What are the causes of people with down syndrome to have similar facial features?

A chromosomal proble: Downs' syndrome is usually a chromosomal problem caused by abnormality of chromosome 21. Hence, the development of similar facial features --- eyes slanted, low set ears, broad, larger mouth with broad large tongue; coarse hands with an unusual crease in the palm; some form of mental retardation -- all are a result of the chromosomal problem. Many will have congenital heart disease as well.

Chromosome influence: The size and shape of the skull and facial features of Down syndrome patients is heavily influenced by the effect of the extra chromosome present in every cell of the body.The same goes for eyes, hands, feet, all of which require a lot of decoding during formation to produce the structures.Other chromosome defects produce some common features to those born with a specified extra chromosome.