Intellectual development in Noonan syndrome: A longitudinal study

Abstract

Objective: While cognitive impairments in adults with Noonan syndrome (NS) seem to be limited to a low-average intelligence and slower processing speed, studies in children with NS have demonstrated more extensive cognitive problems (e.g. deficits in language, memory, attention, and executive functioning). This longitudinal study is the first to investigate intellectual development in patients with NS. Although childhood IQ is expected to be lower than adult IQ, it is assumed to be a significant predictor of adult intelligence. Participants and Methods: Sixteen patients with NS underwent intelligence assessment in childhood and in adulthood, using Wechsler's intelligence scales. IQ scores and Wechsler standard scores achieved in childhood and adulthood were compared. Childhood verbal and performance IQ (VIQ/PIQ) were included as predictors in multiple regression analyses for adult IQ and index scores. Results: Compared with childhood scores, adult full-scale IQ (FSIQ) and PIQ significantly increased (FSIQ: t(15)= 2.88, p= .01, n2= .36; PIQ: t(15)= 5.49, p< .001, n2= .67). Adult PIQ was higher than VIQ (t(15)= -2.23, p= .04, n2= .25). Childhood PIQ and VIQ together predicted all adult IQ and index scores (adjusted R2> .62, F> 13.32, p<.001), except for processing speed. Conclusions: In accordance with the hypothesis, childhood IQ significantly predicted adult intelligence in patients with NS. PIQ advanced to a normal level in adulthood, while VIQ did not develop proportionately, resulting in a discrepancy between adult PIQ and VIQ. This may suggest a delay in the development of executive functioning in patients with NS, which seems to be outgrown in adulthood.