Comprehensive Clinical Characteristics, Longitudinal Adaptive Functioning, and Electroencephalogram Activity in MAPK8IP3-Related Neurodevelopmental Disorder.

Mitogen-activated protein kinase 8-interacting protein 3-related neurodevelopmental disorder (MAPK8IP3-related NDD) results from heterozygous pathogenic or likely pathogenic variants in MAPK8IP3. We report on 32 individuals (median age 7.5 years, range 1.3-22.0), all of whom had heterozygous pathogenic/likely pathogenic MAPK8IP3 variants, including missense (62.5%) and predicted loss-of-function (LOF) variants (34.4%). Common symptoms included cognitive impairment, hypotonia, motor difficulties, strabismus, microcephaly, and attention deficits. Corpus callosum thinning was reported in 62.1%. Nearly all individuals walked independently but demonstrated slower gait speed and a wider base of support compared to controls. The mean DAS-II General Conceptual Ability score was 62.5 ± 26.5. EEG analysis suggested a trend toward lower power accentuated frequency compared to typically developing individuals. Missense variants were associated with more severe symptoms than LOF variants. This study provides valuable insights into the clinical characteristics, patient management, and preparation for future clinical trials.