# Gene Expression Variability and the Prediction of Clinical Outcome in Chronic Lymphocytic Leukemia

## TL;DR

This paper explores how gene expression variability helps distinguish aggressive from non-aggressive chronic lymphocytic leukemia subtypes and suggests it should be studied alongside genetic factors.

## Contribution

The paper introduces gene expression variability as a novel approach to classify and understand clinical subtypes of chronic lymphocytic leukemia.

## Key findings

- The aggressive subtype of CLL shows higher gene expression variability across patients.
- Genes with higher variability in the aggressive subtype are linked to cell-cycle and inter-cellular communication.
- A relationship between gene expression, methylation, and variability is identified, explaining some inconsistencies in prior studies.

## Abstract

Chronic Lymphocytic Leukemia (CLL) presents two subtypes which have drastically different clinical outcomes. So far, these two subtypes are not associated to clear differences in gene expression profiles. Interestingly, recent results have highlighted important roles for heterogeneity, both at the genetic and at the epigenetic level in CLL progression.

We propose to use gene expression variability across patients to investigate differences between the two CLL subtypes. We find that the most aggressive type of this disease shows higher variability of gene expression across patients and we elaborate on this observation to produce a method that classifies patients into clinical subtypes. Finally, we find that, overall, genes that show higher variability in the aggressive subtype are related to cell-cycle development and inter-cellular communication, probably related to faster progression of this disease subtype. We also find a non-trivial relationship between expression, methylation and gene expression variability, which we consider as a possible mechanistic basis for the apparent lack of a clear correlation between expression and promoter methylation reported in the literature.

We propose that gene expression variability should be considered on par with genetic variability in studying the link between tumour heterogeneity and phenotypes such as aggressiveness and resistance to therapy in CLL. Moreover, we start to outline interesting but complex relationships between the genotype, epigenotype and phenotype of potential biological and clinical consequences.