This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
All of the following immunodeficiency diseases are due to Chromosomal instability or defective repair of genes except 
Select and explain. 
A. Ataxia telangiectasia, B. Bloom syndrome, C. Seckel syndrome, D. Chediak - Hegashi syndrome
D: Chediak - Hegashi syndrome
Answer: D: Chediak - Hegashi syndrome 
Explanation: .