Developmental epileptic encephalopathies (DEEs) are a group of severe neurological disorders that present with seizures in early infancy and developmental delays. A genetic cause can be identified in up to 50% of affected individuals and is most commonly a de novo genetic change. However, for some patients a genetic change is not evident through DNA sequencing. In this research project, we are using RNA sequencing to search for and identify abnormal splicing events that may be due to splice-altering variants in the genome of previously undiagnosed patients. Splicing occurs naturally in unaffected and affected individuals; it is the process of introns being removed from mRNA transcripts and exons being joined. The process of RNA sequencing allows us to discover abnormal splicing errors by looking at splice junctions, which are sites on the intron and exon border where splicing normally occurs. We search for abnormal splicing defects using RNA sequencing by comparing the splice-junctions from our patients to a reference database of healthy controls (Genotype-Tissue Expression Project), filtering out common splice junctions, allowing us to identify unique and abnormal splice junctions. If we identify abnormal splicing, we will also investigate the genome of the patient to determine whether there is an underlying DNA change. Using RNA sequencing, we hope to provide a genetic diagnosis for a subset of our undiagnosed patients and for more individuals affected by DEE in the future.

Many genes are associated with microcephaly, a condition characterized by a small head size. Through exome-sequencing, we identified de novo missense mutations in an actin polymerization gene, ARPC4, in four individuals with microcephaly, mild developmental delay, and mild intellectual disability. ARPC4 is involved in actin filament formation. Actin is an essential component of the cell’s cytoskeleton that gives the cell its structure and aids in cell movement and division. The goal of this research project is to understand the molecular mechanisms that lead to the disease phenotype observed in these patients. I began by using CADD, a measurement used to predict the deleteriousness of single nucleotide variants. The mutations identified in the patients were located in highly conserved loci, indicating they might be pathogenic. To provide further evidence of the pathogenicity of the ARPC4 variants, we were interested in determining the functional effect these variants have on actin polymerization – specifically, the role of ARPC4 in this mechanism. I established fibroblast cell lines from two patients with the same ARPC4 mutation. I performed immunofluorescence staining for actin to quantify the amount of actin present in the patients and control cell lines. Preliminary data from this experiment suggests that there is greater abundance of actin filaments in the control sample compared to the patients’ cells. To observe the effect of decreased actin abundance on cell migration, I executed a scratch migration assay. The results from this study elucidate the impact of ARPC4 in actin polymerization, and establish actin deficiency as a clinically recognizable cause of microcephaly.

The nucleus is the information center of the cell, acting as a hub for DNA storage, regulation, and replication. Therefore, transport of molecules into and out of the nucleus is vital for proper biological functioning. This transport is tightly regulated via the nuclear membrane, and a collection of proteins called nuclear pore proteins that interact with molecular signals. These signals allow molecules that cannot passively diffuse through the nuclear membrane (typically greater than 60 kD) to be shuttled into or out of the nucleus via a variety of pathways. Like all biological pathways, this process can be disrupted and lead to phenotypic abnormalities. Our lab identified two siblings with biallelic variants in NUP188, a known nuclear pore protein; we identified four additional cases in three families through collaborators. Clinical features include brain abnormalities with thin corpus callosum, progressive microcephaly, severely delayed myelination; congenital cataracts; mild dysmorphic features; and hypoventilation leading to death in infancy. In order to better understand our patients’ phenotype, we are investigating nuclear import pathways as a potential mechanism of disease. Using green fluorescent protein (GFP), we can directly visualize protein localization in living cells, without the use of additional stains such as immunohistochemistry. Based on size restriction of the nuclear pore, we used a vector construct with three repeats of GFP and our nuclear localization signal (NLS). Specifically, we are investigating four main NLS pathways: Importin α+β (SV40 NLS), Kap β2 (hnRNP NLS), Importin β (CREB NLS), and no NLS. We have been able to successfully create a viral vector for each NLS. Next steps include optimizing expression in patient cell lines. This approach will allow us to quantify and visualize discrepancies between patient and control localization patterns, leading to better understanding of causes of patient phenotype and potential novel therapies.

 Developmental and epileptic encephalopathies (DEEs) are an early-onset form of epilepsy characterized by intractable seizures and severe cognitive and developmental impairment. While most genetic variants that cause DEE reside in the coding regions of genes, splice-site variants can also be pathogenic. Splice-site variants are changes in the DNA close to, or on, the exon-intron boundary, which can cause aberrant splicing, resulting in exon exclusion or intron inclusion within spliced mRNA, generating a protein that is non-functional, partially functional, or aberrantly expressed. Aberrant splicing can have pathogenic consequences, but predicting which variants near splice-sites will have an effect on splicing is difficult. I am studying three potential splice-site variants in three genes associated with DEE: SYNGAP1, SCN1B, and WWOX. I used RNA extracted from fibroblasts from three DEE patients, each with one of these variants, to confirm whether the splice-site variants cause aberrant splicing and what the predicted consequences of this aberrant splicing is on the protein. I have been able to discover the effects of the variants on splicing in WWOX and SYNGAP1. In SYNGAP1, a synonymous variant at the exon-intron junction caused an exon 4 deletion, resulting in a severely truncated protein (SYNGAP1:p.Glu120Alafs*20). In WWOX, a duplication which included exon 5 resulted in a transcript with the inclusion of two copies of exon 5, leading to a frameshift mutation and predicted truncated protein (WWOX:p.His173Glyfs*13). We are still investigating the effects of the intronic variant in SCN1B, which appears to decrease expression of the gene. We are using nonsense-mediated decay inhibitors in order to better understand the mechanism through which this decreased expression occurs. This research could potentially improve the care of these patients by providing genetic evidence of the causes of DEE, which can be the basis for advancing better treatments.