Table of Contents
Down syndrome is a condition in which extra genetic material causes delays in the way a child develops, and often leads to learning difficulties. It affects 1 in every 800 babies born.
Several research studies done in the past have shown that Down syndrome has four root causes:
Non-disjunction event
Trisomy 21 is caused by a meiotic non-disjunction event. In this case the child has three copies of every gene on chromosome 21. This is the most common cause because about 96% of Down’s syndrome cases, with 88 percent coming from the maternal gamete and 8 percent coming from the paternal gamete, are caused by this non-disjunction!Translocation
The extra material is due to a change called translocation. The long part of 21 is attached to another chromosome. The parent with the translocation is missing information on the short arm of 21, but this does not have apparent effects. Through normal disjunction during meiosis, gametes are produced with extra copies of the long arm of chromosome 21. This isn't so common cause of Down syndrome because it is the cause of two to three percent of the observed cases.Normal arrangement and trisomy - combined
The individual is a mosaic of normal chromosomal arrangements and trisomy 21. This can occur in one of two ways:- A non-disjunction event during an early cell division leads to a fraction of the cells with trisomy 21; or
- A Down syndrome embryo undergoes non-disjunction and some of the cells in the embryo revert back to the normal chromosomal arrangement.
This is the cause of one to two of the observed Down syndrome cases.
Duplication
Rarely, a region of the 21st chromosome will undergo a duplication event. This will lead to extra copies of some, but not all, of the genes on chromosome 21.
Continue reading after recommendations