You should consider reading more deeply than Wikipedia to be properly informed on a subject. There are a handful of very rare mutations that confer a high risk of getting it that we can detect. They are very rare. This isn't the same thing as being able to give a risk score if the DNA doesn't have all the rare mutations. But the science is there for those unlucky rare cases to say there is a high chance that a specific coding of DNA will result in Parkinson's.