A variant of del(20q), an isochromosome of the long arm with the loss of an interstitial part of 20q, ider(20q), has been reported in patients with myeloid diseases. About 40 cases with this rearrangement have been reported up to 2012.
Molecular cytogenetic and array techniques have been used for mapping of the deleted region on 20q. The proximal breakpoints are consistently located in the 20q11.21 band, and the distal breakpoints span from band 20q13.13 to band 20q13.33.