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: Medicine
A 25 year old man presents with a kidney stone . He is married to his first Cousin and 6 months earlier , his 8 year - old son had a kidney stone as well diagnosis is . 
Select and explain. 
A. PCKD, B. Medullary Cystic disease, C. Fanconi syndrome, D. Cystinuria
D: Cystinuria
Answer: D: Cystinuria 
Explanation: Cystinuria  is the most common cause of stones in Childhood.