Pcdh19, encoding protocadherin 19, is a gene located in Xq22 and produces nonclustered delta protocadherin. The protein it encodes is highly expressed during brain development and may play roles in neuronal migration or establishing synaptic connections, potentially regulating gamma-aminobutyric acid type A receptors (GABA(A)(R)) [3,4].

PCDH19-related epilepsy is a distinct childhood-onset epilepsy syndrome. Heterozygous PCDH19 mutations cause this disorder mainly in females due to random X-chromosome inactivation leading to somatic mosaicism and abnormal cellular interference. Studies with zebrafish and murine models have provided insights into the function of PCDH19 during brain development and how its altered function causes the disease, though they fail to fully reproduce the human phenotype. Induced pluripotent stem cell (iPSC) technology, including the development of 3D brain organoids, may help further investigate the pathomechanisms [1,2,5].

In conclusion, Pcdh19 is crucial for brain development, especially in processes related to neuronal migration and synaptic connection establishment. Mouse models and other genetic models have been valuable in understanding its role in the context of PCDH19-related epilepsy, a disorder with unique inheritance patterns. However, more research, including the use of iPSC-based models, is needed to fully understand its function and the disease mechanisms [1,2,3,5].