Ultrasensitive techniques and protein misfolding amplification assays for biomarker-guided reconceptualization of Alzheimer's and other neurodegenerative diseases.

INTRODUCTION: The clinical validation and qualification of biomarkers reflecting the complex pathophysiology of neurodegenerative diseases (NDDs) is a fundamental challenge for current drug discovery and development and next-generation clinical practice. Novel ultrasensitive detection techniques and protein misfolding amplification assays hold the potential to optimize and accelerate this process. AREAS COVERED: Here we perform a PubMed-based state of the art review and perspective report on blood-based ultrasensitive detection techniques and protein misfolding amplification assays for biomarkers discovery and development in NDDs. EXPERT OPINION: Ultrasensitive assays represent innovative solutions for blood-based assessments during the entire Alzheimer's disease (AD) biological and clinical continuum, for contexts of use (COU) such as prediction, detection, early diagnosis, and prognosis of AD. Moreover, cerebrospinal fluid (CSF)-based misfolding amplification assays show encouraging performance in detecting α-synucleinopathies in prodromal or at-high-risk individuals and may serve as tools for patients' stratification by the presence of α-synuclein pathology. Further clinical research will help overcome current methodological limitations, also through exploring multiple accessible bodily matrices. Eventually, integrative longitudinal studies will support precise definitions for appropriate COU across NDDs.

Mitochondrial D-Loop Region Methylation and Copy Number in Peripheral Blood DNA of Parkinson's Disease Patients.

Altered mitochondrial DNA (mtDNA) methylation has been detected in several human pathologies, although little attention has been given to neurodegenerative diseases. Recently, altered methylation levels of the mitochondrial displacement loop (D-loop) region, which regulates mtDNA replication, were observed in peripheral blood cells of Alzheimer's disease and amyotrophic lateral sclerosis patients. However, nothing is yet known about D-loop region methylation levels in peripheral blood of Parkinson's disease (PD) patients. In the current study, we investigated D-loop methylation levels and mtDNA copy number in peripheral blood of 30 PD patients and 30 age- and sex-matched control subjects. DNA methylation analyses have been performed by means of methylation-sensitive high-resolution melting (MS-HRM) and pyrosequencing techniques, while mtDNA copy number was analyzed by quantitative PCR. MS-HRM and pyrosequencing analyses provided very similar D-loop methylation levels in PD patients and control subjects, and no differences between the two groups have been observed. Treatment with L-dopa and duration of the disease had no effect on D-loop methylation levels in PD patients. Additionally, mtDNA copy number did not differ between PD patients and control subjects. Current results suggest that D-loop methylation levels are not altered in peripheral blood of PD patients nor influenced by dopaminergic treatment.

Progress regarding the context-of-use of tau as biomarker of Alzheimer's disease and other neurodegenerative diseases.

Introduction: Tau protein misfolding and accumulation in toxic species is a critical pathophysiological process of Alzheimer's disease (AD) and other neurodegenerative disorders (NDDs). Tau biomarkers, namely cerebrospinal fluid (CSF) total-tau (t-tau), 181-phosphorylated tau (p-tau), and tau-PET tracers, have been recently embedded in the diagnostic criteria for AD. Nevertheless, the role of tau as a diagnostic and prognostic biomarker for other NDDs remains controversial.Areas covered: We performed a systematical PubMed-based review of the most recent advances in tau-related biomarkers for NDDs. We focused on papers published from 2015 to 2020 assessing the diagnostic or prognostic value of each biomarker.Expert opinion: The assessment of tau biomarkers in alternative easily accessible matrices, through the development of ultrasensitive techniques, represents the most significant perspective for AD-biomarker research. In NDDs, novel tau isoforms (e.g. p-tau217) or proteolytic fragments (e.g. N-terminal fragments) may represent candidate diagnostic and prognostic biomarkers and may help monitoring disease progression. Protein misfolding amplification assays, allowing the identification of different tau strains (e.g. 3 R- vs. 4 R-tau) in CSF, may constitute a breakthrough for the in vivo stratification of NDDs. Tau-PET may help tracking the spatial-temporal evolution of tau pathophysiology in AD but its application outside the AD-spectrum deserves further studies.

Is DAT imaging abnormality in normal pressure hydrocephalus always suggestive of degeneration?

Idiopathic normal pressure hydrocephalus (iNPH) is a debated entity with controversial pathogenesis, diagnostic criteria, and predictors of response after ventriculoperitoneal shunt (VPS). Parkinsonian signs are frequently reported in the clinical picture, sometimes due to the coexistence of an underlying neurodegenerative parkinsonism and sometimes in the absence thereof. To distinguish these two scenarios is crucial, since they may carry different long-term response to CSF drainage. 123I-FP-CIT-SPECT was believed to be helpful in this regard, however its role in predicting surgical outcome has been disputed. We illustrate a patient presented with gait disturbance, urinary incontinence, and asymmetrical parkinsonian signs, who underwent a 3T brain MRI and a 123I-FP-CIT-SPECT. VPS was performed. The patient repeated a 123I-FP-CIT-SPECT, 18 months after the operation, and was clinically followed up for 24 months. Our patient displayed clinical and radiological criteria for iNPH and an abnormal asymmetrical uptake in 123I-FP-CIT-SPECT, consistent with her asymmetrical parkinsonism. However, the organization of the substantia nigra studied with iron-sensitive sequences in 3T brain MRI scan appeared intact. The patient revealed an improvement both clinically and in 123I-FP-CIT-SPECT at postsurgical follow-up. Our report suggests that abnormal 123I-FP-CIT-SPECT may not necessarily reveal an overlap with neurodegenerative parkinsonism; its partial reversibility may suggest that the mechanical effect exerted on the striatum by ventriculomegaly ultimately leads to downregulation of dopaminergic transporters which may improve after VPS.

