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 large 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 β-satellite probe, and a second signal in addition to that present at the primary centromere under low stringency with α-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.
|Number of pages||6|
|Journal||American Journal of Medical Genetics|
|Publication status||Published - 1993|
- Alzheimer disease
- chromosome 22
- double nucleolus organizer region
ASJC Scopus subject areas