DNA methylation signature and clinical delineation of PACS1-related disorder in 24 unreported individuals.

PACS1-related disorder (PACS1-RD), also known as Schuurs-Hoeijmakers syndrome, is a rare autosomal dominant neurodevelopmental disorder predominantly caused by the recurrent de novo c.607 C > T p.(Arg203Trp) gain-of-function variant. Although core clinical features have been delineated, systematic data on developmental milestones, growth parameters, and clinical variability remain limited. We assembled a series of 24 previously unreported, unrelated individuals with PACS1-RD and compared their clinical and molecular features with 84 individuals from the literature. Genome-wide DNA methylation profiling was performed on peripheral blood DNA using bisulfite sequencing, interrogating ~860,000 CpG sites. Our study expands the phenotypic spectrum of PACS1-RD by reporting median age at independent walking and first spoken words (both 24 months), cross-sectional growth parameters, and previously undescribed clinical features, including congenital kidney malformations (25%) and feeding difficulties (75%). Compared with the literature, our series showed a higher prevalence of cryptorchidism (77.8%), congenital heart defect (45.8%), and hypotonia (75%). Methylation analysis identified a specific episignature for PACS1-RD, consistently observed in individuals carrying either the canonical p.(Arg203Trp) or the non-recurrent p.(Arg203Gln) variant. This episignature further enabled PACS1-RD diagnosis in one unsolved individual initially suspected of Kabuki syndrome. These findings refine the clinical delineation of PACS1-RD and establish an episignature that will support diagnosis in unresolved neurodevelopmental disorders and guide pathogenicity assessment of non-recurrent PACS1 variants.