCA); Hamilton Depression Rating Scale (HDRS); University of Pennsylvania Smell Identification Test (UPSIT); and PD Questionnaire (PDQ-39) were obtained at baseline and three annual follow-ups. Annual change was delineated for PD or subgroups [early = PDE, disease duration (DD) <1 y; middle = PDM, DD = 1-5 y; and late = PDL, DD > 5 y] using mixed effects model analyses.

RESULTS

UPDRS-total, -II, and PDQ-39 scores increased significantly, and UPSIT decreased, whereas UPDRS-I, -III, MoCA, and HDRS did not change, over 36 months in the overall PD cohort. In the PDE subgroup, UPDRS-II increased and UPSIT decreased significantly, whereas MoCA and UPSIT decreased significantly in the PDM subgroup. In the PDL subgroup, UPDRS-II and PDQ-39 increased significantly. Other metrics within each individual subgroup did not change. Sensitivity analyses using subjects with complete data confirmed these findings.

CONCLUSION

Among CDEs, UPDRS-total, -II, PDQ-39, and UPSIT all are sensitive metrics to track PD progression. Subgroup analyses revealed that these CDEs have distinct stage-dependent sensitivities, with UPSIT for DD < 5 y, PDQ-39 for DD > 5 y, UPDRS-II for early (DD < 1) or later stages (DD > 5).

Hyposmia as a Predictive Marker of Parkinson's Disease: A Systematic Review and Meta-Analysis

Background

Hyposmia is one of the most common and best-characterized conditions that is also one of the first nonmotor features of Parkinson's disease (PD). The association of hyposmia with PD is widely accepted; however the likelihood of developing PD is unclear. Our meta-analysis aimed to investigate the risk of PD in individuals with hyposmia.

Methods

Prospective studies on humans published before December 4^th, 2018, were searched for in PubMed, Embase, Web of Science, and Cochrane Library databases. Two independent reviewers screened studies for inclusion and extracted data. We assessed the quality of studies using the Newcastle–Ottawa Scale and pooled data for analysis using random-effects models.

Results

Of the 1774 studies retrieved, seven met the inclusion criteria for this review. A total of 3272 hyposmia and 176 PD events were reported over follow-up periods ranging from 3 to 17 years. Hyposmia was associated with a 3.84-fold risk of developing PD (pooled relative risk: 3.84, 95% CI 2.12−6.95). Subgroup analyses identified few differences between different hyposmia assessment methodologies and follow-up periods.

Conclusions

Our findings suggest that deficiencies in olfaction are associated with an increased risk of developing PD. Future studies are needed to investigate whether hyposmia is a promising and feasible biomarker for the early diagnosis of PD.

Nicotine improved the olfactory impairment in MPTP-induced mouse model of Parkinson's disease

Olfactory impairment is an early feature of patients with Parkinson's disease (PD). Retrospective epidemiological studies reported lower scores on the University of Pennsylvania Smell Identification Test (UPSIT) in non-smokers than smokers with PD and showed an inverse correlation between susceptibility to PD and a person's history of smoking. But the mechanisms by which cigarettes affect olfaction in PD are not fully understood. So we investigated the effect of nicotine on the olfactory function in 1-methyl-4-phenyl-1, 2, 3, 6 tetrahydropyridine (MPTP)-treated mice. We observed that nicotine improved locomotor activity and protection against dopaminergic neuron loss in the midbrain in MPTP-treated mice. Compared to controls, MPTP-treated mice showed a deficit of odor discrimination and odor detection, which were alleviated by nicotine treatment. But no significant changes were found in olfactory memory in MPTP-treated mice. Moreover, we detected a marked decrease of Choline acetyltransferase (ChAT) expression in the olfactory bulb (OB) in MPTP-treated mice, which was also attenuated by nicotine administration. In addition, nicotine ameliorated the loss of cholinergic neurons and dopaminergic innervation in the horizontal limb of the diagonal band (HDB), which is the primary origin of cholinergic input to the OB. Our results suggested that nicotine could improve the olfactory impairment by protecting cholinergic systems in the OB of MPTP-treated mice. And nicotine protection of cholinergic systems in the OB is relevant to attenuating dopaminergic neuron loss in the midbrain and HDB.

