Phenotypic and Genotypic Characterization of NPRL2-Related Epilepsy: Two Case Reports and Literature Review

Clinical phenotype and genotype of NPRL2-related epilepsy: Four cases reports and literature review

BACKGROUND

NPRL2-related epilepsy, caused by pathogenic germline variants of the NPRL2 gene, is a newly discovered childhood epilepsy linked to enhanced mTORC1 signalling. However, the phenotype and genotype of NPRL2 variants are still poorly understood. Here, we summarize the association between the phenotype and genotype of NPRL2-related epilepsy.

METHODS

A retrospective analysis was conducted for four Chinese children with epilepsy due to likely pathogenic NPRL2 variants identified through whole-exome sequencing (WES). Previous reports of patients with NPRL2-related epilepsy were reviewed systematically.

RESULTS

One of our patients presented focal epilepsy involving the central region, which should be distinguished from self-limited epilepsy with centrotemporal spikes (SeLECTS). The four novel likely pathogenic NPRL2 variants consisted of two nonsense variants, one frameshift variant, and one copy number variant (CNV). Bioinformatics analysis revealed the two nonsense variants to be highly conserved and cause alterations in protein structure. Including our four cases, a total of 33 patients with NPRL2-related epilepsy have been identified to date. The most common presentation is focal epilepsy (70%), including sleep-related hypermotor epilepsy (SHE), temporal lobe epilepsy (TLE), and frontal lobe epilepsy (FLE). Infantile epileptic spasms syndrome (IESS) is also a notable feature of NPRL2-related epilepsy. Malformations of cortical development (MCD, 8/20), especially focal cortical dysplasia (FCD, 6/20), are common neuroimaging abnormalities. Two-thirds of the NPRL2 variants reported are loss of function (LoF) (14/21). Among these mutations, c.100C>T (p.Arg34*) and c.314T>C (p.Leu105Pro) have been detected in two families (likely due to a founder effect).

CONCLUSION

NPRL2-related epilepsy shows high phenotypic and genotypic heterogeneity. Our study expands the genotype spectrum of NPRL2-related epilepsy, and the phenotype of focal epilepsy involving the central region should be clearly distinguished with SeLECTS, with reference value for clinical diagnosis.

GATOR1 Mutations Impair PI3 Kinase-Dependent Growth Factor Signaling Regulation of mTORC1

GATOR1 (GAP Activity TOward Rag 1) is an evolutionarily conserved GTPase-activating protein complex that controls the activity of mTORC1 (mammalian Target Of Rapamycin Complex 1) in response to amino acid availability in cells. Genetic mutations in the GATOR1 subunits, NPRL2 (nitrogen permease regulator-like 2), NPRL3 (nitrogen permease regulator-like 3), and DEPDC5 (DEP domain containing 5), have been associated with epilepsy in humans; however, the specific effects of these mutations on GATOR1 function and mTORC1 regulation are not well understood. Herein, we report that epilepsy-linked mutations in the NPRL2 subunit of GATOR1, NPRL2-L105P, -T110S, and -D214H, increase basal mTORC1 signal transduction in cells. Notably, we show that NPRL2-L105P is a loss-of-function mutation that disrupts protein interactions with NPRL3 and DEPDC5, impairing GATOR1 complex assembly and resulting in high mTORC1 activity even under conditions of amino acid deprivation. Furthermore, our studies reveal that the GATOR1 complex is necessary for the rapid and robust inhibition of mTORC1 in response to growth factor withdrawal or pharmacological inhibition of phosphatidylinositol-3 kinase (PI3K). In the absence of the GATOR1 complex, cells are refractory to PI3K-dependent inhibition of mTORC1, permitting sustained translation and restricting the nuclear localization of TFEB, a transcription factor regulated by mTORC1. Collectively, our results show that epilepsy-linked mutations in NPRL2 can block GATOR1 complex assembly and restrict the appropriate regulation of mTORC1 by canonical PI3K-dependent growth factor signaling in the presence or absence of amino acids.

