Wide Ranging Neurobehavioral Phenotype in Individuals With Costello Syndrome

Costello syndrome (CS) is a rare RASopathy that is typically associated with mild to moderate cognitive impairment. Based on detailed neuropsychological testing, this case series describes variability in the neurobehavioral presentations of three unrelated individuals with different pathogenic HRAS variants that cause CS. Results demonstrate a wide range of functioning among people with CS (extremely low to superior ranges) and describe the first cognitive testing results for an individual with HRAS c.179G>A, p.Gly60Asp. Patient‐reported social, emotional, and quality of life outcomes also are discussed. These cases highlight the potential for above average cognitive functioning, the importance of flexible neurobehavioral assessment methods, and key quality of life and mental health domains to evaluate in individuals with CS.