# Experimental Mis-Splicing Assessment and ACMG/AMP-Guided Classification of 47 ATM Splice-Site Variants

## TL;DR

This study experimentally assesses how 47 ATM gene splice-site variants affect RNA splicing and classifies them using clinical guidelines.

## Contribution

The study introduces splicing analysis of ATM variants using minigenes and integrates findings into ACMG/AMP guidelines for variant classification.

## Key findings

- 38 out of 47 ATM splice-site variants caused aberrant splicing.
- 30 variants resulted in negligible expression of full-length transcripts.
- Splicing assays improved classification of ATM variants as pathogenic or benign.

## Abstract

Pathogenic germline variants in the ATM gene are associated with a 20–30% lifetime risk of breast cancer. Crucially, a relevant fraction of loss-of-function variants in breast cancer susceptibility genes disrupts pre-mRNA splicing. We aimed to perform splicing analysis of ATM splice-site variants identified in the large-scale sequencing project BRIDGES (Breast Cancer After Diagnostic Gene Sequencing). To this end, we bioinformatically selected 47 splice-site variants across 17 exons that were genetically engineered into three minigenes and assayed in MCF-7 cells. Aberrant splicing was observed in 38 variants. Of these, 30 variants, including 7 missense, yielded no or negligible expression of the minigene full-length (mgFL) transcript. A total of 69 different transcripts were characterized, 48 of which harboured a premature termination codon. Some variants, such as c.2922-1G>A, generated complex patterns with up to 10 different transcripts. Alternative 3′ or 5′ splice-site usage was the predominant event. Integration of ATM minigene read-outs into the ACMG/AMP (American College of Medical Genetics and Genomics/Association for Molecular Pathology)-based specifications for the ATM gene enabled the classification of 30 ATM variants as pathogenic or likely pathogenic and 9 as likely benign. Overall, splicing assays provide key information for variant interpretation and the clinical management of patients.