Family with 22-derived marker chromosome and late-onset dementia of the Alzheimer type: II. Further cytogenetic analysis of the marker and characterization of the high-level repeat sequences using fluorescence in situ hybridization.
We have further characterized an unusual 22p+ marker chromosome with a double nucleolus organizer region (dNOR) previously identified in a family with late-onset dementia of the Alzheimer type. G-banding and morphology of the marker's q arm were typically normal. However, the p+ arm had a terminal cytological satellite and a GT-positive region at the midpoint. Standard C-banding documented 2 C-positive regions: one was associated with the primary centromere; the other, which was at the midpoint of the p arm, was not associated with a constriction. With replication-banding, there was a darkly staining region in the middle of the p+ arm that resembled the pericentromeric region of a chromosome 21 or 22. Fluorescence in situ hybridization with pXlr 101, a probe recognizing the full repeating unit of rDNA, indicated that the marker had an unusually larger rDNA region; with pU 1.2, a probe recognizing the human rDNA promoter, the signal was a doublet. The marker had 2 signals with a beta-satellite probe, and a second signal in addition to that present at the primary centromere under low stringency with alpha-satellite probes and a classic satellite probe. Immunostaining of chromosome spreads after R-banding and ultraviolet (UV) denaturation showed that the major portion of the marker's p arm was highly methylated.
Percy
M E
ME
Surrey Place Centre, Toronto, Canada.
Dearie
T G
TG
Jabs
E W
EW
Bauer
S J
SJ
Chodakowski
B
B
Somerville
M J
MJ
Lennox
A
A
McLachlan
D R
DR
Baldini
A
A
Miller
D A
DA
D000368:Aged; D000544:Alzheimer Disease / Q000235:genetics*; D002503:Centromere / Q000737:chemistry; D002871:Chromosome Banding / Q000379:methods; D002892:Chromosomes, Human, Pair 22; D004276:DNA, Satellite / Q000032:analysis; D005260:Female; D005819:Genetic Markers; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D009697:Nucleolus Organizer Region / Q000473:pathology*; D012335:RNA, Ribosomal / Q000032:analysis; D012091:Repetitive Sequences, Nucleic Acid; D013194:Staining and Labeling
D004276:DNA, Satellite; D005819:Genetic Markers; D012335:RNA, Ribosomal