P387: Comprehensive genetic evaluation in a male with congenital thrombocytopenia, hearing loss, and developmental delay: Expanding the RAP1B phenotype

were noted.Clinical trio short-read genome sequencing (GS) including both unaffected parents was performed, revealing two de novo pathogenic variants in PTPN11.One variant [c.1403C>T, p.(T468M)] is well-established for NSML, whereas the second variant [c.1374C>G, p.(H458Q)] is less understood in mechanism, pathogenicity, and phenotype.Phasing of these variants could not be determined by available short-read sequencing as they were on different exons ~1,800 nucleotides apart.Diagnostic Workup: Oxford Nanopore Technologies (ONT) long-read GS, including variant calling and methylation analysis, was conducted from the proband's peripheral blood.Sequence reads were analyzed using Integrative Genomics Viewer (IGV) to determine PTPN11 variant phasing and methylation status.Manual analysis of reads demonstrated that both PTPN11 variants were in cis configuration.Methylation analysis confirmed loss of methylation at the [c.1403C>T, p.(T468M)] variant, while the [c.1374C>G, p.(H458Q)] variant remained unmethylated.