Parkinson’s Disease

What Is Parkinson’s disease?

Parkinson’s disease (PD) is a progressive neurodegenerative disorder affecting approximately 2% of the population over 60 years of age. Onset before age 21 is referred to as juvenile-onset PD. If symptoms appear before the age of 50, the disease is referred to as early-onset PD. The disease is associated with a broad spectrum of motor and non-motor features. Characteristic pathology includes neuronal loss in specific areas of the substantia nigra of the midbrain and widespread intracellular protein α-synuclein accumulation. Primary motor symptoms include tremor, muscle rigidity, and bradykinesia.

Since the 1990s, researchers have identified several major gene variants that increase the risk of developing PD. There is now an abundance of scientific literature documenting the frequency of these variants in different populations and their effects on phenotype and clinical course.¹²³ 

Globally only 15% of patients report a family history of PD symptoms. The remaining 85% of PD cases are classified as sporadic.⁴ The incidence of any known causal PD mutation is rare, occurring in less than 2% of the PD population. The two most common mutated genes associated with familial PD are LRRK2 and PRKN and are reported at frequencies of 0.7% and 0.3% respectively in all people showing PD symptoms. ⁴

However, the distinction between genetic and sporadic PD is blurry. No single-gene mutation in PD has a 100% penetrance. Multiple genetic risk factors likely act in synergy to increase the risk of both familial and sporadic PD. Such genetic susceptibilities interact with aging and environmental factors to cause disease. ⁴