Supplementary Material for: CHAMP1-Related Neurodevelopmental Disorder: Two Turkish Cases with Novel Truncating Variants and Literature Review

Introduction: CHAMP1-related neurodevelopmental disorder (Neurodevelopmental disorder with hypotonia, impaired language, and dysmorphic features; MIM: 616579) (CHAMP1-NDD) is a rare autosomal-dominant condition caused by de novo truncating variants leading to haploinsufficiency. The phenotype is characterised by global developmental delay, intellectual disability, severe speech impairment, hypotonia, distinctive craniofacial features, and variable multisystem involvement. Case Presentation: We describe two unrelated girls harbouring novel de novo truncating CHAMP1 variants. Both presented with global developmental delay, profound speech impairment, hypotonia, postnatal growth impairment, and characteristic craniofacial features. Neuroimaging demonstrated normal findings in one patient and a thin corpus callosum in the other. Additional manifestations included high-grade vesicoureteral reflux in one individual and sensory dysregulation, reduced pain sensitivity, early-onset hyperphagia, and recurrent respiratory infections in the other. Perinatal complications were noted in one case; however, the overall phenotype was considered primarily attributable to the underlying genetic diagnosis. Exome sequencing identified heterozygous truncating variants, NM_032436.4:c.2081_2082del; p.Ser694* and NM_032436.4:c.2062dup; p.Glu688Glyfs*8, both confirmed as de novo and classified as likely pathogenic according to ACMG criteria. Conclusion: These cases expand the mutational spectrum of CHAMP1 and further delineate the phenotypic variability of this disorder, highlighting under-recognized systemic and behavioral features. Recognition of these additional clinical observations may facilitate earlier diagnosis and multidisciplinary management, although further studies in larger cohorts are required to clarify their clinical relevance.