Characteristics of Genetic Variations Associated With Lennox-Gastaut Syndrome in Korean Families

Abstract

Lennox-Gastaut syndrome (LGS) is a severe type of childhood-onset epilepsy characterized by multiple types of seizures, specific discharges on electroencephalography, and intellectual disability. Most patients with LGS do not respond well to drug treatment and show poor long-term prognosis. Approximately 30% of patients without brain abnormalities have unidentifiable causes. Therefore, accurate diagnosis and treatment of LGS remain challenging. To identify causative mutations of LGS, we analyzed the whole-exome sequencing data of 17 unrelated Korean families, including patients with LGS and LGS-like epilepsy without brain abnormalities, using the Genome Analysis Toolkit. We identified 14 mutations in 14 genes as causes of LGS or LGS-like epilepsy. 64 percent of the identified genes were reported as LGS or epilepsy-related genes. Many of these variations were novel and considered as pathogenic or likely pathogenic. Network analysis was performed to classify the identified genes into two network clusters: neuronal signal transmission or neuronal development. Additionally, knockdown of two candidate genes with insufficient evidence of neuronal functions, SLC25A39 and TBC1D8, decreased neurite outgrowth and the expression level of MAP2, a neuronal marker. These results expand the spectrum of genetic variations and may aid the diagnosis and management of individuals with LGS.

Keywords: Lennox-Gastaut syndrome; Rare-diseases; epilepsy; genetic variation; whole-exome sequencing.

FIGURE 1

Workflow for identifying potential causative genetic variants related to LGS or LGS-like epilepsy.

FIGURE 2

Pedigree of LGS or LGS-like epilepsy families. Males and females are represented as squares and circles, respectively. Patients with LGS are indicated as completely filled symbols, and those with LGS-like epilepsy are indicated as half-filled symbols. The circle with dots indicates females with mild intellectual disabilities.

FIGURE 3

Statistics of genetic variations in candidate genes of LGS or LGS-like epilepsy. (A) Pie chart of the frequency of LGS, epilepsy, or neuron-related genes. () indicates the number of genetic variations in candidate genes. (B) Ratio of Mendelian inheritance patterns of candidate genes.

FIGURE 4

Ingenuity Pathway Analysis (IPA) results for candidate genes of LGS or LGS-like epilepsy. The genes with cyan or orange colors indicate candidate genes selected in this study. The genes with yellow color represent those most relevant to the candidate genes. (A) Cell signaling network. (B) Neurological disease network.

FIGURE 5

Neurite length analysis by knockdown of candidate genes in neuronal cells. Human SH-SY5Y neuroblastoma cells were transfected with siRNA for TBC1D8 and SLC25A39 on day 3 in vitro (DIV 3). MAP2 was used as a neuronal marker. (A) Expression levels of TBC1D8, SLC25A39, and MAP2 were analyzed by RT-PCR (n = 3). (B) After retinoic acid stimulation for 48 h, the cells were stained for MAP2 (green) and nuclei (blue). Scale bars: 30 μm. (C) Neurite length was measured in more than 10 cells in three independent experiments. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, and Student’s t-test compared with the control group.