Trisomy 21, also named Down syndrome was the most frequent autosomal aneuploidy and the most common cause of mental retardation. Fifty percent patients had congenital heart malformation. Every 20 minutes one case of trisomy 21 was born, and the incidence Trisomy 21, also named Down syndrome was the most frequent autosomal aneuploidy and the most common cause of mental retardation. Fifty percent patients had congenital heart malformation. Every 20 minutes one case of trisomy 21 was born, and the incidence