Heterogeneity of comprehensive clinical phenotype and longitudinal adaptive function and correlation with computational predictions of severity of missense genotypes in KIF1A-associated neurological disorder

Purpose Pathogenic variants in Kinesin Family Member 1A ( KIF1A ) are associated with KIF1A -associated neurological disorder (KAND). We report the clinical phenotypes and correlate genotypes of individuals with KAND. Methods Medical history and adaptive function were assessed longitudinally. In-person evaluations included neurological, motor, ophthalmologic and cognitive assessments. Results We collected online data on 177 individuals. Fifty-seven individuals were also assessed in-person. Most individuals had de novo heterozygous missense likely pathogenic/pathogenic KIF1A variants. The most common characteristics were hypotonia, spasticity, ataxia, seizures, optic nerve atrophy, cerebellar atrophy, and cognitive impairment. Mean Vineland Adaptive Behavior Composite score (VABS-ABC) was low ( M =62.9, SD =19.1). The mean change in VABS-ABC over time was -3.1 ( SD =7.3). The decline in VABS-ABC was associated with the age at first assessment and abnormal electroencephalogram/seizure. There was a positive correlation between Evolutionary Scale Model (ESM) score for the variants and final VABS-ABC ( p =0.003). Abnormal electroencephalogram/seizure, neuroimaging result, and ESM explain 34% of the variance in final VABS-ABC ( p <0.001). Conclusion In-person assessment confirmed caregiver report and identified additional visual deficits. Adaptive function declined over time consistent with both the neurodevelopmental and neurodegenerative nature of the condition. Using ESM score assists in predicting phenotype across a wide range of unique variants.