Yes, it is said to be based on some true elements. The story contains themes of family secrets and abuse which might have been inspired by real - life situations that the author was aware of.
Well, in 'Flowers in the Attic' book story, the kids are kind of imprisoned in the attic. Their mother has her own reasons which are slowly revealed as the story progresses. They endure isolation, hunger at times, and also deal with complex family dynamics. There's a lot of mystery and a sense of claustrophobia throughout the story.