Clinical and Molecular Spectrum of PIK3CA-Related Overgrowth Syndrome: A Turkish Cohort

Background: PIK3CA-related overgrowth spectrum (PROS) includes a group of mosaic overgrowth disorders caused by postzygotic gain-of-function variants in the PIK3CA gene. These variants lead to upregulation of the PI3K/AKT/mTOR signaling pathway, resulting in dysregulated cell growth, proliferation, and vasculogenesis. Disorders such as KTWS and CLOVES syndrome share overlapping clinical features such as segmental overgrowth, vascular and lymphatic malformations, and cutaneous involvement.Methods: A cohort of five Turkish patients with clinical findings consistent with PROS was evaluated. High-depth next-generation sequencing (NGS) was performed on affected tissue samples, and the identified variants on PIK3CA gene were interpreted according to ACMG/AMP criteria. Clinical, radiological, and molecular data were integrated to assess genotype–phenotype correlations.Results: Five distinct somatic PIK3CA variants were identified. Four were in the C-terminal helical and kinase domains—known mutational hotspots—while one variant was found in the N-terminal adaptor-binding (PI3K-ABD) domain. Four variants were missense substitutions, and one was an in-frame deletion. The mean sequencing depth was approximately 1100×, and the lowest variant allele frequency (VAF) detected was 2%. No correlation was observed between VAF and disease severity.Conclusion: This Turkish cohort highlights the clinical and molecular heterogeneity of PROS and emphasizes the importance of tissue-targeted, high-depth sequencing in detecting low-level mosaic variants. Molecular confirmation of PIK3CA mosaicism is essential for accurate diagnosis and therapeutic decision-making. Considering the recent evidence supporting the efficacy of Alpelisib in both pediatric and adult PROS patients, early recognition and molecular characterization of these cases are critical for guiding precision therapy and improving clinical outcomes.