A Parkinson’s diagnosis tends to bring the worry along with it: “does this mean my children or my siblings will get it too?” The short answer is that in most cases the chance of it being passed on is not high enough to worry about.
Most of it is not inherited
For about 90% of people with Parkinson’s, the condition is idiopathic — no gene variant known so far is involved. Only the remaining 10% or so is understood to be linked to specific gene variants such as LRRK2, GBA or SNCAThe three best-known genes linked to Parkinson's. LRRK2 and SNCA can cause the condition when inherited from just one parent, and where a GBA variant is present, decline in thinking tends to progress relatively faster.Learn more (for a fuller explanation of the genes involved, see why Parkinson’s happens).
How much does a family history raise the risk?
The lifetime risk of developing Parkinson’s for the general population is about 1%. If a close relative such as a parent or sibling has Parkinson’s, that risk is reported to rise to around 2%. It is true that this doubles the risk, but in absolute terms it is still low — having a family history does not mean you will definitely develop Parkinson’s.
Carrying the gene does not mean you will develop it
Genes like LRRK2 can be passed on with just one copy of the variant (autosomal dominantA pattern of inheritance in which the condition can develop even if the variant gene comes from only one parent. LRRK2 and others are inherited this way.Learn more), but inheriting the variant does not mean a 100% chance of developing the condition. This is called incomplete penetranceIt means that inheriting a particular gene variant does not necessarily mean the condition will develop. Among family members carrying the same variant, some develop symptoms and others never do in their lifetime.Learn more. For example, the probability that someone with an LRRK2 variant actually experiences Parkinson’s symptoms varies with age: it is reported at about 28% by age 59, about 51% by 69, and about 74% by 79 — meaning the probability rises as you get older, but a fair number of people go their whole lives without symptoms. Genes like PRKNThe gene that makes the parkin protein. It is inherited in an autosomal recessive pattern and is known as one of the common genetic causes of early-onset (before age 50) Parkinson's disease.Learn more, by contrast, follow an autosomal recessiveA pattern of inheritance in which the variant gene must be inherited from both parents for the condition to develop. PRKN and others are associated with this pattern, and it is linked to early-onset Parkinson's disease.Learn more pattern, requiring the variant from both parents, and are associated with early-onset Parkinson’s diagnosed at a relatively young age.
The rates differ by ancestry and region
How often LRRK2- and GBA-related variants appear varies widely between populations. In Ashkenazi Jewish and North African Berber populations, for instance, a particular LRRK2 variant is reported to be common enough to be found in roughly 14% and 30% to 40% respectively of everyone with Parkinson’s — while in other populations it is far rarer. Differences like these also mean that the significance of a genetic test result can change depending on your own background.
Do you need a genetic test?
For most people, genetic testing isn’t necessary. It is worth considering in cases like these.
- Several people in the family have Parkinson’s
- You were diagnosed at a relatively young age
- You need to check eligibility for a clinical trial that targets a specific gene
Direct-to-consumer genetic test kits check only a limited set of variants, so their results can mislead. If you are considering testing, it is better to talk with a genetic counselor before and after, so you understand accurately what the result actually means.
What you can do now
If family history worries you, getting accurate risk information from your care team or a genetic counselor beats worrying vaguely about it. Having a gene variant does not mean you will definitely develop the condition, and conversely Parkinson’s can develop without one — genetics is only one cause among several.
This article is not a substitute for medical diagnosis or treatment. If you have questions about family history or genetic testing, please talk with your care team.
