Severe brain loss that occurs before late adulthood could be caused by any of these factors except poor circulation genes senescence drug abuse

Severe brain loss that occurs before late adulthood could be caused by any of these except normal senescence. It is believed that before the age of 65, one percent of individuals experience significant brain loss. This condition may be caused by factors such as poor circulation of blood in the brain, genetic causes due to faulty genes and also drug and substance abuse that may impair brain functions. 

I’d go with d hope it