A novel mutation in SMARCB1 associated with adult Coffin-Siris syndrome and meningioma

• First report of a germline SMARCB1 mutation (c.1091A>C, p.Lys364Thr) associated with both adult Coffin-Siris syndrome type 3 (CSS3) and meningioma, expanding the phenotypic spectrum of SMARCB1-related disorders. • The novel missense mutation may abnormally activate the MAPK signaling pathway, linking chromatin remodeling defects to tumor progression and neurodevelopmental phenotypes. • Whole-exome sequencing identified the mutation in two adult siblings with selective verbal learning difficulties and language delays, highlighting the adult presentation of CSS3. • The study underscores the importance of surveillance for tumor development in adult CSS3 patients with SMARCB1 mutations.