# Assessment of X Chromosome Centromere Instability in Alzheimer’s Disease: A Quantitative FISH Approach

## TL;DR

This study uses a new quantitative FISH method to show increased X chromosome centromere instability in Alzheimer's disease brain tissue.

## Contribution

A novel quantitative FISH technique is introduced to assess X chromosome centromere instability in Alzheimer’s disease.

## Key findings

- AD patients showed a 7% average PCD frequency in X chromosome centromeres, compared to 3.2% in controls.
- The technique reliably distinguishes PCD+ and PCD− signals, indicating re-entered cell cycles and DNA replication.
- The method supports prior qualitative findings of chromosomal instability in Alzheimer’s disease neurons.

## Abstract

Chromosomal instability in Alzheimer’s disease (AD) neurons has been previously reported. This pilot study aimed to establish a quantitative technique for assessing X chromosome centromere signals using fluorescence in situ hybridization (FISH). Hippocampal brain tissue was collected at autopsy from sporadic AD patients and age- and gender-matched controls. FISH was utilized to detect and measure the intensity of hybridization signals for X chromosome centromeres in the interphase nuclei of hippocampal brain cells. The premature centromere division (PCD) phenomenon, marked by a close bipartite signal appearing as two separated FISH spots, was examined to see if the hybridized DNA amount in each spot matched the expected centromere DNA amount. The technique effectively distinguished between PCD+ and PCD− signals. The average PCD frequency of the X chromosome in the AD group was 7 ± 1%, compared with 3.2 ± 0.84% in the controls. This quantitative approach supports qualitative analyses of FISH centromere spots, reinforcing findings of chromosomal instability in AD. The presence of a double signal at the centromere of a single X chromosome indicates re-entered cell cycles, DNA replication, and PCD in hippocampal neurons. This technique provides a reliable method for identifying PCD + signals and contributes to understanding chromosomal instability in AD.