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
[{'content': 'In a child with absent thumb, radial detion of wrist, bowing of forearm, which of the following investigation will not be useful? \nSelect and explain. \nA. Bone marrow examination, B. Karyotyping, C. Platelet count, D. 2D ECHO', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Absent thumb present in Fanconi anemia diagnosed by bone marrow In TAR syndrome diagnosed by platelets count Holt Oram syndrome diagnosed by 2D ECHO (Absent thumb and radius associated with ASD)', 'role': 'assistant'}]