This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Pathology
An example for gain of function mutation is? 
Select and explain. 
A. Osteogenesis imperfecta, B. Ehler danlos syndrome, C. Marfan syndrome, D. Huntington's disease
D: Huntington's disease
Answer: D: Huntington's disease 
Explanation: Ans. (d) Huntington's diseaseIn Huntington disease, the trinucleotide repeat mutation affecting the Huntington gene gives rise to an abnormal protein, called huntingtin, that is toxic to neurons causing neurologic deficit