Partial depletion of dopaminergic neurons in the substantia nigra impairs olfaction and alters neural activity in the olfactory bulb

Olfactory dysfunction is a major non-motor symptom that appears during the early stages of Parkinson’s Disease (PD), a neurodegenerative disorder characterized by loss of dopaminergic neurons in the substantia nigra (SN). Depletion of SN dopaminergic neurons by 6-hydroxydopamine (6-OHDA) is widely used as a model for PD and ultimately results in motor deficits. However, it is largely unknown whether olfactory behavior and, more importantly, neural activity in the olfactory bulb (OB) are impaired prior to the appearance of motor deficits. We partially depleted the SN dopaminergic population in mice by injection of 6-OHDA. Seven days after injection of 6-OHDA, motor ability was unchanged but olfactory-driven behaviors were significantly impaired. Injection of 6-OHDA into the SN significantly increased the power of the ongoing local field potential in the OB for all frequency bands, and decreased odor-evoked excitatory beta responses and inhibitory high-gamma responses. Moreover, 6-OHDA treatment led to increased odor-evoked calcium responses in the mitral cells in the OB of awake mice. These data suggest that the olfactory deficits caused by depletion of the SN dopaminergic population are likely due to abnormal hyperactivity of the mitral cells in the OB.

Diagnostic biomarkers for Parkinson's disease at a glance: where are we?

Parkinson's disease (PD) is a neurodegenerative disorder whose aetiology remains unclear: degeneration involves several neurotransmission systems, resulting in a heterogeneous disease characterized by motor and non-motor symptoms. PD causes progressive disability that responds only to symptomatic therapies. Future advances include neuroprotective strategies for use in at-risk populations before the clinical onset of disease, hence the continuing need to identify reliable biomarkers that can facilitate the clinical diagnosis of PD. In this evaluative review, we summarize information on potential diagnostic biomarkers for use in the clinical and preclinical stages of PD.

Impairment in Respiratory Function Contributes to Olfactory Impairment in Amyotrophic Lateral Sclerosis

Background

Nonmotor symptoms are very common in neurodegenerative diseases. In patients suffering from amyotrophic lateral sclerosis (ALS), olfactory dysfunction was first reported more than 20 years ago; however, its pathophysiological correlates and further implications remain elusive.

Methods

In this so far largest case-control study, we analyzed olfactory performance with the "Sniffin' Sticks," a validated olfactory testing kit used in clinical routine. This test kit was designed to investigate different qualities of olfaction including odor threshold, odor discrimination, and odor identification.

Results

ALS patients were mildly but significantly impaired in TDI score, the composite of the three subtests (ALS 27.7 ± 7.9, Controls 32.3 ± 5.8). In contrast to Parkinson's disease, ALS patients did not show impaired performance in the suprathreshold tests identification and discrimination. However, the odor threshold was markedly decreased (ALS 6.0 ± 3.4, Controls 8.77 ± 3.6). This pattern of olfactory loss resembles sinonasal diseases, where olfactory dysfunction results from impeded odorant transmission to the olfactory cleft. The evaluation of medical history and clinical data of ALS patients showed that patients with perception of dyspnea (TDI 25.7 ± 8.0) performed significantly worse in olfactory testing compared to those who did not (TDI 30.0 ± 7.4). In line with that, we found that in patients with preserved respiratory function (vital capacity >70% of index value), olfactory performance did not differ from healthy controls.

Conclusion

These findings suggest that the mild impairment of olfaction in patients suffering from ALS should at least partly be considered as a consequence of impaired respiratory function, and odor threshold might be a marker of respiratory dysfunction in ALS.

