Objectives: The developmental and epileptic encephalopathies (DEE) are a heterogeneous group of rare neurodevelopmental disorders, characterised by early-onset seizures that are often intractable, electroencephalographic abnormalities, and developmental delay or regression. There is a paucity of data from sub-Saharan Africa on the genetic basis of DEE. The aim of this study was to investigate the genetic background of DEE using targeted next generation sequencing (NGS) analysis in a tertiary pediatric neurology outpatient department at Tygerberg Hospital, South Africa. In addition, we assessed the value of the genetic results to the parents and managing physicians.
Methods: A prospective cohort study of 41 consecutive children with DEE (onset before 3 years of age) that were recruited over a 2-year period (2019-2021). Pre- and post-test genetic counselling were offered to all study participants. The results were categorized as either: positive (pathogenic/likely pathogenic variant identified), inconclusive (variant(s) of unknown significance identified), or negative (no variants identified). Result interpretation and careful matching of the variant to the clinical phenotype was performed. Subsequently, questionnaires were administered to both the physicians and the parents.
Results: A genetic underlying cause for DEE was identified in 18 of 41 children (diagnostic yield 43.9%). Variants in SCN1A (n=7), KANSL1 (n=2), KCNQ2 (n=2) and CDKL5 (n=2) were identified in more than one patient. Rarer genes included IQSEC2, SMC1A and STXBP1. All of the identified pathogenic variants fully explained and matched the respective phenotypic description of the patient at the time of clinical diagnosis. In 26% of patients the genetic result facilitated precision medicine management changes to anti-seizure medication. Both parents and physicians expressed benefit of genetic testing in patients with DEE.
Conclusion: Targeted NGS analysis proved an efficient diagnostic tool in detection of a genetic cause of DEE in a large proportion of South African children. The 43.9% diagnostic yield is similar to previously reported international pediatric cohorts. Additionally, the genetic findings proved useful for targeted therapeutic decision-making and accurate genetic counseling.
Keywords: Developmental and epileptic encephalopathies; Epilepsy; Genomics; Next generation sequencing; Sub-Saharan Africa.
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