The missing link: ARID1B non-truncating variants causing Coffin-Siris syndrome due to protein aggregation

Area of Science:

• Genetics
• Molecular Biology
• Developmental Biology

Background:

• ARID1B gene mutations are the primary cause of Coffin-Siris syndrome (CSS).
• Most known ARID1B variants are truncating, leading to mRNA degradation.
• Non-truncating ARID1B variants are often classified as variants of unknown significance due to limited experimental data.

Purpose of the Study:

• To investigate the pathogenic mechanisms of non-truncating ARID1B variants.
• To evaluate the impact of variants in the EHD2 and ARID domains on protein function.
• To correlate molecular findings with Coffin-Siris syndrome phenotypes.

Main Methods:

• Cell line overexpression assays to study protein behavior.
• In silico structural analysis to predict variant effects.
• Genome-wide transcriptome and methylation analysis in affected individuals.
• Quantitative western blot analysis to assess protein levels.

Main Results:

• Non-truncating ARID1B variants in EHD2 and ARID domains cause protein misfolding and aggregation (aggresomes).
• Variants lead to cytoplasmic and nuclear aggregates, indicating significant pathological effects.
• Transcriptome and methylation patterns in affected individuals align with ARID1B haploinsufficiency in CSS.
• Protein levels remain unaffected, suggesting aggregation as the primary pathogenic mechanism.

Conclusions:

• This study provides strong evidence for the pathogenicity of previously unclassified ARID1B non-truncating variants.
• The findings offer new approaches for the genetic diagnosis of Coffin-Siris syndrome.
• Re-evaluation of ARID1B variants will improve understanding and management of CSS.