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Introduction

Parkinson disease (PD) is a progressive neurodegenerative disorder and the most common cause of parkinsonism (bradykinesia PLUS either tremor or rigidity).

Risk factors

  • Age:  Advancing age is the biggest risk; the average age at diagnosis is 60.  Early-onset PD (age <50) represents ~10% of patients and is more likely to be familial/genetic.
  • Genetics:  Having a first-degree relative with PD elevates risk by threefold.  Monogenic forms account for <10% of PD and include single-gene mutations with autosomal dominant inheritance like SNCA (encodes alpha-synuclein) and LRRK2 (most common mutation); genes with autosomal recessive inheritance include Parkin, PINK1, and DJ-1.
  • Gender:  Men have a higher risk (estrogen may have a protective effect).
  • Environmental factors:  Exposure to certain toxins (eg, herbicides, pesticides, solvents) may be a risk factor.  Severe or repetitive traumatic brain injury (eg, boxer Muhammad Ali) is associated with increased risk.

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