Reversibility and developmental neuropathology of linear nevus sebaceous syndrome caused by dysregulation of the RAS pathway.

Linear nevus sebaceous syndrome (LNSS) is a neurocutaneous disorder caused by somatic gain-of-function mutations in KRAS or HRAS. LNSS brains have neurodevelopmental defects, including cerebral defects and epilepsy; however, its pathological mechanism and potentials for treatment are largely unclear. We show that introduction of KRAS in the developing mouse cortex results in subcortical nodular heterotopia and enhanced excitability, recapitulating major pathological manifestations of LNSS. Moreover, we show that decreased firing frequency of inhibitory neurons without KRAS expression leads to disrupted excitation and inhibition balance. Transcriptional profiling after destabilization domain-mediated clearance of KRAS in human neural progenitors and differentiating neurons identifies reversible functional networks underlying LNSS. Neurons expressing KRAS show molecular changes associated with delayed neuronal maturation, most of which are restored by KRAS clearance. These findings provide insights into the molecular networks underlying the reversibility of some of the neuropathologies observed in LNSS caused by dysregulation of the RAS pathway.