General mental ability (Spearman's g) in Juvenile Myoclonic Epilepsy

Objective: To: (a) interrogate the concept of general mental ability reflected by “Spearman's g” factor in participants with Juvenile Myoclonic Epilepsy (JME) and control participants; (b) understand g's clinical, familial, socioeconomic, and brain structural correlates; and (c) determine g's relationship with variable cognitive pathology in JME and the neuroanatomical correlates of association. Methods: Seventy-seven JME and 43 typically developing unrelated control participants (mean ages 19.7 and 20.3 years, respectively) were administered a comprehensive neuropsychological battery with characterization of clinical epilepsy and familial features, determination of socioeconomic status, and structural neuroimaging. g was estimated through factor analysis and compared between participant groups, related to familial social factors (marital status, level of education, work status), socioeconomic environment (Area Deprivation Index), and brain morphological features (total intracranial volume [TIV], cortical and subcortical volumes, and cortical thickness). High and low cognitive reserve groups were defined by g and interrogated in a similar fashion. Results: General mental ability (g) was significantly lower in JME than in controls and associated with a lower level of paternal education, greater disadvantage, smaller TIV and cortical and subcortical volumes, as well as with disruption of age-appropriate cortical thinning in bifrontal lateral and medial regions. JME high and low g groups exhibited significantly different cognitive and academic profiles compared to controls, as well as to each other, with differences in familial and socioeconomic factors, as well as in brain morphological characteristics, all less favorable in the low compared to high g JME group. High g JME participants showed few differences compared to controls. Significance: g is lower in JME than control participants and linked with definable features of familial and sociodemographic environment, as well as brain morphological patterns. g appears to provide an effective metric to characterize so-called reserve for overall cognitive and academic function with associated brain structural features, notably the presence/absence of age-appropriate cortical thinning in bifrontal regions. Plain language summary: General mental ability, or g, is an important aspect of a person's cognitive ability. We found g to be lower in JME patients compared to controls and to be linked to features of their family, neighborhood, and brain. The protective effects of g could be shown by dividing participants into high and low g groups. High g participants exhibited few differences compared to controls, while, in contrast, low g participants showed poorer cognition, school performance, came from deprived neighborhoods, and had more problematic family features. Importantly, lower g was linked to measures of the brain, suggesting slowed neurodevelopment.