Patients Ask: Is Dementia Hereditary?

Is dementia hereditary? Many individuals with dementia and their family members express concern that they may pass down or inherit dementia, but the vast majority of dementias are not hereditary. In rare causes of dementia, such as familial Alzheimer’s disease, Huntington’s disease, and Familial Creutzfeldt-Jakob disease (CJD), there may be strong genetic links. However, such dementias account for a small fraction of dementia cases.

Below, we detail the hereditary nature of dementias with genetic influences and other factors for developing dementia.

When is Dementia Hereditary?

While inheriting dementia is rare, there are particular causes of dementia that have strong genetic influences. Let’s take a look into the hereditary nature of several dementias, including Alzheimer’s disease, Huntington’s disease, and Creutzfeldt-Jakob disease.

Alzheimer’s Disease

Researchers have found that there are specific genes and genetic mutations linked to each type of Alzheimer’s, though the presence of a genetic mutation does not necessarily indicate that an individual will develop Alzheimer’s disease. Alzheimer’s is typically categorized into two types:

1. Early-onset Alzheimer’s disease: Early-onset Alzheimer’s disease, or young-onset Alzheimer’s disease, is less common, accounting for less than 10% of Alzheimer’s cases, and refers to individuals under 65 who develop Alzheimer’s.
2. Late-onset Alzheimer’s disease: Late-onset Alzheimer’s disease is the most common form of Alzheimer’s and refers to individuals 65 and older who develop the disease.

Familial early-onset Alzheimer’s disease accounts for less than 1% of all cases of Alzheimer’s and is known to be linked to genetics. Research has revealed that inherited genetic mutations on three specific deterministic genes—amyloid precursor protein on chromosome 21, presenilin 1 on chromosome 14, and presenilin 2 on chromosome 1—can cause early-onset Alzheimer’s. Mutations in any of these three genes follow an autosomal dominant inheritance pattern, meaning that only a single copy of the defective gene will lead to the development of the disease. 

Risk genes for late-onset Alzheimer’s disease include genetic variants on the APOE gene on chromosome 19. The presence of one or two copies of APOE ε4 can indicate a higher risk of developing late-onset Alzheimer’s disease. However, it should be noted that genetics are not the only factor involved in the development of late-onset Alzheimer’s, meaning the presence of even two copies of APOE ε4 does not definitively indicate that an individual will develop Alzheimer’s.

Huntington’s Disease

Huntington’s disease is a rare autosomal dominant disorder that is caused by an inherited defect in a single gene. In particular, Huntington’s disease is the result of a mutation of the Huntingtin (HTT) gene on chromosome 4. The disease induces progressive degeneration of nerve cells in the brain and causes changes in the central area of the brain, resulting in a wide range of cognitive and functional impairments.

Familial Creutzfeldt-Jakob Disease

CJD is a prion disease that causes a type of dementia that progresses abnormally fast. It is generally categorized into three types:

1. Sporadic CJD accounts for approximately 85% of cases and develops spontaneously for no known reason.
2. Familial CJD accounts for roughly 15% of cases and is inherited in an autosomal dominant pattern.
3. Acquired CJR is rare, accounting for roughly 1% of all cases, and can be acquired through outside sources, such as medical procedures and meat or other cattle products infected with bovine encephalopathy.

While sporadic CJR and acquired CJR do not have any hereditary influences, familial CJR is caused by a mutation on the prion protein gene. The mutation causes the normal prion protein to change into the infectious form, which then continues to reproduce, causing severe dementia.

Other Factors Involved in Developing Dementia

Many causes of dementia are caused by environmental and lifestyle risk factors. While age is an obvious risk factor, other contributing factors include smoking, alcohol usage, insufficient physical activity, poor diet, a lack of mental and social engagement, and poor sleep. While many causes of dementia do not have direct hereditary influences, underlying risk factors that have hereditary influences may be at play. For example, a parent may pass down particular genes that increase the risk of high blood pressure, diabetes, and heart disease and may contribute to developing vascular dementia.

It is particularly important for all aging individuals, including those with risk factors, to regularly assess their neurocognitive health to understand when and if changes are occurring. Regular assessments of neurocognitive health are critical for those diagnosed with dementia to inform proper patient care and treatment.