Usefulness of α-synuclein as a Marker for Early Diagnosis of Parkinson's Disease in Skin Biopsy.

Overview

Parkinson's disease (PD) is a degenerative disease that can be difficult to diagnose. The clinicopathological studies had demonstrated a 76% accuracy in the clinical diagnosis of PD. At the beginning of PD is difficult for the clinician to distinguish from Parkinsonism Plus Syndromes (PPS) due to the similarity of symptoms and the lack of specific diagnostic tests. Specific biomarkers to help improve the accuracy of diagnosis and to separate these two entities are highly needed The histological hallmark for definite diagnosis of PD is the presence of fibrillar aggregates of phosphorylated alpha-synuclein called Lewy bodies (LBs) and Lewy neurites. Previous autopsy-based studies have revealed that alpha-synuclein is deposited in the peripheral autonomic nervous system including the enteric nervous system of the alimentary tract, cardiac plexus, adrenal medulla and skin. For this reason, in patients with parkinsonism, an alternative tool could be to demonstrate alpha-synuclein fibrillar aggregates in the skin, allowing early and appropriate diagnosis.

Parkinsonism, the syndrome, is a common movement disorder, and Parkinson's disease, the most common cause of parkinsonism, is the second most prevalent neurodegenerative disease after Alzheimer's disease. The clinical diagnosis of PD is based on the presence of the four common features: tremor when the limb is at rest, resistance to passive movement of the joints (rigidity), slowness and paucity of movement (bradykinesia and akinesia) and postural abnormalities. Approximately 25 percent of patients who received an initial clinical diagnosis of PD are found to have parkinsonism as part of another disorder, such as one of the so-called Parkinsonism-Plus Syndromes (PPS) The number and complexity of PPS seem to be increasing. This, along with the lack of diagnostic tests, makes it difficult for the clinician to distinguish between disease types. Some characteristic clinical features are used for the differential diagnosis, this manifestations include early and severe postural instability, falls in the first year of onset, abnormal eye movements, autonomic dysfunction, cerebellar signs and upper motor neuron signs. The PPS respond poorly to antiparkinsonian medications and have a worse prognosis than does PD. In spite of these suggestive features, not all PD patients have the same progression, in some cases it is impossible to separate typical PD from PPS, especially at the early stage. In this context, biological markers must be of great usefulness for the differential diagnosis of these entities. Some reports have described early features of PD such as (SPECT) imaging of the dopamine transporter that demonstrated the reduction of dopamine transporter in the striatum body at the early stage of PD and degeneration of the cardiac sympathetic nerve at the beginning of the disease process of PD; this occurs before neuronal cell loss is present in the dorsal vagal nucleus; This fact accounts for reduced cardiac uptake of meta-iodobenzylguanidine (MIBG), a physiological analog of norepinephrine. However, these diagnostic methods are not often performed. Therefore, more sensitive methods are needed to help improve the accuracy of diagnosis of PD.