Booklet - 2003

Is Dementia Inherited by Mrs. Katy Judd, Dementia Research Group

Is dementia inherited?

Rarely, although dementia can be inherited in an autosomal dominant way. Familial Alzheimer’s Disease, Familial Prion Disease and Familial ‘tauopathies’ (which includes frontotemporal lobar degeneration) affect a small number of families in the country.

Familial dementias are caused by a fault (mutation) in a gene. Genes are made of DNA and are found in the cell nucleus as 23 pairs of chromosomes, one half of the pair from each parent.

Inheritance
When diseases are inherited in a ‘dominant’ it means that only one faulty copy of the gene is needed to develop the disease (i.e. the good copy cannot compensate for the faulty copy). The risk of passing the faulty copy to children is 50% (1 in 2 chance) for each pregnancy. An affected parent could have all children affected, or all children unaffected.

Does it skip a generation?
There is usually a strong family history of the illness and you may know of cousins, aunts/uncles and grandparents who are affected. The disease may appear to skip a generation if a person with the faulty gene dies of another cause before the illness develops.

If I inherit the gene, will I get the disease?
Yes. If you have the faulty gene, the good copy on the other paired chromosome does not give protection from the disease. You will develop the disease if you live long enough.

Genetic counselling and testing
The medical team caring for your affected relative will ask about family history of similar illnesses. If they are concerned that the illness may be inherited, they can test for known mutations. Where tests are available, they are complicated to carry out and it can take months to get a result. The person’s next of kin would be included in the counselling and testing process. Specific consent is needed to process such blood samples.

If the precise mutation is not known researchers may be interested in identifying it, and will need DNA from several affected family members. Identifying a new mutation takes many, many months, possibly a year.

If the precise mutation affecting someone is known, it is possible to test the person’s adult children to see whether they have inherited it. If you are thinking about finding out whether you have inherited the faulty gene you will need to be referred to a genetics clinic by a GP or hospital consultant. It will be helpful to discuss this with the medical team caring for your affected relative first.

Mrs. Katy Judd, Dementia Research Group

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