Parkinson’s disease or PD is a neurodegenerative disease which means that nervous dysfunction is gradual and progressive. In other words, it develops slowly and gets worse over time, affecting approximately 5 million people throughout the world. It is one of the diseases involving extensive ongoing research in the diagnostic and therapeutic areas. Most PD patients only discover the condition once signs and symptoms, usually those affecting movement, become obvious and affect daily functioning to a level that they need to seek medical advice. However, there are methods to diagnose Parkinson’s disease in the early stages when a person has no signs or symptoms (asymptomatic) or when it is too mild to be evident either to the patient or doctor.
These diagnostic tests should be conducted routinely on patients who are possibly at risk, like those with a familial history. Screening, however, is not as simple as with other conditions as familial Parkinson’s disease accounts for only a small number of cases. Other risk factors like age, gender and environmental factors are too arbitrary to define known risk groups who should undergo routine screening. Most cases of PD are due to unknown cause without clearly identified risk factors.
What is the blood test for Parkinson’s disease?
There is no definitive blood test for Parkinson’s disease. Laboratory biomarkers that would normally be identified when testing the blood, other body fluids or tissue samples as is the case with scores of other medical conditions is not available. Instead the diagnosis totally depends upon the expert opinion and is identified by a clinical diagnosis based on medical history and neurological examination. The diagnosis must essentially be made at the onset of the disease when the chance of neuroprotective effect of the treatment is at its peak.
However, the disease is often misdiagnosed due to the overlapping symptoms resembling other neurological conditions such as Alzheimer’s disease, Dementia with lewy bodies, and drug induced parkinsonism. This mandates the need for identification of disease specific biomarkers precisely at the early stages, which can help the physicians to slow down the symptoms, if not cure the disease entirely.
It is crucial to highlight the importance of the fact that the neurodegenerative changes associated with parkinsonism start long before the physical appearance of symptoms. A blood test is carried out to look for the specific proteins that are produced by the dying brain cells in the body in response to fight off parkinsonism. When brain cells die, their contents are partially spilled back into the blood in the form of debris. The body generates antibodies as a defensive response to clear off the debris. The diagnostic blood test for parkinsonism aims to detect specific antibodies in the blood at early stages of disease progression even before the physical manifestation of symptoms.
In addition, scientists all over the world are in the process of researching the new biomarkers and associated blood tests to diagnose parkinsonism in susceptible individuals at early stages. Imaging techniques including MRI and CT do not show any clear identifiable features, which can conclusively indicate the disease and thus they leave room for doubt. However, it is known that post mortem examination of the brain of a PD patient shows paleness of the substantia nigra. This is a part of the brain rich in dopamine-producing neurons and the paleness may be visible with the naked eye. Microscopically there may be a noticeable loss of catecholaminergic neurons and Lewy bodies may be found in the remaining neurons.
Genetic Testing for Parkinson’s Disease
Although the most common forms of Parkinson’s disease are not related to inherited genetic abnormalities, it may still be useful for families with a history of PD. Five genetic mutations have been identified in familial Parkinson’s disease and more recently, a new genetic mutation VPS35, has also been discovered. In addition, mutations in a gene called SNCA which is responsible to encode synuclein has been observed in families having a higher prevalence of PD. This holds hope for identifying high risk family members and possibly undertaking preventative measures before the onset of the disease.
A molecular fingerprint of parkinson’s disease patient could also be made by analysing the expression level of one gene or gene product at a time through “gene chip technology”. The expression analysis of 22000 genes is done on a single glass slide and it is known as “microarray”. This gene chip analysis done over the blood of a PD patient is compared with normal subjects, which opens the scope for the identification of a set of signature genes along with their characteristic appearance in the patient of PD, which forms the molecular fingerprint of Parkinson’s disease. Various bioinformatics techniques are then used to transform this ‘molecular fingerprint’ into a simple diagnostic test. The test is later performed using PCR technology.
However only 10% of Parkinson’s disease patients have been known to have a genetic cause. Also, Some genetic abnormalities may not be inherited but rather acquired in life with advancing age or due to environmental factors. Early identification of this genetic damage may also help to identify a person who is more at risk of developing Parkinson’s disease and therefore the necessary steps may be taken at the outset.
Other tests to diagnose Parkinson’s disease
Other ancillary tests such as olfactory testing using olfactory probes is also done. Olfactory dysfunction is considered to be an important early feature and a diagnostic factor in PD patients. Deficit in the sense of smell often precede the development of other clinical motor symptoms by years and is essentially used to assess risk of development of PD in otherwise asymptomatic and susceptible individuals. Over 95% patients of PD present with significant olfactory loss.
In addition, imaging techniques such as MRI and dopamine-transporter single-photon emission computed tomography imaging are of great help to rule out and exclude the differential diagnosis.
The lack of clearly identifiable biomarkers and confirmed diagnostic methods should not discourage those who are apprehensive about developing Parkinson’s disease. Understanding the risk factors, reducing it and identifying the early signs and symptoms and seeking medical attention are all measures that one can undertake to prevent or slow the progression of Parkinson’s disease.