Genetics and Parkinson disease

Parkinson’s disease is a chronic, progressive and degenerative disease which affects the nervous system. Over ten million people in the world suffer from Parkinson’s, and around 1% of that is over sixty years of age. While no established studies have been conducted for Parkinson’s, incidence rates suggest that the occurrence is between 1.5 to 20 people per 1,00,000 a year. Characterized by the shaking and slowness of the body, Parkinson’s disease occurs due to  deficiency   of the chemical ‘dopamine’  produced in  the part of the brain known as the ‘substantia nigra’, which is responsible for the smooth and coordinated muscle movements of the body.

Parkinson disease is the neurodegenerative disease characterized by tremors, bradykinesia, rigidity and postural instability. An English doctor James Parkinson gave the first description of patients of this disease and a French neurologist Jean Martin Charcot refined it further. Parkinson disease was not known is considered to be a synucleinopathy which occurs as a result of excessive and abnormal deposition of an alpha synuclein protein in the substantia nigra pars compacta leading to disruption of major circuits thus the motor manifestation of PD. Over Seven million people worldwide are suffering from this disease and most of these cases are sporadic. Out of seven million patients 80 % had late onset, after 60 years of age and 10-20 % of patients are diagnosed PD before 50 years of age. 

For decades scientists were unaware regarding the exact cause of deposition of alpha synuclein but in 1997 researchers of National Institute of Health discovered a mutation in SNCA gene which encodes for alpha synuclein. Thereafter further new genes were discovered that had strong association with PD. Patients having SCNA gene have rapidly progressive, early onset Parkinson disease and have atypical features with good response to drugs. The penetration of these gene are high. Second gene which showed a strong association with Parkinson disease is Parkin (PARK2).Many gene were detected which has confirmed association with Parkinson disease PARK gene detected till date are both autosomal dominant and recessive. Till date PARK 1to PARK 18 have been delineated. 

Genetic test for PD

Although, in the last few decades, many genetic mutation have been detected which were linked to Parkinson disease but all patients don’t require genetic testing for the same. The patients having atypical symptoms, early onset of disease and having family history of PD can undergo genetic mapping for its confirmation. In other patients genetic studies may be requested for prenatal testing. All genetic testing  should follow strict protocol with the involvement of genetic counselor pre and post the evaluation.

Advantages 

Genetic evaluation helps in better understanding the disease process as well as help the patients in making informed choices at an early stage of disease. Genetic studies also gives us important and conclusive information regarding the prognosis of patients 

Summary

To summarize Parkinson disease is mainly sporadic disease but both autosomal dominant and recessive genetic forms of PD do exist. These are rare but they help in better understanding the pathophysiology of disease. Due to advancement in science, genetic testing is widely available but one should follow the strict guidelines for genetic evaluation. Genetic testing helps in minimizing the patients workup and assist in family planning as well as optimizing the treatment plan. It also helps us to detect patients at early stages of disease. Early detection of disease will not help in changing the treatment modalities or prognosis of the PD. Probably with the advancement in research, newer gene modifying modalities may come to rescue these patients.

While Parkinson’s has no cure, it’s onset and progression is extremely slow and symptoms can be controlled with treatment which helps maintain the quality of life for the patient. One should always remain alert for any indication regarding the worsening of the condition and should carry out instructions as per the doctor’s orders and with the help of a physical therapist.

Dr. Rima Khanna

Guest Author Consultant, Neurology, Fortis Hospital, Shalimar Bagh