Rapamycin Prevents Seizures After Depletion of STRADA in a Rare Neurodevelopmental Disorder

Blocking mTORC1 rescues the neural progenitor cell migratory defect caused by depletion of the STRADA pseudokinase and reduces seizures in patients with a rare neurodevelopmental disorder. Preventing Seizures with Rapamycin The discovery of new treatments for rare neurodevelopmental disorders associated with epilepsy and intellectual disability is often limited by small patient sample sizes that delay initiation of clinical trials. Mutations in the gene STRADA cause brain malformations, seizures, and failure to develop social language in children, with no known successful treatment. In a new study, Parker and colleagues now show that the protein STRADA modulates the mammalian target of rapamycin (mTOR) signaling pathway and that loss of STRADA results in unchecked mTOR activity. Depletion of STRADA in mouse neural progenitor cells resulted in loss of polarity, impaired migration, and inability to form layers in the cerebral cortex. Impaired migration was also identified in fibroblasts from patients lacking STRADA, and all of these effects were prevented with the mTOR inhibitor rapamycin, an immunosuppressant drug in clinical use. The authors then treated five children with rapamycin (sirolimus) beginning at 3 to 8 months of age, and abatement of seizures was observed in all of the children. Early treatment with mTOR pathway inhibitors may be beneficial for children with this neurodevelopmental disorder or with other conditions associated with enhanced mTOR signaling such as tuberous sclerosis complex and fragile X syndrome. A rare neurodevelopmental disorder in the Old Order Mennonite population called PMSE (polyhydramnios, megalencephaly, and symptomatic epilepsy syndrome; also called Pretzel syndrome) is characterized by infantile-onset epilepsy, neurocognitive delay, craniofacial dysmorphism, and histopathological evidence of heterotopic neurons in subcortical white matter and subependymal regions. PMSE is caused by a homozygous deletion of exons 9 to 13 of the LYK5/STRADA gene, which encodes the pseudokinase STRADA, an upstream inhibitor of mammalian target of rapamycin complex 1 (mTORC1). We show that disrupted pathfinding in migrating mouse neural progenitor cells in vitro caused by STRADA depletion is prevented by mTORC1 inhibition with rapamycin or inhibition of its downstream effector p70 S6 kinase (p70S6K) with the drug PF-4708671 (p70S6Ki). We demonstrate that rapamycin can rescue aberrant cortical lamination and heterotopia associated with STRADA depletion in the mouse cerebral cortex. Constitutive mTORC1 signaling and a migration defect observed in fibroblasts from patients with PMSE were also prevented by mTORC1 inhibition. On the basis of these preclinical findings, we treated five PMSE patients with sirolimus (rapamycin) without complication and observed a reduction in seizure frequency and an improvement in receptive language. Our findings demonstrate a mechanistic link between STRADA loss and mTORC1 hyperactivity in PMSE, and suggest that mTORC1 inhibition may be a potential treatment for PMSE as well as other mTOR-associated neurodevelopmental disorders.