About 5% of the Alzheimer’s population has the younger-onset form of the disease, which develops between the ages of 30 and 60.
The majority of those who develop it at a younger age have the most common form of the disease known as sporadic Alzheimer’s.
Researchers have not discovered why symptoms appear at an unusually young age, and genetic ties are unclear.
Two types of genes play a role in determining whether someone develops a disease. These types are risk genes and deterministic genes. Alzheimer’s genes have been found in both categories.
Risk genes increase the probability of developing Alzheimer’s disease; however, it does not guarantee it will happen. Several risk genes are associated with the disease, most notably a gene called apolipoprotein E-e4 (APOE-e4), which may be a factor in about 20% to 25% of Alzheimer’s cases.
We all inherit a copy of some form of APOE from each parent. Those who inherit APOE-e4 from one parent have an increased risk of Alzheimer’s, while those who inherit APOE-e4 from both parents have an even higher risk, but it is still not a certainty for developing the disease.
Those with deterministic genes, according to the Alzheimer’s Association, have a 95% chance of developing the disease.
There are variations within these genes, coding three proteins — amyloid precursor protein (APP), presenilin-1 (PS-1) and presenilin-2 (PS-2). When Alzheimer’s is caused by these deterministic variations, it is called autosomal dominant Alzheimer’s disease, or ADAD or more commonly, “familial Alzheimer’s disease.”
Deterministic gene variations in the disorder have been found only in a few hundred extended families worldwide, and true familiar Alzheimer’s accounts for less than 1% of cases.
Genetic testing is available for these gene variations, but must be carefully considered by the individual and his or her health care provider.
Mapping out the pros and cons of undergoing these tests; consultations with close friends and families and other health care professionals; and weighing future options are all things to think about when making the decision to be tested.
If someone with a high risk or with the familial gene for younger-onset Alzheimer’s is found, this information could have an impact on future health care, disability and life insurance, employment, as well as possibly cause great anxiety and depression. That person's future plans surrounding his or her family are affected, and life changes are inevitable.
On the other side of the individual knowing he or she tests positive for the familial gene; he or she is able to perhaps participate in clinical trials and initiate planning, i.e., securing a financial future, making legal decisions and choices about care; and having an open dialogue with loved ones regarding putting things in place to cope with the effects of the disease.
Plans to go forward with genetic testing should be thoroughly considered and discussed extensively with skilled genetic counselors. A genetic counselor can be found through the National Society of Genetic Counselors.