common chromosomal disorder World Health Organization Down syndrome 3000 to 5000 children born World Health Organization 3000 to 5000 children born estimated incidence 1 in every 1,000 babies According to the World Health Organisation 世界保健機関 World Health Organization estimated incidence World Health Organization estimated down syndrome World Health Organization estimated incidence estimated incidence estimated incidence Genes and chromosomal diseases: Down Syndrome 3000 to 5000 children born