This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The first gene therapy (somatic enzyme) was successfully done in - 
Select and explain. 
A. SCID, B. Phenylketonuria, C. Thalassemia, D. Cystic fibrosis
A: SCID
Answer: A: SCID 
Explanation: SCID was 1st disease that was successfully treated by gene therapy.