Can Biomarkers Help the Early Diagnosis of Parkinson's Disease?

Parkinson's disease (PD) is a complex neurodegenerative disease with progressive loss of dopamine neurons. PD patients usually manifest a series of motor and non-motor symptoms. In order to provide better early diagnosis and subsequent disease-modifying therapies for PD patients, there is an urgent need to identify sensitive and specific biomarkers. Biomarkers can be divided into four categories: clinical, imaging, biochemical, and genetic. Ideal biomarkers not only improve our understanding of PD pathogenesis and progression, but also provide benefits for early risk evaluation and clinical diagnosis of PD. Although many efforts have been made and several biomarkers have been extensively investigated, few if any have been found useful for early diagnosis. Here, we summarize recent developments in the discovered biomarkers of PD and discuss their merits and limitations for the early diagnosis of PD.

Transcription Factors: Potential Cell Death Markers in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease with a long preclinical phase. The continuous loss of dopaminergic (DA) neurons is one of the pathogenic hallmarks of PD. Diagnosis largely depends on clinical observation, but motor dysfunctions do not emerge until 70%-80% of the nigrostriatal nerve terminals have been destroyed. Therefore, a biomarker that indicates the degeneration of DA neurons is urgently needed. Transcription factors are sequence-specific DNA-binding proteins that regulate RNA synthesis from a DNA template. The precise control of gene expression plays a critical role in the development, maintenance, and survival of cells, including DA neurons. Deficiency of certain transcription factors has been associated with DA neuron loss and PD. In this review, we focus on some transcription factors and discuss their structure, function, mechanisms of neuroprotection, and their potential for use as biomarkers indicating the degeneration of DA neurons.

Parkinson's disease biomarkers: perspective from the NINDS Parkinson's Disease Biomarkers Program

Biomarkers for Parkinson's disease (PD) diagnosis, prognostication and clinical trial cohort selection are an urgent need. While many promising markers have been discovered through the National Institute of Neurological Disorders and Stroke Parkinson's Disease Biomarker Program (PDBP) and other mechanisms, no single PD marker or set of markers are ready for clinical use. Here we discuss the current state of biomarker discovery for platforms relevant to PDBP. We discuss the role of the PDBP in PD biomarker identification and present guidelines to facilitate their development. These guidelines include: harmonizing procedures for biofluid acquisition and clinical assessments, replication of the most promising biomarkers, support and encouragement of publications that report negative findings, longitudinal follow-up of current cohorts including the PDBP, testing of wearable technologies to capture readouts between study visits and development of recently diagnosed (de novo) cohorts to foster identification of the earliest markers of disease onset.

Odorants could elicit repair processes in melanized neuronal and skin cells

The expression of ectopic olfactory receptors (ORs) in melanized cells, such as the human brain nigrostriatal dopaminergic neurons and skin melanocytes, is here pointed out. ORs are recognized to regulate skin melanogenesis, whereas OR expression in the dopaminergic neurons, characterized by accumulation of pigment neuromelanin, is downregulated in Parkinson's disease. Furthermore, the correlation between the pigmentation process and the dopamine pathway through α-synuclein expression is also highlighted. Purposely, these ORs are suggested as therapeutic target for neurodegenerative diseases related to the pigmentation disorders. Based on this evidence, a possible way of turning odorants into drugs, acting on three specific olfactory receptors, OR51E2, OR2AT4 and VN1R1, is thus introduced. Various odorous molecules are shown to interact with these ORs and their therapeutic potential against melanogenic and neurodegenerative dysfunctions, including melanoma and Parkinson's disease, is suggested. Finally, a direct functional link between olfactory and endocrine systems in human brain through VN1R1 is proposed, helping to counteract female susceptibility to Parkinson's disease in quiescent life.

