Intelligence quotient in adults with idiopathic hypersomnia and narcolepsy type 1

Given that intelligence quotient (IQ) has not previously been assessed in idiopathic hypersomnia (IH) and only rarely in adults with narcolepsy type 1 (NT1), this study examined IQ in adults with IH and NT1.

The Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV), comprising the Full Scale IQ, four indices and 10 subtests, was administered to 29 participants with IH (22 women; age: 34.1 ± 11.3 y [mean ± SD]; Epworth Sleepiness Scale [ESS] score: 12.4 ± 4.7), 30 with NT1 (19 women; age: 30.1 ± 10.6 y; ESS: 15.5 ± 5), and 30 healthy controls (21 women, age: 30.7 ± 8.7 y; ESS: 5.0 ± 3.6).

Full-Scale IQ scores differed across groups (IH: 114.6 ± 13.4; NT1: 104.1 ± 14.3; and controls: 108.4 ± 17.0; p = 0.03, medium effect size). Both IH and NT1 groups showed IQ comparable to controls, although IH participants tended to outperform those with NT1. Group differences emerged in the perceptual reasoning and working memory domains, although none of pairwise comparisons reached significance. The only cognitive area showing group differences was visuospatial reasoning. Global cognitive abilities, including Full-scale IQ, General Ability Index, Verbal Comprehension Index and Working Memory Index showed moderate correlation with years of education, though not with disease duration, daytime sleepiness or treatment status. Pre-test fatigue, though not daytime sleepiness, was associated with poorer working memory performances.

Adults with IH and NT1 exhibit normal-range IQs despite chronic hypersomnolence and cognitive complaints. Emphasizing preserved intellectual functioning may contribute to enhanced self-esteem and support professional development in these populations.