Supplementary Material for: A Novel Intragenic Duplication of CREBBP in Rubinstein-Taybi Syndrome: A Case Report Expanding the Genotype-Phenotype Spectrum

Abstract
Introduction: Rubinstein-Taybi syndrome (RSTS) is most often caused by loss-of-function variants in CREBBP; intragenic duplications are rare and extremely under-recognised.
Case Presentation: We describe a 5-year-old girl with global developmental delay, intellectual disability, frontal bossing, upslanted palpebral fissures, broad angulated halluces and scoliosis. Whole-exome sequencing with copy-number analysis revealed a heterozygous de novo duplication of approximately 13 kb encompassing exons 7–16 of CREBBP (NM_004380.3). Multiplex ligation-dependent probe amplification confirmed the duplication in the proband and excluded it in both parents. The event is predicted to introduce a frameshift leading to premature truncation. No additional pathogenic variants were detected.
Conclusion: This is the first reported CREBBP duplication spanning exons 7–16, expanding the mutational spectrum of RSTS and illustrating that intragenic duplications can manifest with a partially atypical craniofacial profile. The case underscores the value of incorporating high-resolution copy-number interrogation into RSTS workflows when single nucleotide variant analysis is uninformative and supports systematic deposition of such variants to refine genotype-phenotype correlations.