Molecular topography of the secondary constriction region (qh) of human chromosome 9 with an unusual euchromatic band
- State Univ. of New York Health Science Center, Brooklyn (United States)
Heterochromatin confined to pericentromeric (c) and secondary constriction (qh) regions plays a major role in morphological variation of chromosome 9, because of its size and affinity for pericentric inversion. Consequently, pairing at pachytene may lead to some disturbances between homologous chromosomes having such extreme variations and may result in abnormalities involving bands adjacent to the qh region. The authors encountered such a case, where a G-positive band has originated de nova, suggesting a maternal origin from the chromosome 9 that has had a complete pericentric inversion. In previously reported cases, the presence of an extra G-positive band within the 9qh region has been familial, and in the majority of those cases it was not associated with any clinical consequences. Therefore, this anomaly has been referred to as a [open quotes]rare[close quotes] variant. The qh region consists of a mixture of various tandemly repeated DNA sequences, and routine banding techniques have failed to characterize the origin of this extra genetic material. By the chromosome in situ suppression hybridization technique using whole chromosome paint, the probe annealed with the extra G-band, suggesting a euchromatic origin from chromosome 9, presumably band p12. By the fluorescence in situ hybridization technique using alpha- and beta-satellite probes, the dicentric nature was further revealed, supporting the concept of unequal crossing-over during maternal meiosis I, which could account for a duplication of the h region. The G-positive band most likely became genetically inert when it was sandwiched between two blocks of heterochromatin, resulting in a phenotypically normal child. Therefore, an earlier hypothesis, suggesting its origin from heterochromatin through so-called euchromatinization, is refuted here. If the proband's progeny inherit this chromosome, it shall be envisaged as a rare familial variant whose clinical consequences remain obscure. 52 refs., 3 figs.
- OSTI ID:
- 6281626
- Journal Information:
- American Journal of Human Genetics; (United States), Vol. 52:5; ISSN 0002-9297
- Country of Publication:
- United States
- Language:
- English
Similar Records
Cytogenetic and molecular characterization of a subtle familial 9q duplication in affected and normal individuals
Variants of chromosome 9 with additional euchromatic bands: Two case reports