This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
[{'content': 'A 16year old boy presents with symptoms similar to parkinsonism, on examination found to have dytonia and had no abnormalities on FD-PET scan, had clinical response to treatment with levodopa. What is the likely diagnosis? \nSelect and explain. \nA. Dementia with lewy bodies, B. Atypical parkinsomism, C. Dopa-responsive dystonia, D. Multiple system atrophy - parkinsonism type', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Parkinsonism can also be seen in Dopa-Responsive Dystonia, a condition that results from a mutation in the GTP-Cyclohydrolase 1 gene which can lead to a defect in a cofactor for tyrosine hydroxylase and the impaired manufacture of dopa and dopamine. While it typically presents as dystonia. it can present as a biochemically based form of parkinsonism (due to reduced synthesis of dopamine) which closely resembles PD and responds to levodopa, but is not associated with abnormalities on fluoro-dopa positron emission tomography (FD-PET) nor neurodegeneration. This diagnosis should be considered in individuals aged <20 years who present with a clinical picture resembling PD. Ref Harrison 20th edition page 3123', 'role': 'assistant'}]