Assessment of Olfactory Function in MAPT-Associated Neurodegenerative Disease Reveals Odor-Identification Irreproducibility as a Non-Disease-Specific, General Characteristic of Olfactory Dysfunction

Olfactory dysfunction is associated with normal aging, multiple neurodegenerative disorders, including Parkinson's disease, Lewy body disease and Alzheimer's disease, and other diseases such as diabetes, sleep apnea and the autoimmune disease myasthenia gravis. The wide spectrum of neurodegenerative disorders associated with olfactory dysfunction suggests different, potentially overlapping, underlying pathophysiologies. Studying olfactory dysfunction in presymptomatic carriers of mutations known to cause familial parkinsonism provides unique opportunities to understand the role of genetic factors, delineate the salient characteristics of the onset of olfactory dysfunction, and understand when it starts relative to motor and cognitive symptoms. We evaluated olfactory dysfunction in 28 carriers of two MAPT mutations (p.N279K, p.P301L), which cause frontotemporal dementia with parkinsonism, using the University of Pennsylvania Smell Identification Test. Olfactory dysfunction in carriers does not appear to be allele specific, but is strongly age-dependent and precedes symptomatic onset. Severe olfactory dysfunction, however, is not a fully penetrant trait at the time of symptom onset. Principal component analysis revealed that olfactory dysfunction is not odor-class specific, even though individual odor responses cluster kindred members according to genetic and disease status. Strikingly, carriers with incipient olfactory dysfunction show poor inter-test consistency among the sets of odors identified incorrectly in successive replicate tests, even before severe olfactory dysfunction appears. Furthermore, when 78 individuals without neurodegenerative disease and 14 individuals with sporadic Parkinson's disease were evaluated twice at a one-year interval using the Brief Smell Identification Test, the majority also showed inconsistency in the sets of odors they identified incorrectly, independent of age and cognitive status. While these findings may reflect the limitations of these tests used and the sample sizes, olfactory dysfunction appears to be associated with the inability to identify odors reliably and consistently, not with the loss of an ability to identify specific odors. Irreproducibility in odor identification appears to be a non-disease-specific, general feature of olfactory dysfunction that is accelerated or accentuated in neurodegenerative disease. It may reflect a fundamental organizational principle of the olfactory system, which is more "error-prone" than other sensory systems.

Effect of the antiepileptic therapy on olfactory disorders associated with mesial temporal sclerosis

Parosmia has been described in neurological disorders, including temporal epilepsy. We reported a case of parosmia associated with unilateral hyposmia and mesial temporal sclerosis. We assessed the olfactory function by using Sniffin' sticks test and olfactory event-related potentials (OERPs). The findings of unilateral deficit of identification associated with parosmia only in the side ipsilateral to mesial temporal sclerosis area, that involves temporal olfactory regions responsible for higher level of smell processing, suggest a central genesis of olfactory disorders. The administration of levetiracetam restored olfactory function, OERP N1-P2 amplitude, and mesial temporal sclerosis-related electroencephalographic findings.

The function of orthologues of the human Parkinson's disease gene LRRK2 across species: implications for disease modelling in preclinical research

In the period since LRRK2 (leucine-rich repeat kinase 2) was identified as a causal gene for late-onset autosomal dominant parkinsonism, a great deal of work has been aimed at understanding whether the LRRK2 protein might be a druggable target for Parkinson's disease (PD). As part of this effort, animal models have been developed to explore both the normal and the pathophysiological roles of LRRK2. However, LRRK2 is part of a wider family of proteins whose functions in different organisms remain poorly understood. In this review, we compare the information available on biochemical properties of LRRK2 homologues and orthologues from different species from invertebrates (e.g. Caenorhabditis elegans and Drosophila melanogaster) to mammals. We particularly discuss the mammalian LRRK2 homologue, LRRK1, and those species where there is only a single LRRK homologue, discussing examples where each of the LRRK family of proteins has distinct properties as well as those cases where there appear to be functional redundancy. We conclude that uncovering the function of LRRK2 orthologues will help to elucidate the key properties of human LRRK2 as well as to improve understanding of the suitability of different animal models for investigation of LRRK2-related PD.

