So how does Alzheimer's disease progress? Does it happen suddenly? Or do changes in the brain accumulate over years until suddenly the symptoms become evident? Researchers don't yet know the timeline of progression for all forms of dementia, but new insights are beginning to emerge related to one type, autosomal dominant Alzheimer's disease.
A study published in the August 2012 issue of The New England Journal of Medicine describes the clinical and biomarker changes that are found over the course of inherited Alzheimer's disease, known as autosomal dominant Alzheimer's disease. According to the National Emergency Medicine Association, although this version of Alzheimer's disease is rare in the general population, each child that is part of a family that has a parent with this disease has a 50 percent chance of developing the disease. Otherwise, this form of the disease accounts for 5-10 percent of cases of Alzheimer's disease.
In the published study, researchers looked at data form 128 participants who had a parent who developed autosomal dominant Alzheimer's disease. These participants took part in baseline clinical and cognitive assessments, blood tests, cerebrospinal fluid tests and brain imaging. The researchers then calculated the estimated number of years in the future when each participant would first begin to show symptoms based on the participant's age at the start of the study and the parent's age when the symptoms of Alzheimer's disease began. The researchers also reviewed the baseline data using the timeline for the emergence of expected symptoms in order to develop a sequence of the functional changes that are associated from Alzheimer's disease.
The researchers found that concentrations of amyloid-beta in the cerebrospinal fluid seemed to decline approximately 25 years before the time when symptoms should begin. A positron-emission tomography (PET scan) detected deposits of amyloid-beta in the brain 15 years before symptoms were expected to begin. Furthermore, the researchers found at this time point an increased level of brain atrophy as well as increased concentrations of tau protein in the cerebrospinal fluid.
Ten years prior to the onset of expected symptoms, researchers found that the participants' brains had an abnormal decrease in metabolic rate. The participants also displayed impairment of their episodic memory, which involves remembering past events that have been experienced, such as times, places, associated emotions as well as other contextual knowledge.
At the five-year mark, other changes were seen. For instance, researchers -- who used the Mini-Mental State Examination and the Clinical Dementia Rating scale to assess participants -- detected global cognitive impairment in which many parts of the brain were under siege from the disease. The researchers found that the participants met the criteria for being diagnosed with dementia three years, on average, after the researchers had anticipated the onset of expected symptoms.
The researchers noted that their results need to be confirmed with the use of longitudinal research data. They also warned that their findings may not apply to people who have sporadic Alzheimer's disease, which is the most common form of the disease that accounts for 90-95 percent of cases.
Despite the researchers' caution, I'd suggest that this is important news for everyone - like me - who is worried about developing this disease. We often think of this as an old person's disease. For instance, my mom started showing signs of memory loss when she was in her late 70s and ended up being diagnosed with Alzheimer's disease when she was 81 years old. She died when she was 83. I would suggest that she started developing the factors for this disease when she was much younger. And while the maternal line of Mom's family has a history of dementia, I'd also suggest that Mom's lifestyle choices - especially smoking, which has been found to increase the risk of dementia by researchers - contributed to when she developed the disease. Therefore, if you have reached middle age, take time to really review your lifestyle and make changes now. That's because changes made now may help you delay or avoid Alzheimer's disease later in your life.
Primary Resources for This Sharepost:
Bateman. R. (2012). Clinical and biomarker changes in dominantly inherited Alzheimer's disease. The New England Journal of Medicine.
Cognitive Robotics Lab. (nd). Episodic memory. Vanderbilt University School of Engineering.
National Emergency Medicine Association. (2003). National Alzheimer's council.