FZR1, which encodes the Cdh1 subunit of the Anaphase Promoting Complex, plays an important role in neurodevelopment by regulating the cell cycle and by its multiple post-mitotic functions in neurons. In this study, evaluation of 250 unrelated patients with developmental and epileptic encephalopathies and a connection on GeneMatcher led to the identification of three de novo missense variants in FZR1. Whole-exome sequencing in 39 patient-parent trios and subsequent targeted sequencing in an additional cohort of 211 patients was performed to identify novel genes involved in developmental and epileptic encephalopathy. Functional studies in Drosophila were performed using three different mutant alleles of the Drosophila homolog of FZR1 fzr. All three individuals carrying de novo variants in FZR1 had childhood onset generalized epilepsy, intellectual disability, mild ataxia and normal head circumference. Two individuals were diagnosed with the developmental and epileptic encephalopathy subtype Myoclonic Atonic Epilepsy. We provide genetic-association testing using two independent statistical tests to support FZR1 association with developmental epileptic encephalopathies. Further, we provide functional evidence that the missense variants are loss-of-function alleles using Drosophila neurodevelopment assays. Using three fly mutant alleles of the Drosophila homolog fzr and overexpression studies, we show that patient variants can affect proper neurodevelopment. With the recent report of a patient with neonatal-onset with microcephaly who also carries a de novo FZR1 missense variant, our study consolidates the relationship between FZR1 and developmental epileptic encephalopathy, and expands the associated phenotype. We conclude that heterozygous loss-of-function of FZR1 leads to developmental epileptic encephalopathies associated with a spectrum of neonatal to childhood onset seizure types, developmental delay and mild ataxia. Microcephaly can be present but is not an essential feature of FZR1-encephalopathy. In summary, our approach of targeted sequencing using novel gene candidates and functional testing in Drosophila will help solve undiagnosed myoclonic atonic epilepsy or developmental epileptic encephalopathy cases.
FZR1, which encodes the Cdh1 subunit of the Anaphase Promoting Complex, plays an important role in neurodevelopment, both through the control of the cell cycle and through its multiple functions in post-mitotic neurons. In this study, the evaluation of 250 unrelated patients with developmental epileptic encephalopathies (DEE) and a connection on GeneMatcher led to the identification of three de novo missense variants in FZR1. Two variants led to the same amino acid change. All individuals had a DEE with childhood-onset generalized epilepsy, intellectual disability, mild ataxia, and normal head circumference. Two individuals were diagnosed with the DEE subtype Myoclonic Atonic Epilepsy (MAE). We provide gene burden testing using two independent statistical tests to support FZR1 association with DEE. Further, we provide functional evidence that the missense variants are loss-of-function (LOF) alleles using Drosophila neurodevelopment assays. Using three fly mutant alleles of the Drosophila homolog fzr and overexpression studies, we show that patient variants do not support proper neurodevelopment. Along with a recent report of a patient with neonatal-onset DEE with microcephaly who also carries a de novo FZR1 missense variant, our study consolidates the relationship between FZR1 and DEE, and expands the associated phenotype. We conclude that heterozygous LOF of FZR1 leads to DEE associated with a spectrum of neonatal to childhood-onset seizure types, developmental delay, and mild ataxia. Microcephaly can be present but is not an essential feature of FZR1-encephalopathy. In summary, our approach of targeted sequencing using novel gene candidates and functional testing in Drosophila will help solve undiagnosed MAE/DEE cases.
Prime editing (PE) is currently the most effective and versatile technology to make targeted alterations in the genome. Several improvements to the PE machinery have recently been made, and have been tested in a range of model systems, including immortalized cell lines, stem-cells and animal models. While nick RNA (ncRNA)-dependent PE systems like PE3 and PE5 are currently considered to be the most effective, they come with undesired indels or SNVs at the edit locus. Here, we aimed to improve ncRNA-independent systems PE2 and PE4max by generating novel all-in-one (pAIO) plasmids, driven by a tissue-broad EF-1alpha promoter, that is especially suitable for human iPSC models, and linked to a GFP tag for fluorescent based sorting. These novel pAIO systems effectively corrected mutations observed in patients suffering from epileptic encephalopathy, including a truncating SCN1A R612* variant in HEK293T cells and a gain-of-function KCNQ2 R201C variant in patient-derived hiPSC, with edit efficiency up to 50%. We also show that introducing additional silent PAM-removing mutations can negatively influence edit efficiency. Finally, we observed an absence of genome-wide PE off-target effects at pegRNA homology sites. Taken together, our study shows an improved efficacy and accuracy of EF-1alpha driven ncRNA-independent pAIO PE plasmids in hiPSC.
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