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PubMed This is a summary of 8 peer-reviewed journal articles Updated
Pediatric Neurology · Developmental and Epileptic Encephalopathy 85

Understanding Your Child's DEE85 Diagnosis

At a Glance

DEE85 is a rare condition caused by changes in the SMC1A gene. It usually causes seizures beginning in infancy and global developmental delay; some children also have developmental regression, smaller head growth after birth, or brain and heart differences, so care is coordinated across specialists.

Receiving a diagnosis of Developmental and Epileptic Encephalopathy 85 (DEE85) is a significant and often overwhelming moment. This condition is exceptionally rare, and it is common for local pediatricians or even general neurologists to have limited experience with it [1].

DEE85 is caused by changes (variants) in the SMC1A gene [1]. This gene provides instructions for a protein that is part of the cohesin complex, a group of proteins that helps organize the structure of chromosomes and regulates how genes are “turned on” or “off” during brain development [2][3]. When this gene does not function correctly, it disrupts the normal development and electrical activity of the brain.

The Typical Clinical Course

DEE85 is primarily defined by the intersection of severe epilepsy and developmental challenges. While every child’s journey is unique, research has identified several common features:

  • Early-Onset Seizures: In most children, seizures begin within the first year of life [1]. These seizures are often drug-resistant (refractory), meaning they may not respond fully to the first or second antiseizure medications tried [1].
  • Developmental Trajectory: Children typically experience global developmental delay, affecting both physical movement (motor skills) and cognitive abilities [1]. Some families may notice a regression, where a child loses previously gained skills, particularly after a period of intense seizure activity [1].
  • Growth Patterns: Many children with DEE85 have normal growth before birth but develop postnatal microcephaly (a smaller-than-expected head size) as they grow [1].
  • Organ Involvement: Beyond the brain, about 20% of children in a large international study were found to have cardiovascular (heart) malformations [1].

Understanding Brain Structure

While the primary challenges in DEE85 relate to brain function and seizures, structural changes can also occur. About 20% of children with this diagnosis have central nervous system (CNS) malformations [1]. These can include structural differences in the brain. However, it is important to note that the majority of children with DEE85 do not have these structural findings on an MRI [1].

DEE85 vs. Cornelia de Lange Syndrome (CdLS)

You may encounter information about Cornelia de Lange Syndrome (CdLS) during your research, as it is also linked to the SMC1A gene. While they share a genetic root, they are distinct conditions:

Feature DEE85 CdLS (SMC1A-related)
Primary Concern Severe, early-onset epilepsy [1] Growth and limb differences [3]
Genetic Mechanism Often “loss-of-function” variants [3] Often “dominant-negative” variants [3]
Epilepsy Central and typically drug-resistant [1] Less common and usually less severe [4]
Appearance Variable; no specific facial “look” [1] Distinctive facial features and limb issues [5]

In DEE85, the genetic change frequently results in a loss of the protein’s function, which has a more profound impact on brain stability and electrical activity [3]. However, variant type alone does not perfectly predict outcome, and overlapping features can occur.

Genetic Counseling

A crucial step is genetic counseling. A counselor can help you understand if the variant is “pathogenic” or just a “variant of uncertain significance”, whether it was de novo (a new mutation) or inherited, and if parents should be tested for mosaicism.

Managing the Path Ahead

Because DEE85 affects multiple systems, care usually requires a multidisciplinary team including neurologists, geneticists, and developmental therapists [1][6]. While the seizures can be difficult to manage, doctors may explore various treatments, including specialized diets like the ketogenic diet, though its effectiveness varies significantly between individuals [1][7].

The focus of care is often on “whole-child” support—balancing seizure control with therapies that promote communication, movement, and comfort [8]. Even in the face of a complex diagnosis, understanding the genetic “why” is a vital first step in finding the right specialists and community for your child.

