First report of Coffin-Siris Syndrome with SMARCB1 variant, normal intelligence and mild selective neuropsychological deficits: A case report and literature review.

Background: The SMARCB1 gene encodes a subunit of the BRG1-Associated Factor (BAF) complex, and mutations in this gene have been linked to Coffin-Siris Syndrome (CSS) type 3. CSS is characterized by a range of developmental disabilities, facial dysmorphic features, and feeding difficulties. There's been noted genotype-phenotype correlation in CSS, with cases involving SMARCB1 mutations often exhibiting more severe language impairment and intellectual disability. Method: We conducted a review of reported CSS type 3 cases and presented the first instance of CSS associated with a SMARCB1 variant wherein the patient exhibited normal intelligence and only mild selective neuropsychological deficits. The patient underwent evaluation for feeding challenges, growth delay, and dysmorphic features during their second year of life. Subsequently, CSS diagnosis was confirmed due to a de novo heterozygous c.568C > T (p.Arg190Trp) variant in the SMARCB1 gene. Due to learning difficulties, the patient underwent a comprehensive neuropsychological assessment, which was related to the retrospective reconstruction of her medical and developmental history. Results: The patient demonstrated normal intelligence and adaptive functioning, with specific deficits in arithmetic and selective difficulties in verbal learning and long-term memory. Feeding difficulties and language delay observed in early childhood showed significant improvement over time. Discussion: We discuss this case in relation to previously reported CSS type 3 cases, emphasizing neuropsychological aspects. It's evident that neuropsychological features of CSS can vary among affected individuals, highlighting the importance of personalized support and interventions tailored to specific cognitive and emotional needs by healthcare professionals. Our case suggests avenues for future research to identify specific modifiers of phenotypic expression to explain variability in intellect among patients and pinpoint potential targets for gene therapy.