Precision Medicine in Epilepsy Management; GET Application (Gene, Epilepsy, Treatment)

OBJECTIVES

The aim was to develop a prototype of an application (app) that identifies the significance of discovered genes for further consideration in the treatment plan of patients with epilepsy (precision medicine).

METHODS

MEDLINE was systematically searched for related publications from inception to April 1, 2022. The following search strategy was implemented (title/abstract): "epilepsy" AND "precision" AND "medicine." The following data were extracted: genes, phenotypes associated with those genes, and the recommended treatments. Two other databases were searched to cross-check the retrieved data and add to the data: https://www.genecards.org and https://medlineplus.gov/genetics. Also, the original articles of the identified genes were retrieved. Genes with specific treatment strategies (ie, any specific drug to be selected or to be avoided and also any other specific therapies [eg, diets, supplements, etc]) were selected.

RESULTS

A database of 93 genes, which are associated with various epilepsy syndromes and for which specific treatment strategies have been suggested, was developed.

CONCLUSIONS

A Web-based app (a search engine) was developed accordingly that is freely available at http://get.yektaparnian.ir/, GET (Gene, Epilepsy, Treatment). When a patient comes to the clinic with a genetic diagnosis and a specific gene is identified, the physician enters the gene name into the search box, and the app shows whether this genetic epilepsy needs a specific treatment. This endeavor would benefit from input by experts in the field, and the Web site should be developed more comprehensively.

Clinical phenotypic and genotypic characterization of NPRL3-related epilepsy

Background

As one of the assembly factors of the GATOR1 protein complex in the mechanism of rapamycin pathway, NPRL3 plays an important role in the pathogenesis of epilepsy. However, the correlation between genotype and clinical phenotype in patients with NPRL3-related epilepsy has not been clarified.

Methods

A total of 11 Chinese children with NPRL3-related epilepsy were identified through whole-exome sequencing (WES). The data from the clinical presentation, laboratory data, brain imaging findings, genetic results, and treatment methods were collected. All previously reported cases with NPRL3-related epilepsy were collected and reviewed through PubMed search.

Results

Among the 11 children, eight have not been reported, and two of them presented infantile spasms (ISs) as a new phenotype of NPRL3-related epilepsy. In addition, WES identified five frameshift mutations, three nonsense mutations, two missense mutations, and one exon deletion. Based on bioinformatics analysis, it was found that two missense mutation sites were highly conserved, and the c.400G>A mutation site of the NPRL3 gene caused the alteration of the protein structure. To date, 88 patients have been reported with NPRL3-related defects, including our 11 cases. The most common presentations were sleep-related hypermotor epilepsy (SHE), frontal lobe epilepsy (FLE), and temporal lobe epilepsy. A majority of patients (70%) presented normal neuroimaging results, and focal cortical dysplasia was the most common neuroimaging abnormality (62.5%). Among the NPRL3 gene mutations, loss of function (nonsense mutations, frameshift mutations, and exons deletion) was the most common genetic variation (75%). For 73% of patients with NPRL3-related epilepsy, monotherapy of sodium channel blockers was effective. Surgery was effective for 75% of children with neuroimaging abnormalities. Two cases unresponsive to surgery or anti-seizure medications were treated with ketogenic diets (KD), which were effective. One case was treated with rapamycin at an early stage of epilepsy, which was effective as well.

Conclusion

NPRL3-related epilepsy has high clinical and genetic heterogeneity. SHE and FLE are the most common clinical presentations. Furthermore, ISs are the new phenotypes of NPRL3-related epilepsy, while the variants c.275G>A, c.745G>A, and c.1270C>T may be the most common NPRL3 gene mutations. Sodium channel blockers, surgery, KD, and rapamycin may be the potential treatments for these patients. Our study expanded the clinical and genetic spectrum of NPRL3-related epilepsy and provided important information for the precise treatment of patients.