Novel Approach to Improve the Identification of the Bleeding Phenotype in Noonan Syndrome and Related RASopathies

Objectives To characterize the bleeding phenotype in Noonan syndrome (NS), to test the utility of following national guidelines in detecting this phenotype, to evaluate thromboelastography (TEG) as a diagnostic tool, and to evaluate the cohort for genotype-phenotype correlations. Study design Participants with a clinical diagnosis of NS or related RASopathies were enrolled in a cohort study. Study procedures included clinical bleeding assessment, coagulation testing per guidelines, and hematology consultation. TEG was completed in a subset, and genetic testing was conducted for those without a molecular diagnosis. International Society of Haemostasis and Thrombosis Bleeding Assessment Tool scores were calculated with hematology consultation. Bleeding phenotype was defined as abnormal bleeding score. Results Twenty participants were enrolled; 12 completed clinical and laboratory evaluation, and five of whom met the definition for bleeding phenotype. Four of the five participants with a bleeding phenotype had platelet aggrega-tion defects and at least one additional coagulation defect. TEG was performed in nine participants, four with bleeding phenotype and five without, and results were normal in all cases. No genotype-phenotype correlation was found. Conclusion Five of the 20 participants had a bleeding phenotype identified. Based on available data, we do not recommend incorporating TEG into clinical practice for patients with NS. Platelet aggregation defects were the most common abnormalities, which would not be detected on tier 1 testing of current guidelines; therefore, we propose a new algorithm.