Sporadic incidence
Alzheimer's mostly affects older people over the age of 65 years. The common scenario is where one member of a family is affected with the disease late in life. This is known as sporadic incidence of Alzheimer's disease and does not run in families. Other members of a family are at no greater risk of developing the disease if an elderly relative is diagnosed with Alzheimer's.

Is it hereditary?
Although rare, Alzheimer's disease can occur in people in their 30's, 40's & 50's. This is referred to as Early Onset Dementia and accounts for less than 10% of all cases of Alzheimer's disease. Scientists believe Early Onset Dementia is genetically transferred across the generations of some families, or in other words, is hereditary. It is this variation of the disease (also called Familial Alzheimer's) which runs in families.

As an example, if one of your parents developed Alzheimer's disease in their 70's or later, you would have no greater chance of developing the disease than what is the normal incidence in the general community.

If however, if you have a parent or close relative who developed the disease while under 60 years of age, there is a greater chance of other family members developing the disease in their younger years as well.

In summary, Alzheimer's disease, in rare cases, can be hereditary. When it does run in families it affects mostly younger members of the family ie) those under the age of 65.