What causes Down syndrome?

Medical experts have determined how Down syndrome occurs, as well as cell behavioural differences during fertilisation that result in the various Down syndrome characteristics, but why additional chromosome copies occur is largely still a mystery. Although all of chromosome 21 genes have been identified and catalogued, the nature of their function is not entirely clear.

No matter the type, characteristics are fairly similar, with mosaic types having fewer physical effects. The common denominator is that all individuals with Down syndrome have a critical portion of chromosome 21 present in either some or all of the bodily cells.

Predicting the occurrence of Down syndrome is thus complicated, but certain risk factors which have been noted as common things to watch for can make it easier to potentially detect Down syndrome earlier should it occur.

Studies have also indicated that there is no definitive causal link to environmental factors or the activities of either healthy (normal) parent before or during pregnancy. There is nothing a person physically does or doesn’t do that can result in the development of Down syndrome during the fertilisation process. A person cannot influence, nor prevent the occurrence of the additional chromosome copy.

An additional copy of chromosome 21 can originate from either parent, although it is more commonly traced back to the mother (about 5% of cases originate from the father’s sperm). Robertsonian translocation is the only form of the condition which can pass on any type of Down syndrome to a future child. Not every child born to a parent with translocation Down syndrome will inherit the condition, however.