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
A 2-month-old, breastfed baby that was normal at bih begins to develop GI problems and cirrhosis of the liver. Molecular analysis indicates a normal amount of galactose-1-phosphate uridyl transferase (GALT) mRNA, but no observable enzyme activity. Which of the following would be the best possible explanation for this? 
Select and explain. 
A. Gene deletion, B. Nonsense mutation, C. Premature transcription termination sequence in the DNA, D. Promoter mutation
B: Nonsense mutation
Answer: B: Nonsense mutation 
Explanation: Nonsense mutation