Natural History Study of Synucleinopathies

Overview

Synucleinopathies are a group of rare diseases associated with worsening neurological deficits and the abnormal accumulation of the protein α-synuclein in the nervous system. Onset is usually in late adulthood at age 50 or older. Usually, synucleinopathies present clinically with slowness of movement, coordination difficulties or mild cognitive impairment. Development of these features indicates that abnormal alpha-synuclein deposits have destroyed key areas of the brain involved in the control of movement or cognition. Patients with synucleinopathies and signs of CNS-deficits are frequently diagnosed with Parkinson disease (PD), dementia with Lewy bodies (DLB) or multiple system atrophy (MSA). However, accumulation of alpha-synuclein and death of nerve cells can also begin outside the brain in the autonomic nerves. In such cases, syncucleinopathies present first with symptoms of autonomic impairment (unexplained constipation, urinary difficulties, and sexual dysfunction). In rare cases, hypotension on standing (a disorder known as orthostatic hypotension) may be the only clinical finding. This "pre-motor" autonomic stage suggests that the disease process may not yet have spread to the brain. After a variable period of time, but usually within 5-years, most patients with abnormally low blood pressure on standing develop cognitive or motor abnormalities. This stepwise evolution indicates that the disease spreads from the body to the brain. Another indication of this spread is that acting out dreams (i.e., REM sleep behavior disorder, RBD) a problem that occurs when the lower part of the brain is affected, may also be the first noticeable sign of Parkinson disease. The purpose of this study is to document the clinical features and biological markers of patients with synucleinopathies and better understand how these disorders evolve over time. The study will involve following patients diagnosed with a synucleinopathy (PD/DLB and MSA) and those believed to be in the "pre-motor" stage (with isolated autonomic impairment and/or RBD). Through a careful series of follow-up visits to participating Centers, we will focus on finding biological clues that predict which patients will develop motor/cognitive problems and which ones have the resilience to keep the disease at bay preventing spread to the brain. We will also define the natural history of MSA - the most aggressive of the synucleinopathies.

α-synuclein is a small protein of 140 amino acids that is highly expressed in the brain. It's function remains poorly understood.10 Synucleinopathies are a group of neurodegenerative diseases associated with the abnormal accumulation of α-synuclein within cytoplasmic inclusions in neurons or oligodendroglia. These α-synuclein containing cytoplasmic aggregates occur throughout the brain, producing cell death and specific motor, autonomic and cognitive dysfunction in four phenotypically distinct synucleinopathies. When α-synuclein deposition occurs in neurons it aggregates into Lewy bodies, producing Parkinson disease (PD), dementia with Lewy bodies (DLB) or pure autonomic failure (PAF). Whereas in multiple system atrophy (MSA) neuronal death probably occurs as a consequence of α-synuclein aggregation in oligodendroglia. A characteristic feature of the synucleinopathies is that they can all begin with varying degrees of autonomic dysfunction as the sole clinical feature - implying an initial diagnosis of isolated (pure) autonomic failure 11. After a variable period of time, but usually less than 5 years, only a small number of patients remain with a pure autonomic failure phenotype, but careful follow-up is lacking 11. Most patients develop cognitive or motor abnormalities (or both) and the patient is then diagnosed with PD, DLB or MSA. This stepwise clinical progression suggests that the neurodegenerative process can in rare cases remain confined to autonomic neurons12, but more frequently spreads to affect additional areas of the central nervous system (CNS). This unique feature of the synucleinopathies poses diagnostic challenges and potential therapeutic opportunities. The challenges are first, to determine whether PAF is a distinct disease or is always a prodromal phase of PD, DLB or MSA and second, to discover biomarkers that predict spread to motor and cognitive neurons. Such biomarkers would allow testing of disease-modifying strategies to delay or stop the neurodegenerative process in the pre-motor or pre-dementia phase. Aim 2 will focus on defining the natural history of MSA, the most aggressive of the synucleinopathies. This prospective observational study will establish disease-specific milestones for use in future clinical trials. Obstacles to identifying biomarkers predicting further CNS involvement are that most medical centers only see patients with synucleinopathies when they already have developed motor and cognitive involvement, and that PAF and MSA are rare disorders. In this context the Autonomic Disorders Consortium (ADC) within the Rare Diseases Clinical Research Network (RDCRN) of the National Institutes of Health (NIH) was created with the objective of providing a better understanding of the variability, progression, and natural history of neurodegenerative synucleinopathies. Continuing this observational study, and increasing its power by including additional academic centers from the U.S., South America, and Europe, will allow us to define the natural history of these diseases and establish the sensitivity and specificity of the proposed biomarkers.