<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 4-year-old girl presents to the office with her parents who are concerned about their daughter and slow, progressive changes in her behavior. The girl was born at 39 weeks gestation via spontaneous vaginal delivery. She is up to date on all vaccines and was meeting all developmental milestones until about 2 years ago. At one point she had a vocabulary of several words and now she verbalizes in grunts. She also flaps her hands in a repeated motion and has difficulty walking. Her parents have tried several home therapies to improve their daughters symptoms including restricted diets, hydrotherapy, and a variety of nutritional supplements. The vital signs include: heart rate 90min, respiratory rate 22min, blood pressure 11065 mm Hg, and temperature 36.9C 98.4F. On physical exam, she is well nourished and stares absently out the window. Her heart has a regular rate and rhythm and her lungs are clear to auscultation bilaterally. She has mild scoliosis. Which of the following is the most likely diagnosis?? A: Autistic spectrum disorder, B: Cerebral palsy, C: Phenylketonuria, D: Rett syndrome, E: Tourette syndrome,  <response>: Based on the description in the question stem, the 4-year-old girl had normal development until around 2 years old, when she started losing language skills, exhibiting repetitive hand movements, and having difficulty walking. This regression in development after a period of normal development points to a neurodevelopmental disorder. The specific details provided, including the female gender, regression after normal development, hand flapping, and scoliosis, are classic for Rett syndrome. Phenylketonuria would present much earlier in infancy. Autism spectrum disorder, cerebral palsy, and Tourette syndrome do not involve this kind of developmental regression after a period of normal development. Therefore, Rett syndrome is the most likely diagnosis.D: Rett syndrome 