Reliability and validity of the Chinese version of the questionnaire of olfactory disorders (QOD) when used with patients having olfactory dysfunction

To cross-culturally adapt the Questionnaire of olfactory disorders (QOD) into a Chinese version, and then evaluate its reliability and validity for testing patients with olfactory dysfunction. A Chinese version of the QOD was evaluated for test-retest reliability, split-half reliability, and internal consistency. The validity analysis included components of content validity and criterion-related validity, as well as comparisons between The Medical Outcomes Study's36-Item ShortForm Health Survey(SF-36)questionnaire and the WHO Quality of Life-BREF (WHOQOL-BREF)questionnaire. A total of 125 patients with olfactory dysfunction were tested, and 104 patients completed three different surveys (QOD, SF-36, and WHOQOL-BREF). The test-retest reliabilities of the QOD-Parosmia statements (QOD-P), QOD-Quality of life (QOD-QoL), and QOD-Visual simulation (QOD-VAS)sections were 0.802 (P < 0.001), 0.797 (P < 0.001), and 0.468 (P < 0.001), respectively, and the Cronbach's α coefficients of internal consistency were 0.473, 0.814, and 0.882, respectively. The split-half reliability was 0.70. No correlation was found between the QOD-P section and the SF-36; however, there were statistically significant correlations between the QOD-QoL andQOD-VAS sections and the SF-36. The same results were observed for correlations between the QOD and WHOQOL-BREF. The Chinese version of the QOD was proven to be a generally reliable and valid questionnaire for use in evaluating mainland Chinese patients suspected of having olfactory dysfunction. However, the QOD-P section requires further modifications to properly evaluate patients with a Chinese cultural background and type of cognition.

[Methods for evaluating of olfactory function in patients with Parkinson's disease]

Olfactory disorder takes a special place among non-motor symptoms of Parkinson's disease (PD) as one of earliest signs of the disease. Based on literature data, authors suggest that simple and structured tests for detection of olfactory disorders should be part of diagnostic algorithm for early detection of PD) and occupy a special place in differential diagnosis of diseases of the extrapyramidal system. Literature on the methods of study of olfactory function recommended as an additional instrument for PD diagnosis is presented.

A novel mitochondrially-targeted apocynin derivative prevents hyposmia and loss of motor function in the leucine-rich repeat kinase 2 (LRRK2(R1441G)) transgenic mouse model of Parkinson's disease

Recently, we demonstrated that dimeric apocynin prevented loss of motor function in the leucine-rich repeat kinase 2 (LRRK2(R1441G)) transgenic (tg) mouse (treated with 200mg/kg, three times per week) [B.P. Dranka et al., Neurosci. Lett. 549 (2013) 57-62]. Here we extend those studies by treating LRRK2(R1441G) mice with an orally-available, mitochondrially-targeted apocynin derivative. We hypothesized that the increased mitochondrial permeability of Mito-apocynin, due to the triphenylphosphonium moiety, would allow improvement of Parkinson's disease (PD) symptoms at lower doses than those required for diapocynin. Tests of motor coordination (pole test, Rotor-Rod) revealed a significant deficit in coordinated motor function in LRRK2(R1441G) mice by 15 months of age. Decreased performance on the pole test and Rotor-Rod in the LRRK2(R1441G) mice was prevented with Mito-apocynin treatment (3mg/kg, three times per week). Decreased olfactory function is an early indication of PD in human patients. LRRK2(R1441G) tg mice displayed deficits in sense of smell in both the hidden treat test, and a radial arm maze test. Interestingly, treatment with Mito-apocynin prevented this hyposmia, and animals retained normal ability to identify either a scented treat or a food pellet as well as wild type littermates. Together, these data demonstrate that the mitochondria-targeted apocynin analog is effective in preventing early PD-like symptoms in the LRRK2(R1441G) mouse model.