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: Pathology
A couple has two children affected with tuberous selerosis. On detailed clinical and laboratory evaluation (including molecular studies) both parents are normal. Which one of the following explains the two affected children in this family? 
Select and explain. 
A. Non penetrance, B. Uniparental diasomy, C. Genomic imprinting, D. Germline mosaicism
D: Germline mosaicism
Answer: D: Germline mosaicism 
Explanation: . Germline mosaicism