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Yes, dementia can have a genetic component, but not all dementia is inherited.
Dementia is an umbrella term describing a group of symptoms associated with progressive impairment of cognitive functions. Alzheimer’s disease, vascular dementia, dementia with Lewy bodies and frontotemporal dementia (FTD) are some of the major types.
From a genetic perspective, dementia can broadly be classified into monogenic and multifactorial forms.
Monogenic or Single-Gene Dementia
In a small proportion of families, dementia develops due to a pathogenic variant (disease-causing genetic change) in a specific gene.
Early-onset familial Alzheimer’s disease is associated with pathogenic variants in three important genes:
APP: Amyloid precursor protein.
PSEN1: Presenilin 1.
PSEN2: Presenilin 2.
These genes are involved in amyloid-beta processing. Certain pathogenic variants can contribute to abnormal amyloid-beta accumulation in the brain.
Familial Alzheimer’s disease associated with these genes generally follows an autosomal dominant inheritance pattern. An individual carrying a heterozygous disease-causing variant has a 50% chance of passing it to each biological child.
Multifactorial or Polygenic Dementia
Most Alzheimer’s disease cases, particularly those developing after 65 years, are not caused by a single genetic mutation.
Instead, several factors contribute to disease susceptibility, including:
Increasing age.
Family history.
Genetic susceptibility.
Cardiovascular health.
Diabetes and hypertension.
Smoking and physical inactivity.
Environmental and lifestyle influences.One important susceptibility gene is APOE. Its ε4 allele is associated with an increased risk of Alzheimer’s disease, particularly when two copies are present.
However, carrying APOE ε4 does not mean that a person will definitely develop Alzheimer’s disease.
Can Dementia Develop Without a Family History?
Yes. Many individuals diagnosed with dementia have no known family history.
This is because most dementia cases are not caused by a single inherited genetic mutation. Age, vascular health, environmental influences and other biological factors also contribute.
When should genetic counselling be considered?Genetic counselling may be particularly useful when dementia develops at a young age, multiple family members are affected or the family history suggests an autosomal dominant inheritance pattern.
A genetic counsellor can assess the family history, construct a three-generation pedigree and discuss whether genetic testing is appropriate.
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