This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics And Genetic Disorders, Subject name: Pediatrics
Thirteen pair of Ribs can be seen in all of the following except: 
Select and explain. 
A. Down syndrome, B. Holt-Oram syndrome, C. Turner syndrome, D. Incontinentia pigmenti
A: Down syndrome
Answer: A: Down syndrome 
Explanation: a. Down syndrome(Ref: Pediatric Surgical Diagnosis pg 10, Ref: Nelson's 20/e p 610-615, Ghai 8/e p 637-639)Thirteen pairs of ribs may be seen in:* Aarskog syndrome* Turner syndrome* Holt-Oram syndrome* Alagille syndrome* Incontinentia pigmenti* Fetal akinesia deformation sequence* Idiopathic