RESUMO
Valid clinical outcome assessments with the ability to capture meaningful aspects of neurodevelopment for individuals with neurogenetic conditions associated with profound functional impairments are lacking, yet critical for clinical care and clinical trial readiness. The purpose of this pilot study was to examine and compare the initial psychometric properties of a series of commonly used standardized and norm-referenced measures of cognition and adaptive functioning as well as alternative measures of neurobehavioral functioning designed to capture responsivity (i.e., alertness, awareness, responsivity to the environment) in those with acquired brain injuries in a sample of individuals with severe to profound functional impairment associated with a neurogenetic etiology. Ten individuals (median age = 7.5 years, IQR = 4.8-11.5, range 4-21; n = 8 male) with severe to profound functional impairment associated with SCN2A-Related Disorder and their parents were included in this study. Parents completed the Vineland Adaptive Behavior Scales, Third Edition Comprehensive Interview (Vineland-3) and the Developmental Profile, Fourth Edition Cognitive Scale (DP-4) and their children completed the Bayley Scales of Infant and Toddler Development Cognitive Scale (Bayley-4; given out of the standardized age-range) and two measures of responsivity, the Coma Recovery Scale, Pediatric and the Rappaport Coma/Near Coma Scale. Results demonstrated exceptionally low skills (median Vineland-3 Adaptive Behavior Composite = 35.5) and frequent floor effects across norm-referenced measures (i.e., Vineland-3, DP-4, Bayley-4); however, raw scores yielded more range and variability and no absolute floor effects. There were also no floor effects on measures of responsivity and findings suggest that these alternative tools may capture more variability in some aspects of neurobehavioral functioning that are critical to higher order cognitive functions, particularly for those with mental-ages below a 12 month-level. Initial evidence of construct validity of all measures in this population was shown. Findings support ongoing investigation of measures of responsivity and identified areas of potential measure modification that may improve applicability for individuals with severe to profound functional impairment associated with neurogenetic as opposed to acquired etiologies.
RESUMO
SCN2A-related disorders secondary to altered function in the voltage-gated sodium channel Nav1.2 are rare, with clinically heterogeneous expressions that include epilepsy, autism and multiple severe to profound impairments and other conditions. To advance understanding of the clinical phenotypes and their relationship to channel function, 81 patients (36 female, 44%, median age 5.4 years) with 69 unique SCN2A variants were systematically phenotyped and their Nav1.2 channel function systematically assessed. Participants were recruited through the FamileSCN2A Foundation. Primary phenotype (epilepsy of neonatal onset, n = 27; infant onset, n = 18; and later onset n = 24; and autism without seizures, n = 12) was strongly correlated with a non-seizure severity index (P = 0.002), which was based on presence of severe impairments in gross motor, fine motor, communication abilities, gastrostomy tube dependence and diagnosis of cortical visual impairment and scoliosis. Non-seizure severity was greatest in the neonatal-onset group and least in the autism group (P = 0.002). Children with the lowest severity indices were still severely impaired, as reflected by an average Vineland Adaptive Behavior composite score of 49.5 (>3 standard deviations below the norm-referenced mean of the test). Epileptic spasms were significantly more common in infant-onset (67%) than in neonatal (22%) or later-onset (29%) epilepsy (P = 0.007). Primary phenotype was also strongly correlated with variant function (P < 0.0001); gain-of-function and mixed function variants predominated in neonatal-onset epilepsy, shifting to moderate loss of function in infant-onset epilepsy and to severe and complete loss of function in later-onset epilepsy and autism groups. Exploratory cluster analysis identified five groups, representing: (i) primarily later-onset epilepsy with moderate loss-of-function variants and low severity indices; (ii) mostly infant-onset epilepsy with moderate loss-of-function variants but higher severity indices; and (iii) late-onset and autism only, with the lowest severity indices (mostly zero) and severe/complete loss-of-function variants. Two exclusively neonatal clusters were distinguished from each other largely on non-seizure severity scores and secondarily on variant function. The relationship between primary phenotype and variant function emphasizes the role of developmental factors in the differential clinical expression of SCN2A variants based on their effects on Nav1.2 channel function. The non-seizure severity of SCN2A disorders depends on a combination of the age at seizure onset (primary phenotype) and variant function. As precision therapies for SCN2A-related disorders advance towards clinical trials, knowledge of the relationship between variant function and clinical disease expression will be valuable for identifying appropriate patients for these trials and in selecting efficient clinical outcomes.