Developmental and Epileptic Encephalopathy 85 (DEE85): A Patient Guide

Developmental and Epileptic Encephalopathy 85 (DEE85) is a rare, X-linked genetic condition that fundamentally alters the brain’s electrical stability and developmental path. It is caused by variants in the SMC1A gene, which provides instructions for a protein that helps organize the structure of DNA ^[1][2]. Because this gene is critical for the proper “folding” of genetic material and the regulation of other genes, a variant can lead to significant disruptions in how the brain develops and functions. This condition is primarily diagnosed in females. While severe loss-of-function variants are often presumed lethal in males during early development, male cases can occur depending on the specific genetic variant and whether mosaicism (where only some cells carry the variant) is present ^[3].

The clinical journey of DEE85 often begins in infancy, typically within the first year of life, with the onset of severe and often drug-resistant (refractory) seizures ^[1]. These seizures do not occur in isolation; they are part of a broader “encephalopathy,” meaning the intense electrical activity itself—along with the underlying genetic change, medication side effects, and sleep disruption—can interfere with a child’s ability to learn and grow ^[1]. While a baby may meet early milestones, the onset of epilepsy is frequently followed by developmental regression, where previously acquired skills are lost, and postnatal microcephaly, a slowing of head growth relative to the rest of the body ^[1]. Although DEE85 shares the same gene with Cornelia de Lange Syndrome (CdLS), it is a distinct clinical entity defined by its early, severe epilepsy and different genetic mechanisms ^[3].

Living with DEE85 requires a holistic, multidisciplinary approach to care that looks beyond the brain. In a large international cohort study, approximately 20% of children with this diagnosis had structural differences in the heart or the central nervous system, and about half experienced neonatal challenges, which included a mix of early seizures and respiratory issues ^[1]. Because every child’s genetic variant and clinical presentation are unique, care teams usually include specialists in neurology, genetics, cardiology, and various therapies to manage these complex needs. While the medical journey is undoubtedly challenging, the primary focus of modern care is to maximize each child’s quality of life through tailored seizure management, communication support, and motor therapies that honor their individual potential ^[4][5].