In some cases, dementia is heredity, but this is not always the case. While dementia is not always inherited, having family members with the disease does increase the risk of getting it.
The biggest factor on whether dementia is inherited is the exact type of disease causing the dementia. For instance, Alzheimer's disease is rarely inherited, but Huntington's disease is inherited more frequently. As people age, they also have an increase risk of developing dementia. With some diseases that cause dementia, people can be tested at an early age to see if they have the genetic factors that can lead to the disease.