This study, published in the European Journal of Pediatrics (2026), focuses on identifying new genetic mutations responsible for Coffin–Siris Syndrome (CSS), a rare neurodevelopmental disorder.
Below is a summary based on the study’s abstract and results:
Background
Coffin–Siris Syndrome is characterized by developmental delays, intellectual disabilities, and distinct physical features (such as “coarse” facial features and small or absent fifth fingernails/toenails). It is primarily caused by mutations in the BAF chromatin-remodeling complex, with the ARID1B gene being the most common culprit.
Study Objective
The researchers aimed to identify novel pathogenic (disease-causing) variants in the ARID1B gene among patients clinically diagnosed with CSS and to evaluate how these mutations affect the patients.
Methodology
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Participants: Eight patients with a clinical diagnosis of CSS were enrolled.
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Testing: Whole Exome Sequencing (WES) was performed to look for genetic mutations.
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Analysis: The team used Sanger sequencing to confirm mutations in both the patients and their parents (trio analysis) and applied ACMG (American College of Medical Genetics and Genomics) guidelines to classify the severity of the variants.
Key Results
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Identification of Mutations: Genetic variants were identified in six out of the eight patients.
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Novel Findings: Out of the six variants found, five were previously unreported (novel). These included:
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Four nonsense variants (mutations that create a premature “stop” signal in the DNA).
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Two frameshift variants (mutations that delete or insert DNA bases, shifting the reading frame).
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Pathogenicity: All five novel variants were confirmed to be de novo (occurring for the first time in the patient, not inherited from parents). They all received high CADD scores (a tool used to predict the harmfulness of a mutation) and were classified as pathogenic under ACMG guidelines.
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Clinical Observations: Patients showed classic CSS symptoms, such as intellectual disability and growth delays. Some patients also showed slightly elevated blood ammonia levels and IGF-1 levels, though most other biochemical tests were normal.
Conclusion
The study successfully expanded the known genetic spectrum of Coffin–Siris Syndrome by identifying five new pathogenic mutations in the ARID1B gene. These findings reinforce that ARID1B haploinsufficiency (where one of the two copies of the gene is non-functional) is a definitive cause of CSS and provides valuable data for future clinical diagnoses.