The fundamental causes of Alzheimer’s disease are still unknown but researchers are pursuing many avenues of discovery to better understand the disease. The most common theories for what may cause Alzheimer’s include the amyloid and tau hypotheses. Abnormal deposits of these proteins clump together in the brain, forming plaques and tangles that interfere with normal brain function.
Early signs and symptoms of Alzheimer’s disease are short term memory loss, problems with reasoning, judgment and critical thinking skills. Because is it impossible to pin down a date of onset, it is often referred to as an “insidious onset.” Individuals with the disease and their caregivers will typically have several examples of events taking place that eventually became too difficult to ignore, leading to the eventual diagnosis of Alzheimer’s disease.
Dementia is a syndrome and has many causes including vascular disease, Parkinson’s disease, alcoholism, traumatic brain injury, vitamin deficiencies and more. Alzheimer’s disease is the most common cause of dementia. While everyone with Alzheimer’s has dementia, not everyone with dementia has Alzheimer’s.
Approximately 50 million people worldwide are living with Alzheimer’s disease with an estimated 5.8 million people with Alzheimer’s are in the United States. With the aging of the population worldwide and in the US, these numbers are expected to double or triple over the next 50 years.
More women are affected with Alzheimer’s disease; however women, in general, live longer than men so the population of women is much larger. Research has shown that when the data is controlled for age effects, women still appear to be more affected than males and it is not clear why.
The rates of dementia and Alzheimer’s disease are higher in African Americans in the United States than in Caucasians. The reasons for these disparities are still unclear; however, African Americans also have higher rates of cardiovascular diseases such hypertension and diabetes. Cardiovascular disease, particularly occurring in midlife, has been implicated in some studies as risk factors for dementia.
The earliest structural changes that can be seen on routine neuroimaging, such as an MRI, is shrinkage – also called atrophy – usually in the middle parts of the temporal lobes in the hippocampus. In a less common version of Alzheimer’s disease, there can be atrophy in posterior cortical areas of the brain including the parietal lobes. Abnormal protein accumulation occurs in other parts of the brain even before the atrophy is detectable.
Alzheimer’s disease is considered early-onset when an individual is diagnosed before age 65. Approximately 250,000 people in the U.S. are estimated to have early-onset Alzheimer’s. This includes rare forms of dementia known as frontotemporal degeneration. While some cases are likely due to genetic factors, others are sporadic like later onset Alzheimer’s.
The vast majority of Alzheimer’s disease cases are sporadic, meaning that there is no history in the family of someone having ever had Alzheimer’s or another dementia. However, some cases of Alzheimer’s disease are indeed “genetic” and classified as Familial Alzheimer’s Disease (FAD). A child whose biological mother or father carries a genetic mutation for early-onset Alzheimer’s has a 50 percent chance of inheriting that mutation. If the mutation is inherited, the child has a very strong probability of developing early-onset FAD.
Many early-onset Alzheimer’s cases are caused by any one of a number of different single-gene mutations on chromosomes 21, 14 and 1. Each of these mutations causes abnormal proteins to be formed. Mutations on chromosome 21 cause the formation of abnormal amyloid precursor protein (APP). A mutation on chromosome 14 causes abnormal presenilin 1 to be made, and a mutation on chromosome 1 leads to abnormal presenilin 2.
Alzheimer’s disease is often said to be a “family” disease. At some point, individuals who are diagnosed cannot live alone, resulting in a minimum of two people being affected with each case of the disease. As the disease progresses, the person affected will increasingly require more care as Alzheimer’s robs the person not only of function, but also of language and communication skills, thinking, reasoning and decision-making skills, and will eventually require total care. Caring for a person with Alzheimer’s is a job that no one “applies” for, so family members are not trained, and are unexperienced or unprepared for this role making them susceptible to physical and emotional exhaustion, depression and feeling a sense of hopeless and helplessness in the face of the growing demands of care.
Nearly everyone has been affected by Alzheimer’s disease in one way or another. This is due to the fact that the fastest growing segment of the population are individuals over the age of 85 and Alzheimer’s is highly correlated with advancing age. The more people living into old age, the higher the percentage of Alzheimer’s disease and related dementia.
Faculty investigators studying Alzheimer’s disease at IU School of Medicine have a strong and long-standing commitment to this research. The school is among the top six institutions for research funding from the National Institute on Aging, the primary Federal agency supporting and conducting Alzheimer’s disease research.
Beyond conducting leading-edge research in its own laboratories, IU School of Medicine is a valuable national resource that supports research on Alzheimer’s disease throughout the United States. The school provides critical expertise and infrastructure used by scientists at other institutions to discover how to prevent and effectively treat Alzheimer’s disease.