In Down syndrome : The extra chromosome content can arise thr | NeuroPsychiatry

In Down syndrome :

The extra chromosome content can arise through several different ways.

The most common cause (about 92–95% of cases) is a complete extra copy of chromosome 21, resulting in trisomy 21.

In 1.0 to 2.5% of cases, some of the cells in the body are normal and others have trisomy 21, known as mosaic Down syndrome.

The other common mechanisms that can give rise to Down syndrome include: a Robertsonian translocation, isochromosome, or ring chromosome. These contain additional material from chromosome 21 and occur in about 2.5% of cases.