Parkinson's Disease Genetics: What LRRK2 and GBA Variants Actually Mean for Your Risk
Two genes dominate the genetics of Parkinson's — and understanding penetrance is the difference between panic and perspective.
Most Parkinson's disease isn't inherited in a simple way — but two genes, LRRK2 and GBA, dominate what we do understand about its genetics. Carrying a variant in either raises risk without guaranteeing disease, and the concept that makes sense of that gap is penetrance.
Parkinson's disease is a progressive movement disorder driven by the loss of dopamine-producing brain cells. The overwhelming majority of cases are "sporadic" — arising from a tangle of genetic susceptibility, aging, and environment. But research has pinpointed genes that meaningfully shift the odds, and two matter most for the general public.
The two headline genes
GBA — the most common genetic risk factor
Variants in GBA are the most common genetic risk factor for Parkinson's identified so far. GBA is the same gene involved in Gaucher disease (a lysosomal storage disorder) when two copies are affected. Carrying a single GBA variant doesn't cause Gaucher disease but is associated with an increased Parkinson's risk. Crucially, the great majority of GBA variant carriers never develop Parkinson's.
LRRK2 — the most common autosomal-dominant cause
LRRK2 variants (the G2019S variant is the best known) are the most common single-gene cause of inherited Parkinson's. LRRK2-related Parkinson's is notable because it's a prime target for drugs in development. The G2019S variant is found more frequently in certain populations — including people of Ashkenazi Jewish and North African Berber ancestry — which is relevant context for interpreting a result.
Penetrance: the concept that prevents panic
This is the single most important idea in this article. Penetrance is the probability that someone carrying a variant actually develops the associated condition. For both LRRK2 and GBA, penetrance is incomplete — often substantially so. Many people carry these variants their entire lives and never develop Parkinson's. Risk is also age-dependent and modified by other genetic and environmental factors we don't fully understand yet.
Why some people still want to know
Predictive testing for a condition without a cure is deeply personal, and reasonable people choose differently. Reasons some people find value in knowing:
- Research participation. LRRK2 and GBA carriers are being actively recruited into studies and trials of targeted therapies — some of the most promising avenues in Parkinson's research.
- Baseline awareness. Knowing prompts attention to early, subtle signs and earlier neurological evaluation if symptoms appear.
- Family context. These variants run in families, and one person's result can inform relatives' decisions.
And reasons some people prefer not to know: there's currently no proven way to prevent Parkinson's, and a risk result can cause anxiety without a clear action. This is precisely why pre-test counseling matters for these particular genes.
Get the Data — Decide Later How to Use It
A whole genome sequence captures LRRK2, GBA and the broader genetic landscape. Because you keep the raw data, you can choose if and when to look at specific results — ideally alongside a genetic counselor for something as weighty as Parkinson's risk.
Get 10% Off Whole Genome Sequencing → Use code GENOME at checkout · Italian lab · Full 30x WGS · You keep the raw dataA note on responsible interpretation
Neurodegenerative-disease genetics is one of the areas where we most strongly encourage professional guidance before acting on a result. Ancestry affects how a variant should be interpreted, family history changes the picture, and the emotional weight of predictive results is real. A whole genome test gives you the data; a genetic counselor helps you decide what, if anything, it means for you.
This article is for general educational purposes only and is not medical advice. Genetic results should be interpreted with a qualified healthcare provider or genetic counselor. Do not start, stop, or change any medication or treatment based on this article.