Dementia, ALS, or Parkinson's in the family: when is it genetic?
When a parent or grandparent develops dementia, ALS, or Parkinson's disease, you may start to wonder: Is this going to happen to me?
For most families, the honest answer is reassuring. A single inherited gene does not cause most cases of these conditions. However, some are, and families where genetics plays a larger role often show patterns worth recognizing. Knowing the difference can change how you plan, how your family members think about their own health, and in some cases, what treatment or research options are available.
Not all cases are inherited
The role of genetics looks different for each condition:
Alzheimer's disease. Fewer than 1% of all Alzheimer's cases are caused by a single inherited gene. These families usually have Alzheimer's starting before age 65, often in their 40s or 50s, across more than one generation. You may also have heard of APOE, a common gene that raises or lowers Alzheimer's risk. APOE affects the odds, but it does not determine whether someone will develop the disease.
ALS. About 1 in 10 people with ALS has a known family history of it. The surprise is that a genetic cause also turns up in a meaningful share of people with no family history at all. In large population studies, a change in the C9orf72 gene shows up in roughly 1 in 4 to 1 in 3 people with familial ALS and in a smaller share of people with no known family history.
Parkinson's disease. For years, genetics was thought to explain only a small slice of Parkinson's. A large North American study called PD GENEration found that about 13% of participants had a genetic variant linked to their Parkinson's, most often in the GBA1 or LRRK2 genes. That rate was higher in people with early onset or a close relative with Parkinson's, but it was not zero in people without either.
So a family history is not destiny, and a lack of family history does not fully rule out a genetic cause. Both are reasons to look at the full picture rather than guess.
Family history patterns
Some patterns that can point toward a hereditary cause include:
Dementia, ALS, or Parkinson's that started before age 60 or 65
The same condition in two or more generations, especially on one side of the family
A mix of ALS and dementia in the same family, particularly frontotemporal dementia, which can share a genetic cause with ALS
Personality, behavior, or language changes in midlife that were labeled as psychiatric or "just stress" before a diagnosis was made
Involuntary movements, balance problems, or neuropathy that seem to run in the family
Ashkenazi Jewish, Basque, or North African Berber ancestry with Parkinson's in the family
A relative who already had genetic testing and was found to carry a variant
These are examples, not a complete list. Family history can also be incomplete or misunderstood for neurological conditions. A grandparent may have been described as "senile," or a diagnosis may never have been made. That uncertainty is a normal starting point for a genetic counseling conversation, not a barrier to having one.
Other neurological conditions with a genetic side
Dementia, ALS, and Parkinson's get the most attention, but genetics plays a role in many other neurological conditions. Examples include:
Huntington's disease, which causes changes in movement, mood, and thinking
Hereditary ataxias, which affect balance and coordination
Charcot-Marie-Tooth disease and other inherited neuropathies, which affect the nerves in the feet, legs, and hands
Some forms of epilepsy, especially when seizures start early in life or run in the family
Muscular dystrophies and other neuromuscular conditions
Some of these follow clear inheritance patterns, where each child of a person who carries the variant has a 50% chance of inheriting it. Others are more complex. Sorting out which pattern fits your family is one of the first things a genetic counselor will do.
Why testing for neurological conditions is different
There are two very different reasons someone might have genetic testing for a neurological condition.
Diagnostic testing is for a person who already has symptoms. The goal is to find the cause, which can confirm a diagnosis, guide care, and give the rest of the family clearer information.
Predictive testing is for a person without symptoms who wants to know their risk for developing the condition later on in life. For some conditions, that result can lead to earlier monitoring or treatment. For others, especially conditions where treatment options are still limited, a result can be a lot to carry emotionally and mentally. Some people find that knowing helps them plan and feel more in control. Others decide they would rather not know, or not yet. Both are valid choices.
There are practical considerations too. The Genetic Information Nondiscrimination Act (GINA) protects you from genetic discrimination in health insurance and most employment. It does not cover life, disability, or long-term care insurance. Some people choose to put those policies in place before predictive testing.
Because of all this, predictive testing for neurological conditions is best done with genetic counseling before and after the test, at a pace that feels right to you.
What a genetic answer can open up
For a long time, people asked why they should test for a condition that has no cure. There are a few reasons people may pursue neurogenetic testing:
Targeted treatment. In 2023, the FDA approved the first gene-targeted therapy for ALS, for people with ALS caused by a change in the SOD1 gene. Without genetic testing, those patients would not know they qualify.
Clinical trials. Several trials for Parkinson's are enrolling people with GBA1 or LRRK2 variants specifically, and research studies for inherited forms of Alzheimer's and ALS often look for people who know their genetic status.
Clearer diagnosis. For someone with symptoms, a genetic result can end years of uncertainty and point care in the right direction.
Planning. Some people use the information to make decisions about work, finances, family planning, or where they want to live.
Family clarity. Once a variant is found in one person, relatives can have a simple, targeted test if and when they choose. A negative result in a relative can be a real relief.
Not everyone will want every one of these. The point is to know your options so you can choose what fits your life.
How genetic counseling helps
A genetic counselor can help you sort out what your family history does and does not suggest, before you decide anything about testing. In a neurogenetics consultation, we can:
Build a detailed family history, including the gaps and the "we never really knew" diagnoses
Explain whether a hereditary cause seems likely and which condition or genes fit your family
Help you figure out who in the family is the best person to test first, which is often a relative who has symptoms
Talk through diagnostic or predictive testing, including the emotional, family, and insurance side, with no pressure either way
Choose and order the right test if you decide to move forward
Explain results in plain language and coordinate with your neurologist or other providers
If you already have results from a relative or from your own testing, a genetic test results review is a good place to start. Appointments are by video or phone, and no physician referral is needed.
If a neurological condition in your family has been on your mind, book a free discovery call. We can talk through your situation and whether a closer look would help.
Frequently asked questions
If my parent had Alzheimer's, will I get it?
Not necessarily. Having a parent with Alzheimer's raises risk somewhat, but most cases are not caused by a single inherited gene. Families with Alzheimer's starting before 65 in more than one generation are the ones where a hereditary form is more likely.
Should I get an APOE test?
APOE can increase the risk of developing Alzheimer's but does not guarantee whether you will develop it in your lifetime. Some people find the information useful, and others find it adds worry without changing what they do. It is worth talking through what you would do with the result before testing.
My relative with ALS or Parkinson's never had genetic testing. Is it too late?
Not always. Testing the affected person is usually the most informative step, so if they are living and willing, that is often the best place to start. If not, other family members may still have options, and a genetic counselor can help you figure out the best path.
