Diagnosis and Testing
How do I get tested for familial Alzheimer Disease?
Not everyone is a good candidate for genetic testing for Alzheimer Disease. Molecular genetic testing is used in some cases of Familial Alzheimer Disease. Genetic testing is not required to assess whether Alzheimer Disease is familial or not, but it can help to fully confirm it. Analyzing the PSEN1, PSEN2, APP and APOE genes may provide you with more information on your risk to develop Alzheimer Disease. There are numerous genetic testing laboratories that offer testing for familial Alzheimer Disease. There are multiple types of tests to choose from. A genetic counselor can assist you as you decide what type of genetic testing is right for both you and your family. You can locate a genetic counselor at http://nsgc.org/p/cm/ld/fid=164.
More Diagnosis and Testing Content
Is there newborn testing for Alzheimer Disease?
As of June 2016, Alzheimer Disease is not on the newborn screen. It is unlikely Alzheimer Disease will be added to newborn screening unless a cure or effective treatment is found. In general, newborn screening only screens for childhood onset conditions.
Is there more than one genetic test for Alzheimer Disease?
There are many testing options for Alzheimer Disease. If there is a known mutation in a family, targeted testing can be ordered. With targeted testing, the laboratory will only look for one specific genetic change instead of checking the entire gene. This is generally the least expensive option offered by testing companies.
There are different test options for people with no known mutations in the family as well. Analyzing the PSEN1, PSEN2, APP and APOE genes may provide you with more information on your risk to develop Alzheimer Disease. The genetic testing approach will be influenced based on your personal medical and family history. There are benefits/ risks/ limitations to different types of genetic testing, and it is important to have genetic counseling from a qualified healthcare provider to aid in this decision making process.
Who else in my family should I test for familial Alzheimer Disease?
If you have a positive test result in a gene that can cause familial Alzheimer Disease, other family members may be at risk to have the same genetic change. First-degree relatives (siblings, children, and parents) may have a 50% chance to have the same genetic change. Second-degree relatives (nieces/nephews, aunts/uncles, grandparents, grandchildren, and half siblings) may have a 25% chance to have the same genetic change. Genetic testing is a personal decision. Not everyone at risk for a genetic condition chooses to have genetic testing. Some people will choose to proceed with the testing and some people will not. Each individual must consent to having genetic testing.
Does it matter if genetic testing is done on blood, saliva, or a biopsy sample for Alzheimer Disease?
Genetic testing for familial Alzheimer most often will be done on a blood sample. Some labs may allow for a saliva sample to be submitted, but this is not usually the preferred option for many labs. Solid tissue from a biopsy can also be used for testing, but a blood sample is generally the best option. You can find updated information on what sample a lab will accept at GeneTests.org.
What does a positive genetic test result mean for Alzheimer disease?
A positive genetic test result means different things depending on which gene was involved. If a genetic change was found in the PSEN1, PSEN2, or APP gene, this means there is a very high chance (95%-100%) that person will develop Early Onset Alzheimer disease (before age 65). This result may or may not change your medical management. Other relatives can be tested for the same genetic change to assess their risk for Alzheimer disease should they wish. If a genetic change was found in APOE showing you have either 1 or 2 e4 alleles, this increases your chance to develop Late Onset Alzheimer disease (over age 65) although there is no way to know for sure whether or not you will ever develop Alzheimer disease. Anyone with a positive Alzheimer disease genetic testing result is recommended to meet with a genetic counselor. To locate a genetic counselor near you visit www.nsgc.org.
What does a negative genetic test result mean for Alzheimer disease?
A negative genetic test result means that the laboratory analyzed the DNA and found no genetic changes that increase the risk for Familial Alzheimer disease. This result has different implications depending on who was tested.
- If your family has a known gene mutation and your testing results are negative then you are not at risk to develop Early Onset Alzheimer Disease.
- If your family does not have a known gene change (mutation), a negative result is less conclusive. This does not mean that the Alzheimer Disease in your family is not genetic. It just means we cannot identify the genetic change at this time. Anyone with a negative genetic testing result for Familial Alzheimer Disease is recommended to contact their healthcare provider yearly. It is possible in the future new genes are discovered and new genetic tests for Alzheimer Disease may be available.
Should children be tested for familial Alzheimer Disease?
It is not recommended to test minors for gene changes that cause Familial Alzheimer Disease. The youngest age at which a person can be tested is 18 years of age. Waiting until young adulthood to pursue genetic testing allows for the person to make an informed decision for himself or herself. Some people choose to be tested and some people choose not to be tested. It is important a person is able to make that decision for themselves.
What is the likelihood that someone has familial Alzheimer Disease?
Around 75% of the time, Alzheimer Disease is not inherited. The person diagnosed has no family history and no known genetic change that increases the risk for Alzheimer Disease.
25% of people with Alzheimer Disease have the Familial form. People with Familial Alzheimer Disease have a strong family history (more than 2 relatives affected) of Alzheimer Disease and/or in rare cases, a genetic change that increases the risk for Alzheimer Disease.
Is prenatal testing available for familial Alzheimer Disease?
Prenatal testing and preimplantation genetic diagnosis (PGD) is available for Familial Alzheimer Disease if the genetic change (mutation) present in the family is known. PGD allows for parents to only implant embryos into the mother’s uterus that do not have the genetic mutations that cause Familial Alzheimer Disease. PGD is still a very costly procedure, and it is not guaranteed to lead to pregnancy every time.
With prenatal diagnosis, the baby's DNA is tested during the pregnancy to determine whether the child has the gene mutation that causes Familial Alzheimer Disease. This can be done through a procedure called chorionic villi sampling (11-13 weeks of pregnancy) or amniocentesis (16-23 weeks of pregnancy). This practice is less commonly used for adult onset conditions like Familial Alzheimer Disease, especially if the genetic change only increases the risk slightly to develop Alzheimer Disease as an adult.
How can Alzheimer Disease be diagnosed without genetic testing?
A clinical diagnosis of Alzheimer Disease can be made from a patient’s symptoms. In 80-90% of cases, the diagnosis of Alzheimer Disease is correct. Signs of Alzheimer Disease include slowly progressive dementia and a brain MRI finding called gross cerebral cortical atrophy. Some people have a spinal tap done to check the levels of certain proteins in the cerebrospinal fluid which protects the brain and spinal cord. These proteins are called A-beta amyloid 42 and tau. The most accurate way to diagnose someone with Alzheimer Disease is to perform an autopsy after death. After a person with Alzheimer Disease passes away, their brain can be checked to look for amyloid plaques, tangles, and amyloid angiopathy which are abnormal findings in the brain. These findings prove the person had Alzheimer Disease.