A CRISPR-Cas9-engineered mouse model for GPI anchor deficiency mirrors human phenotype and shows hippocampal synaptic dysfunctions

Pathogenic germline mutations in lead to glycosylphosphatidylinositol biosynthesis deficiency (GPIBD). Individuals with pathogenic biallelic mutations in genes of the glycosylphosphatidylinositol (GPI) anchor pathway show cognitive impairments, a motor delay and in many cases epilepsy. Thus far, the pathophysiology underlying the disease remains unclear and suitable rodent models that mirror human pathophysiology have not been available. We therefore generated a mouse model using CRISPR-Cas9 to introduce the most prevalent hypomorphic missense mutation in European patients, at a site that is also conserved in mice, :c.1022C>A (p.A341E). Reflecting the human pathology mutant mice showed deficits in motor coordination and cognitive impairment with poorer long-term spatial memory than wild-type mice, as well as alterations in sociability and sleep patterns. Furthermore, immunohistochemistry showed decreased synaptophysin-immunoreactivity and electrophysiology recordings demonstrated reduced hippocampal synaptic transmission in mice that may underlie impaired memory formation. In single-cell RNA sequencing, -hippocampal cells exhibited changes in gene expression, most prominently in a subtype of microglia and subicular neurons. A significant reduction of transcripts in several cell clusters suggests a link to the signaling pathway of GPI-anchored ephrins. We also observed increased levels of that might affect histamine metabolism with consequences in circadian rhythm. This new mouse model will not only open the doors for further investigation into the pathophysiology of GPIBD in future studies, but will also deepen our understanding in the role of GPI anchor related pathways in brain development.