Definition: Translocation Down syndrome occurs when two chromosomes, one of which must be a #21, join together at their ends. Instead of having three independent, separate number 21 chromosomes, a person with translocation Down syndrome has two independent #21 chromosomes and a #21 chromosome that is attached to another chromosome. The attached chromosomes are called a derivative chromosome and can occur for the first time in the person with translocation Down syndrome (de novo translocation), or the derivative chromosome can be inherited from a parent.
When a child is diagnosed with translocation Down syndrome, it is very important that the parents of the child also have karyotype testing to see if they carry this translocation.
While translocation Down syndrome occurs via a different mechanism, a child with translocation Down syndrome will have the same features and symptoms as a child with trisomy 21.
Translocation Down syndrome is one of the three forms of Down syndrome (the others are trisomy and moasicism). It accounts for 4 to 5% of Down syndrome cases.
Pronunciation: Trans low kay shun Down syndrome
Examples:
The karyotype test revealed that the infant had translocation Down syndrome due to a 14:21 chromosome translocation inherited from his father.
