The Genetic Landscape of Epilepsy of Infancy with Migrating Focal Seizures

Abstract

Objective: Epilepsy of infancy with migrating focal seizures (EIMFS) is one of the most severe developmental and epileptic encephalopathies. We delineate the genetic causes and genotype-phenotype correlations of a large EIMFS cohort.

Methods: Phenotypic and molecular data were analyzed on patients recruited through an international collaborative study.

Results: We ascertained 135 patients from 128 unrelated families. Ninety-three of 135 (69%) had causative variants (42/55 previously reported) across 23 genes, including 9 novel EIMFS genes: de novo dominant GABRA1, GABRB1, ATP1A3; X-linked CDKL5, PIGA; and recessive ITPA, AIMP1, KARS, WWOX. The most frequently implicated genes were KCNT1 (36/135, 27%) and SCN2A (10/135, 7%). Mosaicism occurred in 2 probands (SCN2A, GABRB3) and 3 unaffected mothers (KCNT1). Median age at seizure onset was 4 weeks, with earlier onset in the SCN2A, KCNQ2, and BRAT1 groups. Epileptic spasms occurred in 22% patients. A total of 127 patients had severe to profound developmental impairment. All but 7 patients had ongoing seizures. Additional features included microcephaly, movement disorders, spasticity, and scoliosis. Mortality occurred in 33% at median age 2 years 7 months.

Interpretation: We identified a genetic cause in 69% of patients with EIMFS. We highlight the genetic heterogeneity of EIMFS with 9 newly implicated genes, bringing the total number to 33. Mosaicism was observed in probands and parents, carrying critical implications for recurrence risk. EIMFS pathophysiology involves diverse molecular processes from gene and protein regulation to ion channel function and solute trafficking. ANN NEUROL 2019;86:821-831.

Figure 1

The molecular genetic landscape of EIMFS. 69% of patients have an identified molecular cause: 50% patients have variants in genes that follow dominant inheritance (blue, most are de novo), rare patients have X-linked genes (green) and rare patients have variants following homozygous or compound heterozygous (brown) patterns. Bold gene names are genes newly associated with EIMFS. Numbers indicate the number of patients with a pathogenic variant in each gene in our cohort.

Figure 2

Inheritance patterns of pathogenic variants associated with EIMFS. Autosomal dominant, recessive, and X-linked inheritance may occur. Mosaicism should be considered in affected children as well as unaffected and affected parents. Lower levels of mosaicism are more likely to be present in unaffected individuals, while higher levels of mosaicism can occur with mildly or severely affected individuals.