Yale University researchers have identified a molecular mechanism driving the structural abnormalities leading to lissencephaly that have, until recently, been elusive. Further, this research, published in Nature, offers a path for potential treatments.
“Lissencephaly belongs to a group of disorders we call malformations of cortical development,” said Angeliki Louvi, MD, professor of neurosurgery and neuroscience, Yale School of Medicine (YSM) and co-senior author of the study. They are caused by rare mutations in select genes that are important for brain development.
Lissencephaly spectrum disorders are a rare group of genetic disorders characterized by a lack of cortical folding, resulting in seizures and intellectual disabilities in affected individuals. In the new study, the Yale team built upon the research of co-senior author, Murat Gunel, MD, the Sterling Professor of Neurosurgery and professor of genetics and neuroscience, YSM. Using whole genome sequencing (WGS) to identify common mutations within lissencephaly patients and create cerebral organoids from patient cells, the team identified a CRISPR-Cas9 treatment that may prevent and reverse the effects of lissencephaly-causing mutations.
The study was published in an article titled, “Dysregulation of mTOR signaling is a converging mechanism in lissencephaly.”
The authors used WGS to identify recessive mutations in the p53-induced death domain protein 1 gene (PIDD1) in individuals within the Yale Neurogenetics cohort. Using hair follicle-derived cells from lissencephaly patients within the cohort and non-affected family members as controls, the team created induced pluripotent stem (iPS) cells, which they then grew into organoids. The organoid models exhibited thickened cortex-like structures, a hallmark seen in lissencephaly along with the lack of folding.
Gene and protein expression analysis of the organoids revealed dysregulation in the mTOR (mammalian target of rapamycin) pathway, which is critical for human cortical development.
“This is a fundamental pathway that governs many different aspects of cellular metabolism to maintain cellular homeostasis,” said Louvi. In lissencephaly, mTOR has reduced function, so the researchers aimed to increase activity in the organoids.
Next, CRISPR-Cas9 gene editing was used to effect functional changes in the organoids by introducing the wild-type allele of PIDD1. The resulting organoids showed a reversal of the thickening in cortical plate-like areas seen in the untreated organoids.
“Right now, in medicine, we have no way to slow or reverse these structural brain malformations in lissencephaly either during pregnancy or after,” said lead author Ce Zhang, MD, PhD, a resident at Cedars-Sinai Medical Center. “That limits us to treating the symptoms, but even that can be difficult, as lissencephaly seizures may not be well-controlled using typical anti-epileptic drugs.”
The Yale study highlights the possibility that a single treatment targeting the mTOR pathway, such as CRISPR-Cas9 treatment, could be effective across the lissencephaly spectrum. “If there’s a converging pathway shared between these disorders, regardless of the genetic cause, it could mean one treatment might be beneficial to patients across the lissencephaly spectrum,” Zhang said.
The team plans to continue unfolding the intricacies of the mTOR pathway’s function in other genetic types of lissencephaly and delve deeper into the molecular consequences of an underactive mTOR pathway.
“These findings extend our knowledge of this pathway, highlighting the fine balance that has to be met for healthy brain development,” said Louvi. “Now we want to understand what exactly happens molecularly when mTOR is underactivated.”
