The study confirmed that diagnosis of newborns and control of blood phenylalanine concentration improves verbal intelligence and spoken language scores in phenylketonuria subjects.

↑What is "already known" in this topic: • Previous studies showed progress of language skills, communication, and speech abilities in English-speaking children with hearing impairment after cochlear implantation (CI). • There is no systematic review on Farsi-speaking children with CI. →What this article adds: • Cochlear implant surgery is an effective way for the development of language skills in Persian-speaking children, as well as English-speaking children. • Many other aspects of language such as pragmatics, semantics and several subcategories of grammar need to be studied in Persian speaking children with CI.