It is apparent that Alzheimer’s disease is devastating. Witnessing grandparents unable to remember the name of their daughter or their grandchild is heartbreaking. Learning a father has gone missing only to find out he got lost three blocks from his house because he forgot where he was causes immense sadness. Watching a loved one’s mind deteriorate is difficult to handle. So what causes this disease of forgetfulness? Genetics, amyloid plaques and neurofibrillary tangles are the three known causes of Alzheimer’s disease. According to the Alzheimer’s Association, these are the only known causes of Alzheimer’s disease.
Plaques in the brain
Amyloid plaque is a term used to describe the heavy insoluble protein clumps that are deposited in a part of the brain known as the hippocampus, which plays a primary role in memory. These insoluble tangles cause permanent nerve damage in this region of the brain and, as a result, patients will have problems with their memory. These plaques are only found on autopsy, making research into Alzheimer’s disease extremely difficult.
Neurofibrillary tangles are twisted tangles that clog the brain. Neurons are the functioning units or cells in the brain, and signals are sent down the neurons. Microtubules, like train tracks, hold down the neurons and aid in the signal conduction across the neurons. The protein that comprises these microtubules is called tau and this protein becomes twisted, clogging the microtubules and preventing signals from being sent down the neurons. These tangles of tau protein are seen in Alzheimer’s patients and cause disruptions in the nervous system.
Genetic cause in the elderly
Alzheimer’s disease does have a genetic component involved. The most common gene that is linked to Alzheimer’s in the elderly is the APOE e4 allele on chromosome number 19. Although a blood test can detect this gene, it is still not possible to predict whether a person will develop Alzheimer’s disease. In fact, some people with one or two APOE e4 alleles never develop the disease while others who become diagnosed with Alzheimer’s disease don’t have any APOE e4 alleles. Yet it is still true that having this “Alzheimer’s gene” still increases the risk of having the disease.
Genetic causes of early onset
Although Alzheimer’s disease is mainly a disease of the elderly, there is an early onset subtype that affects adults in their 30s and 40s. About half of the people who have a parent with Alzheimer’s disease will likely inherit the gene responsible for early-onset Alzheimer’s disease. The three genes that are known to be responsible for early-onset Alzheimer’s disease are APP on chromosome 21, which is the same chromosome that results in Down syndrome (therefore there is a known link between Down syndrome and Alzheimer’s disease), PSEN-1 on chromosome 14, and PSEN-2 on chromosome 1.
Much more work to do
Although there are known causes of Alzheimer’s disease and medications to treat the symptoms, much work and research still needs to be done to fully understand this complicated form of dementia, including how to prevent and treat it.
To learn more about how to help people living with Alzheimer’s and their caregivers, read previous blogs in this series. If you know someone who is struggling with a mental health disorder, a behavioral problem or an addiction, the Dual Diagnosis Helpline can help any time 24/7.