Alzheimer's disease is associated with mutations in genes. Meaning that if one has a mother, brother, sister,etc, with Alzheimer's, one will most likely get it. The early-onset form of Alzheimer disease is inherited in a dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person inherits the altered gene from one affected parent.
One connection lies between a gene on chromosome 19, called the APOE gene, and late-onset Alzheimer's. That's the most common form of the disease that affects people over age 65.