Quick Flicks: Association of Paroxysmal Kinesigenic Dyskinesia and Tics.

BACKGROUND: Paroxysmal kinesigenic dyskinesia (PKD) is a rare disorder characterised by brief attacks of chorea, dystonia, or mixed forms precipitated by sudden movement. METHODS: Observational study with a cohort of 14 PKD patients and genetic testing for PRRT2 mutations. RESULTS: In a series of 14 PKD patients seen in our clinic at the National Hospital of Neurology, Queen Square, from 2012-2017, we noted tics in 11 patients (79%), which stand in stark contrast to the estimated lifetime prevalence of tics estimated to reach 1%. CONCLUSIONS: The two reasons to point out this possible association are the clinical implications and the potential opportunity of a better understanding of shared pathophysiological mechanisms of neuronal hyperexcitability.

Aerobic rehabilitation program for improving muscle function in Parkinson's disease.

BACKGROUND: Parkinson's Disease (PD) is characterized by progressive and disabling symptoms. An impaired oxidative metabolism efficiency was supposed to be involved in the systemic impairment. Rehabilitative treatment represents a valid tool in promoting skeletal muscle's adaptations, even if no solid studies on muscle metabolic features are still available. OBJECTIVE: To evaluate the efficiency of skeletal muscle oxidative metabolism in PD patients in comparison with age-matched controls and test the role of an intensive aerobic treatment on muscle oxidative metabolism and its clinical effects. METHODS: 60 PD patients and 32 age-matched healthy controls participated. Haematic lactate values were detected during and after a submaximal incremental exercise on treadmill. The number of steps completed during the exercise was recorded. From these patients 10 underwent to an intensive aerobic treatment on treadmill (4 sessions/week for 4 weeks). Haematic lactate values and functional scales were recorded before (T0) and after (T1) treatment. RESULTS: At rest no significant difference in hematic lactate values between PD and control subjects was found. Lactate blood levels were significantly higher (p < 0,001) after the aerobic exercise test in PD patients compared to controls. These values remained higher at any time during recovery period (p < 0,001). No significant relationship between lactate values and the number of completed steps was found. After the rehabilitation treatment haematic value of lactate showed a significant reduction (p < 0,05) at 0, 5 and 10 minutes of recovery period with a normalization of value at 30'. All functional scales showed an improvement trend at T1, in particular Berg Balance Scale and 6 Meter Walking Test showed a significant reduction (p < 0,001 and p < 0,05 respectively). CONCLUSION: Our data clearly show an impaired muscle oxidative efficiency in PD subjects. The intensive rehabilitation program on treadmill showed a beneficial effect on muscle oxidative metabolism, endurance and balance, confirming the focal role of rehabilitation in PD patients.

Cervical Dystonia Following Injury to the Cerebellar Pontine Angle: An Instructive Case.

A 38-year-old woman presented with cervical dystonia in the context of a recent surgery to remove a vestibular schwannoma. She initially presented to neurology with pain in the right arm, and MRI of the brain showed an incidental right-sided vestibular schwannoma (Video 1, Segment 1). An elective gamma-knife procedure was performed, which failed. Hydrocephalus requiring ventriculoperitoneal shunt insertion developed, and 3 years following the initial procedure the lesion was surgically excised. Surgery was further complicated by right middle cerebellar peduncle injury, extending to the cerebellopontine angle and marginally to the right pontine tegmentum, with subsequent mass effect on cerebellum displayed on follow-up MRI (Video 1, Segment 2). Six months later, the patient experienced forced head deviation to the right, with difficulty moving from this position. Examination revealed clear right-sided torticollis, with hypertrophy of the left sternocleidomastoid muscle. Cervical dystonia worsened with action and nearly resolved with the patient lying down. A clear geste antagoniste, where symptoms improved with the patient touching the side of her head, was present (Video 1, Segment 3). Findings consistent with injury to the cerebellar pathways were additionally exhibited. She demonstrated clear dysarthria, bilateral dysmetria, dysdiadochokinesia (worse on the right), and prominent gait ataxia (Video 1, Segment 4). Although a possible role of the schwannoma itself in the cervical dystonia pathogenesis cannot be entirely ruled out, the timing of signs, occurring soon after the postsurgical injury, suggest a prominent involvement of structures lying within the cerebellar pontine angle.