title: A rare 6q11+ heteromorphism: cytogenetic analysis and in situ hybridization.
abstract: A rare variant of 6q11+ heteromorphism was found in a fetus and the mother during amniocentesis. The G- and Q-banding and DA/DAPI stain were negative. The C-banding was positive and the C-banded segment was 3-fold longer in the variant than in its homologue. Neither of the C-banded regions of chromosomes 6 decondensed when exposed to distamycin A or 5-azacytidine. A DNA replication study indicated that the C-banded variant was late replicating. The lateral asymmetry observed in the 6q11 variant after one replication cycle in 5-bromodeoxyuridine may result from an unequal interstrand distribution of thymidine in the repetitive DNA. Fluorescent in situ hybridization using a chromosome-6-specific alpha-satellite probe (D6Z1) demonstrated hybridization signals on the centromere of chromosome 6. The 6q11 variant showed a signal which was 3-fold larger than its homologue. These results indicate that the 6q11 variant is an amplification of a chromosome-6-specific alpha repeat, and the size of the hybridization signal correlates with the size of the laterally asymmetric and C-banded region.
authors.affiliation: Department of Pediatrics, Los Angeles County-University of Southern California Medical Center 90033.
authors.forename: M S
authors.initials: MS
authors.lastname: Lin
authors.forename: A
authors.initials: A
authors.lastname: Zhang
authors.forename: A
authors.initials: A
authors.lastname: Fujimoto
authors.forename: M G
authors.initials: MG
authors.lastname: Wilson
mesh_terms: D000649:Amniocentesis; D002871:Chromosome Banding; D002896:Chromosomes, Human, Pair 6; D005260:Female; D014644:Genetic Variation; D006801:Humans; D017403:In Situ Hybridization; D007621:Karyotyping; D011247:Pregnancy