Hassoun developed a theory of depression and a reparative theory of transmission. He wrote about certain pathologies in children of immigrants. Hassoun examined the special problems they face in processing and transmitting what is mostly communicated to them through their parents' narratives of displacement, loss and exile. He was one of the first to evoke the heritage of the Jews of Egypt in modern times. He wrote about their history, customs, religious observance, and languages. He showed particular interest in the Karaite community.