It is rare for Parkinson's to run in families.
However, some gene variants have been strongly associated with Parkinson's particularly in people with a clear family history (with several other affected family members) or with a very early age at onset (when the condition developed). We all carry a large number of rare genetic variations, across 20 000 genes. The easiest way to pinpoint the variation relevant to Parkinson's is to compare family members with and without Parkinson's.
Read more about heritability and risk.