P658: Prognostic factors for pediatric osteosarcoma

the ATXN2 expansion later confirmed by PCR.One case (GLS) also exhibited strong correlation, although the expansion was in a heterozygous state with no second variant identified.In the remaining 5 cases, limited or absent clinical data prevented adequate assessment of genotype-phenotype correlation.Conclusion: This study highlights the utility of ExpansionHunter for detecting STR expansions in ES data, emphasizing its potential in clinical diagnostic workflows.Of the 19 identified cases, 14 were supported after visual inspection, with 9 showing strong genotype-phenotype correlation, including cases linked to ATXN2, ATXN7, DMPK, and GLS.This represents an improved accuracy of approximately 0,2% in an unselected pool of ES samples.The exclusion of five likely false-positive results underscores the importance of integrating visual validation tools such as REViewer to ensure diagnostic accuracy.While ExpansionHunter proves to be a valuable tool for analyzing STR expansions, its application would benefit from further optimization to reduce false-positive rates in ES.This real-world evaluation supports the integration of STR expansion analysis into routine diagnostic pipelines for inherited disorders.