<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 14-year-old Caucasian girl presents to the pediatrician for poor balance. She reports a 7-month history of frequent falls that has progressively worsened. She has fallen 3 times in the past week and feels like she cannot walk normally. She was born full-term and spent 2 days in the neonatal intensive care unit for respiratory distress. She has had an otherwise normal childhood. Her family history is notable for multiple cardiac deaths before the age of 60. Her mother had a posterior spinal fusion for kyphoscoliosis as an adolescent. On exam, the patient has 45 strength in her bilateral upper and lower extremities. She walks with a staggering gait. Pes cavus is appreciated bilaterally. Skin examination is normal. This patient has a condition that is caused by a trinucleotide repeat of which of the following nucleotides?? A: CAG, B: CGG, C: CTG, D: GAA, E: GAC,  <response>: This is a clinical vignette describing a 14-year-old girl with progressive loss of balance and coordination, weakness, and pes cavus. She has a family history of early cardiac deaths and maternal kyphoscoliosis. The question asks about the trinucleotide repeat expansion that causes her likely diagnosis. The clinical features described are classic for Friedreich ataxia, an autosomal recessive neurodegenerative disorder caused by expanded GAA trinucleotide repeats in the FXN gene. This leads to reduced production of the protein frataxin and impaired mitochondrial function. Key features are progressive ataxia, dysarthria, weakness, loss of proprioception, pes cavus, and cardiomyopathy. Therefore, the answer is GAA repeats.D: GAA 