Test for LRRK2 mutations in patients with Parkinson's disease.

LRRK2-associated Parkinson's disease is common enough to raise clinical questions such as which patients should be tested and what advice should be given. We discuss practical issues in the light of our experiences with real life Parkinson's disease patients. Neurologists should consider testing LRRK2 in Parkinson's disease patients with affected first degree relatives where the onset is over the age of 40 years. A common G2019S mutation makes genetic testing straightforward and cost-effective. Age-related or reduced genetic penetrance means that LRRK2 mutations are also found in sporadic Parkinson's disease patients; however, at present, there is little to support the widespread testing of these patients except in high-risk ethnic groups such as North African Arabs and Ashkenazi Jews. Incomplete penetrance also complicates presymptomatic testing, which is best undertaken in the context of appropriate genetic counselling.