The role of pcdh19 during early embryonic development and its implications in pediatric epilepsy

• Applicant: Dr. Barbara Robens
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Developmental Neurobiology
• Term: from 2019 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 424602704

Epilepsy is one of the most common neurological disorders worldwide, affecting almost 1% of the world’s population. As of today, there is no general cure, and a substantial proportion of patients remain refractory to medical or even surgical management. Single gene mutations, or pathogenic variants, are well known causes of epilepsy, with PCDH19 being among the most frequently clinically encountered genes. Pathogenic variants in PCDH19 have been associated with a syndrome called X-linked “PCDH19 girls clustering epilepsy” (PCDH19-GCE), characterized by early onset seizures, intellectual disability, and autism in females. X-linked diseases typically show more severe phenotypes in males than females. Curiously, males with PCDH19 mutations, however, are apparently spared and have no major clinical abnormalities. In females, one of the two X chromosomes is randomly inactivated in each cell, leading to tissue mosaicism. In girls who harbor a variant in one copy of PCDH19, this leaves some cells expressing the wildtype and some expressing the mutant PCDH19 protein. All together, these observations suggest that cellular heterogeneity leads to developmental abnormalities resulting in epileptic seizures. PCDH19 is a protocadherin that is highly expressed during brain development. Unanswered questions include the role of PCDH19 in brain development and how its function is disrupted by mosaic expression but apparently not by the complete absence of the protein, for example, in variant-carrying males. Therefore, treatment of individuals with PCDH19-related epilepsy is still empiric and often unsuccessful, indicating the need for innovative and tailored therapeutic strategies. The failure to provide adequate treatment for these patients is in part due to the relative lack of animal models of PCDH19-GCE to study the underlying molecular mechanisms that lead to the human disease.In this proposal we will address the question of PCDH19 function during brain development by establishing a PCDH19-GCE zebrafish (Danio rerio) model. We will generate transgenic fish by CRISPR/Cas9-mediated genome editing, based on the type and location of PCDH19 variants found in patients and characterize them carefully in regard to the epilepsy and other related phenotypes that arise with different types of mutations. These models will enable us to answer fundamental questions about where and when pcdh19 is expressed in the developing brain, the cell types involved in the pathogenic context, and what key functions it plays during development. There are established phenotyping strategies for evaluating the behavior of zebrafish with respect to seizures and behavioral abnormalities that we will employ in our study. Taken together, this proposal will shed more light into PCDH19 function with the ultimate goal of enabling drug screening in our animal models, as has been achieved for SCN1A, with the intended result of more individualized treatment options for PCDH19-GCE affected children.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professorin Annapurna Poduri, Ph.D.