Observations on intelligence and behavior in 15 patients with Legius syndrome.

Legius syndrome is a RAS-MAPK syndrome characterized by pigmentary findings similar to neurofibromatosis type 1 (NF1), but without tumor complications. Learning difficulties and behavioral problems have been reported to be associated with Legius syndrome, but have not been studied systematically. We investigated intelligence and behavior in 15 patients with Legius syndrome and 7 unaffected family members. We report a mean full-scale IQ of 101.57 in patients with Legius syndrome, which does not differ from the control group. We find a significantly lower Performance IQ in children with Legius syndrome compared to their unaffected family members. Few behavioral problems are present as assessed by the Child Behavior Checklist (CBCL) questionnaire. Our observations suggest that, akin to the milder somatic phenotype, the cognitive phenotype in Legius syndrome is less severe than that of NF1.