Developmental and Epileptic Encephalopathies: Need for Bridging the Gaps Between Clinical Syndromes and Underlying Genetic Etiologies

Advancement in genetic testing has become increasingly important in diagnosing and managing developmental and epileptic encephalopathies (DEEs), a group of rare neurodevelopmental disorders characterized by early-onset seizures, developmental delay, and electroencephalographic (EEG) abnormalities. These early epileptic encephalopathies are often described as various syndromes as per their clearly defined, relatively uniform, and distinct clinical phenotypes with consistent EEG and/or neuroimaging findings. Finding the underlying molecular mechanisms can cause a definitive change in the management strategy. With the evolving overlapping phenotypes, advent of technologies, and discovery of new genes, it is exceedingly becoming challenging to correctly characterise these disorders and plan subsequent evidence-based management. Cytogenetic microarray (CMA) and next generation sequencing (NGS) with improved data analysis pipe-lines and algorithms have revamped the diagnostic yield dramatically. However, as of now, there is a big lacuna in step-wise evaluation guideline or consensus on integration of genetic testing results with management plan. Understanding the genetic etiologies of such syndromes timely has three major implications: (1) Knowing the outcome of such a syndrome, (2) Therapeutic implications including licensing of drugs for certain forms (e.g. genetic syndromes involving ion channels) and (3) Genetic counseling, prenatal testing and choosing reproductive options in future pregnancies in such families. The focus of this review is to provide an understanding of different types of causative variants and their step-wise genetic testing approach; the most pressing clinical need and to develop an optimal diagnostic pathway for this group of patients.