CHARACTERIZATION OF 2 EXTREME VARIANTS INVOLVING THE SHORT ARM OF CHROMOSOME-22 - ARE THEY IDENTICAL

The heteromorphic nature of the short-arms of human acrocentric chromo somes is considered the norm without any dire consequences, We charact erized two highly unusual chromosome 22 variants with extremely enlarg ed short arms by routine and molecular cytogenetic techniques, Routine banding revealed that the two variants were not alike, Therefore, a c haracterization by fluorescent in situ hybridization (FISH) technique became warranted and revealed their remarkable differences, The first variant apparently had a tandem duplication of bands p11.2 --> p13, wh ile the second variant had a loss of the beta-satellite and ribosomal DNA regions with an apparent amplification of the satellite III region , The formation of these extremely enlarged regions can occur by a var iety of mechanisms whose clinical significance remains obscure.