Alzheimer's and Genetics

Dementia is a set of brain illnesses that damage a person's mental functioning, especially memory, thinking, and behavior. Alzheimer’s disease is a form of dementia. It is imperative that we understand the cause of Alzheimer’s disease for more effective and targeted treatments.

At least it is known that there is likely to be more than a single cause for Alzheimer’s and that it develops due to the biological processes in the brain. Research into Alzheimer’s cause has been enhanced by the discovery of genes associated with it. A person's genetic make up can directly influence the chances for the onset and development of Alzheimer's. A person's genes are inherited from their biological parents and passed along family lines to their biological children.

The so-called genetic risk factors are discussed below:

Family Links

There are two main types of Alzheimer's disease:

Familial Alzheimer's Disease (FAD). It is a very rare form of Alzheimer's disease, which runs in families. It is also known as Early Onset Alzheimer's or Younger Onset Alzheimer's.
Sporadic Alzheimer's Disease. It is the most common form of Alzheimer's Disease, but researchers are still trying to work out how this develops. It is also known as Late Onset Alzheimer's.

Click here to reserve Alzheimer's Tips eBook. Learn a program that teaches people how to provide quality care to individuals with Alzheimer's disease and memory loss

1. Familial Alzheimer's Disease (FAD) - Early Onset Alzheimer's

Familial Alzheimer's Disease (FAD) is a very rare form of Alzheimer’s, and runs in very few families. If a parent has a specific mutated gene, then any children they have, have a 50% chance of inheriting and developing the disease.

The presence of the specific mutated gene means that the persons will eventually develop Alzheimer’s disease, usually in their 40’s or 50’s.

This form of Alzheimer’s affects a very small number of people. The total known number of FAD cases worldwide is about 200 people.

All instances of FAD that have been studied so far have a much earlier onset, and as many as 50 percent of FAD cases are now known to be caused by defects in one or more of three genes located on three different chromosomes inside the person's cells:

Amyloid Precursor Protein (APP) Mutation: Some families have mutations in a gene called amyloid precursor protein (APP), which causes an abnormal form of the amyloid protein to be produced.
Presenilin 1 Mutation: Other families have mutations in a gene called presenilin 1, which causes an abnormal presenilin 1 protein to be produced.
Presenilin 2 Mutation: Presenilin 2 is a gene very similar to presenilin 1, and when this gene is mutated, it causes an abnormal presenilin 2 protein to be produced.

Any of these mutations are believed to cause FAD.

Furthermore, even if only one of these mutations is present, and it is present in only one of the two matching genes inherited from their parents, the person will still inevitably develop FAD. This type of genetic inheritance is known as autosomal dominant inheritance.

There is no evidence at this stage that any of these mutations play a major role in the far more common sporadic (i.e. late-onset) Alzheimer's.

Scientists are striving to reveal the normal function of Amyloid Precursor Protein (APP) and the presenilin proteins to determine how mutations of these genes cause the onset of FAD.

Next page >