Jan met all his developmental milestones appropriately in his first year. However, in his second year, he did not progress as expected. He did not use words, and even by age three, Jan was still grabbing his mother’s wrist to drag her over to the sink when he wanted juice instead of using a word to indicate what he needed. Furthermore, Jan showed no distress when his mother left him alone, and when he was at preschool, he did not engage with other children his age. He wriggled away from any attempt by his parents or grandparents to show him affection or to engage him in play. By age four, Jan would speak but would use the exact phrases he had heard from his favourite television programme, which was often inappropriate to the context and lacked any clear meaning. If the psychologist were to diagnose Jan’s abnormal behaviour according to the DSM-5-TR classification system, the diagnosis would most likely be - - - -