Cognitive impairments are a major clinical feature of the common neurogenetic disease neurofibromatosis type 1 (NF1). Previous studies have demonstrated that increased neuronal inhibition underlies the learning deficits in NF1, however, the molecular mechanism underlying this cell-type specificity has remained unknown. Here, we identify an interneuron-specific attenuation of hyperpolarization-activated cyclic nucleotide-gated (HCN) current as the cause for increased inhibition in Nf1 mutants. Mechanistically, we demonstrate that HCN1 is a novel NF1-interacting protein for which loss of NF1 results in a concomitant increase of interneuron excitability. Furthermore, the HCN channel agonist lamotrigine rescued the electrophysiological and cognitive deficits in two independent Nf1 mouse models, thereby establishing the importance of HCN channel dysfunction in NF1. Together, our results provide detailed mechanistic insights into the pathophysiology of NF1-associated cognitive defects, and identify a novel target for clinical drug development.

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ObjectiveTo investigate whether mammalian target of rapamycin inhibitor everolimus can improve intellectual disability, autism, and other neuropsychological deficits in children with tuberous sclerosis complex (TSC).MethodsIn this 12-month, randomized, double-blind, placebo-controlled trial, we attempted to enroll 60 children with TSC and IQ <80, learning disability, special schooling, or autism, aged 4–17 years, without intractable seizures to be assigned to receive everolimus or placebo. Everolimus was titrated to blood trough levels of 5–10 ng/mL. Primary outcome was full-scale IQ; secondary outcomes included autism, neuropsychological functioning, and behavioral problems.ResultsThirty-two children with TSC were randomized. Intention-to-treat analysis showed no benefit of everolimus on full-scale IQ (treatment effect −5.6 IQ points, 95% confidence interval −12.3 to 1.0). No effect was found on secondary outcomes, including autism and neuropsychological functioning, and questionnaires examining behavioral problems, social functioning, communication skills, executive functioning, sleep, quality of life, and sensory processing. All patients had adverse events. Two patients on everolimus and 2 patients on placebo discontinued treatment due to adverse events.ConclusionsEverolimus did not improve cognitive functioning, autism, or neuropsychological deficits in children with TSC. The use of everolimus in children with TSC with the aim of improving cognitive function and behavior should not be encouraged in this age group.Clinicaltrials.gov identifierNCT01730209.Classification of evidenceThis study provides Class I evidence that for children with TSC, everolimus does not improve intellectual disability, autism, behavioral problems, or other neuropsychological deficits.