<prompt> NOT a mutation in Downs syndromeMosaicismRobersonian translocationMaternal non disjunctionVNTRs  <response>: D VNTRs A Variable Number Tandem Repeat or VNTR is a location in a genome where a short nucleotide sequence is organized as a tandem repeat is associated with major psychiatric disorders. Trisomy 21 also known by the karyotype 47, XX21 for females and 47,XY,21 for males. The extra chromosome 21 material may also occur due to a Robertsonian translocation in 2-4 cases. In this situation, the long arm of chromosome 21 is attached to another chromosome, often chromosome 14. 