Final answer:
A 20-month-old girl who has regressed in development could be experiencing a medical or psychological condition like autism, Rett syndrome, or the effects of severe neglect. A complete medical and social evaluation is essential to diagnosis and outline appropriate intervention. Conditions such as PWS should also be considered.
Step-by-step explanation:
A 20-month-old girl who previously had functional language and appropriate developmental milestones but now shows a loss of these abilities could potentially be experiencing a medical or psychological condition that requires further assessment. Given the description of lack of response to prompts, loss of motor skills like hand-wringing, previous ability to talk and play, and now being listless, several differential diagnoses could be considered. These could include conditions like autism spectrum disorder, regressive conditions such as Rett syndrome, or even the result of severe neglect as seen in environmental deprivation. These suggestions, however, are not exhaustive, and it is crucial for the child to undergo a comprehensive evaluation by a medical professional who can assess her physical and neurological health, as well as consider the importance of her social environment.
A thorough assessment would likely include careful observation of behavior; speech and language evaluation; and potentially, genetic screening to rule out conditions like PWS (Prader-Willi Syndrome) which is associated behavioral diagnostic criteria such as developmental delays and poor muscle tone early in life. Social factors, as seen in the case of Danielle, who suffered severe neglect, should also be evaluated as they can have profound effects on development. It is also possible that the girl could be experiencing a neurological condition that has led to a degenerative process, affecting her ability to communicate and interact with others.