Although we know Alzheimer’s disease involves progressive brain cell malfunction, we have not yet identified any single reason why these cells fail.

1) What is the approximate h² (value of heritability) of Alzheimer’s disease?

There is no official known cause of Alzheimer’s disease but many hypotheses are being based on research done in the past ten years. Especially twin studies have shown that the disease is most likely highly heritable:

In 2006, a study was done to determine patterns of Alzheimer’s in twins. They found it was more common for identical twins to both have Alzheimer's compared to non-identical twins. The researchers used a statistical analysis of risk rates within the groups in order to establish an estimate of how significant genetic factors are. They estimated heritability for Alzheimer's to be between 58% and 79%. Also, there was an average of 3.66 years difference in age at onset of the disease between 25 sets of identical twins, and 8.12 years difference between 20 sets of fraternal twins. This data suggests that genes had a role in determining when Alzheimer's was seen. *

At this time, only one gene, apolipoprotein E (ApoE) has been positively linked to late-onset Alzheimer's disease. However, only a small percentage of people carry the form of ApoE that increases the risk of Alzheimer's. Other genes or combinations of genes may be involved that we are still unaware of.**

Other research has shown that those who have a parent, brother or sister, or child with Alzheimer’s are more likely to develop Alzheimer’s. Also, the risk has been shown to increase if more than one family member has the illness. When diseases are likely to run in families, either heredity or environmental factors or both may play a role; but as stated above with Alzheimer’s disease this yet to be determined. ***

2) What environmental factor(s) influence Alzheimer’s disease?

Researchers have also explored several environmental factors that may play a role in Alzheimer’s disease or that activate the disease process in people who have a genetic vulnerability. Some studies have suggested a connection between severe head injuries in early adulthood and Alzheimer’s development. Lower educational level, which may decrease mental and activity and neuron stimulation, has also been investigated as an environmental factor. Although it has been hypothesized that infections, metals, or industrial toxins may trigger oxidation, inflammation and the disease process, thus far, there does not appear to be any conclusive evidence, that they cause Alzheimer’s disease.**

Thought to be risk factors that we can influence:

Head injuries: There appears to be a strong correlation between serious head injury and future risk of Alzheimer’s. Protect your head by buckling your seat belt, wearing your helmet when participating in sports.

Heart-head connection: There is strong evidence that links brain health to heart health. Every heartbeat pumps about 20 to 25 percent of your blood to your head, where brain cells use at least 20 percent of the food and oxygen your blood carries. The danger of developing Alzheimer’s or vascular dementia seems to increase with many conditions that damage the heart or blood vessels. These conditions include high blood pressure, heart disease, stroke, diabetes and high cholesterol. Work with your doctor to monitor your heart health and treat any problems that may occur.

General healthy aging: Other evidence suggests that strategies for overall healthy aging may help maintain a healthy brain and, in turn, even offer some defense against developing Alzheimer’s or related diseases. Try to keep your weight within recommended guidelines, avoid tobacco and excess alcohol, stay socially connected, and exercise both your body and mind***

sources referred to:

* http://news.bbc.co.uk/2/hi/health/4686806.stm and http://www.medpagetoday.com/Neurology/AlzheimersDisease/2633

** http://health.nytimes.com/health/guides/disease/alzheimers-disease/causes.html

***www.alz.org