The other is the factor of heredity. The ratio of incidence between boys and girls is about five to one, and around 20 percent have a family history of language development retardation, inadequate intelligence or learning disabilities.
另一個則是遺傳因素，自閉症的男女比例差異很大，約為五比一，而其中百分之廿具有語言發展遲緩、智能不足，或學習障礙的家庭病史。