This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Growth and development, Subject name: Pediatrics
The most common chromosomal syndrome is _____ 
Select and explain. 
A. Fragile-X-Syndrome, B. Trisomy 18, C. Trisomy 21, D. Trisomy 13
C: Trisomy 21
Answer: C: Trisomy 21 
Explanation: Trisomy 21 (Down&;s syndrome) is the most common chromosomal syndrome. Chromosomal disorders: These may involve autosomal or sex chromosomes. Involving autosomes Involving sex Chromosomes Down&;s syndrome (Trisomy 21) Edward syndrome (Trisomy 18) Patau syndrome (Trisomy 13) Cri du chat syndrome (5p deletion) Klinefelter syndrome (47,XXY) Turner syndrome (45,XO) Ref: Nelson textbook of pediatrics 21st edition Pgno: 659