Psychiatric disorders mainly have a complex, multifactorial etiology. Apart from some infrequent exceptions (e.g., known genetic syndromes, fetal alcohol syndrome, congenital rubella), a single risk, whether genetic or environmental, is neither necessary nor sufficient to result in disorder. Thus, typical of all complex disease epidemiology, many carriers of risk CNVs will not display a psychiatric or neurodevelopmental phenotype, and not all those affected will possess the risk variant. As an analogy, although cigarette smoking is a well-established risk factor of large effect size, not all smokers develop lung cancer, and not all individuals with lung cancer have smoked. There are likely multiple types of risks and pathways that lead to the same child psychiatric disorder.
