AN UNUSUAL G-NEGATIVE BAND WITHIN 1QH REGION A RARE VARIANT OR AN ABNORMALITY

Morphological variations due to heterochromatic DNA of the secondary c onstriction region (qh) of human chromosome 1 are considered normal. T he structural abnormalities involving or in association within the qh region have been difficult to characterize by routine cytogenetic meth ods and in turn have often gone undetected, In the past, the presence of a G-negative band within the qh region of chromosome 9 has been con sidered as a rare or unusual variant. Fortuitously, we were referred t wo cases where a G-negative band was embedded within the secondary con striction region of chromosome 1. Whole chromosome #1 specific paintin g probe, did hybridize to the band, Both patients have speech delay, U nfortunately, the parents were not available to confirm the mode of in heritance, nor could a definite conclusion be reached concerning its m orbidity. Nevertheless, we are tempted to hypothesize that this is an unusual variant where a G-negative band apparently became genetically inert when it was sandwiched between two blocks of heterochromatin. Si milar to a rare variant of chromosome 9 it could be found in the qh re gion of chromosome 16 as well, whose clinical consequences remain obsc ure.