Common questions in this guide

What causes DEE85 in a child?
DEE85 is caused by a change, or variant, in the SMC1A gene. SMC1A helps organize chromosomes and regulate genes during brain development, so variants can disrupt brain development and electrical activity. The change may be new in the child or inherited, and parental testing can be discussed with a genetic counselor.
When do DEE85 seizures usually start?
DEE85 seizures commonly begin during the first year of life. They may be drug-resistant, meaning they do not respond fully to initial antiseizure medicines. A pediatric neurologist may consider different medicines or a ketogenic diet, but treatment response varies between children.
Do all children with DEE85 have brain abnormalities on an MRI?
No. In a large international study, about 20% of children with DEE85 had central nervous system malformations, so most did not have these structural findings on MRI. The care team decides whether brain imaging or other screening is appropriate for an individual child.
How does DEE85 differ from SMC1A-related Cornelia de Lange syndrome?
DEE85 is primarily marked by severe, early-onset epilepsy and developmental challenges. SMC1A-related Cornelia de Lange syndrome more often involves growth, limb, and distinctive facial differences, while epilepsy is less common and usually less severe. Some features can overlap, so genetic and clinical evaluation are important.
Should parents be tested after a DEE85 diagnosis?
A genetic counselor can review whether the SMC1A variant is pathogenic or uncertain and whether it is new in the child or inherited. Testing both parents may help clarify recurrence risk and identify mosaicism when appropriate.
What kind of care does a child with DEE85 need?
Care often involves pediatric neurology, medical genetics, and developmental therapies. Treatment may include antiseizure medicines, a ketogenic diet in selected cases, and therapies supporting communication, movement, and comfort. The team may also discuss baseline heart screening because cardiovascular malformations have been reported.

Questions For You

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Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does my child's specific variant (such as a loss-of-function vs. missense variant) provide any clues about their expected seizure severity or developmental path?
  2. 2.Have you reviewed our genetic testing results to determine if this was a de novo (new) mutation, and should we as parents be tested?
  3. 3.What is the best way to monitor my child for potential developmental regression, and what therapies should we initiate now?
  4. 4.Based on findings in DEE85 cohorts, what baseline screenings (such as an echocardiogram) do you recommend for my child?
  5. 5.Can you explain how our child's presentation of DEE85 differs from the typical features of Cornelia de Lange Syndrome (CdLS)?

References

References (8)
  1. 1

    SMC1A epilepsy syndrome: clinical data from a large international cohort.

    Gibellato E, Cianci P, Mariani M, et al.

    American journal of medical genetics. Part A 2024; (194(7)):e63577 doi:10.1002/ajmg.a.63577.

    PMID: 38421079
  2. 2

    Linking Genotype to Clinical Features in SMC1A-Related Phenotypes: From Cornelia de Lange Syndrome to Developmental and Epileptic Encephalopathy, a Comprehensive Review.

    Astorino MF, Speranza D, Luppino G, et al.

    Genes 2025; (16(10)) doi:10.3390/genes16101196.

    PMID: 41153413
  3. 3

    Phenotypes and Genotypes in Patients with SMC1A-Related Developmental and Epileptic Encephalopathy.

    Bozarth XL, Lopez J, Fang H, et al.

    Genes 2023; (14(4)) doi:10.3390/genes14040852.

    PMID: 37107610
  4. 4

    Phenotypes and genotypes in individuals with SMC1A variants.

    Huisman S, Mulder PA, Redeker E, et al.

    American journal of medical genetics. Part A 2017; (173(8)):2108-2125 doi:10.1002/ajmg.a.38279.

    PMID: 28548707
  5. 5

    Further Characterization of SMC1A Loss of Function Epilepsy Distinct From Cornelia de Lange Syndrome.

    Barañano KW, Kimball A, Fong SL, et al.

    Journal of child neurology 2022; (37(5)):390-396 doi:10.1177/08830738221081244.

    PMID: 35238682
  6. 6

    The expanding field of genetic developmental and epileptic encephalopathies: current understanding and future perspectives.

    Specchio N, Trivisano M, Aronica E, et al.

    The Lancet. Child & adolescent health 2024; (8(11)):821-834 doi:10.1016/S2352-4642(24)00196-2.

    PMID: 39419567
  7. 7

    Phenotypic spectrum and long-term outcome of children with genetic early-infantile-onset developmental and epileptic encephalopathy.

    Hu C, Liu D, Luo T, et al.

    Epileptic disorders : international epilepsy journal with videotape 2022; (24(2)):343-352 doi:10.1684/epd.2021.1394.

    PMID: 34859793
  8. 8

    Deciphering the concepts behind "Epileptic encephalopathy" and "Developmental and epileptic encephalopathy".

    Scheffer IE, Liao J

    European journal of paediatric neurology : EJPN : official journal of the European Paediatric Neurology Society 2020; (24()):11-14 doi:10.1016/j.ejpn.2019.12.023.

    PMID: 31926847

This explanation of DEE85 is for informational purposes only and does not constitute medical advice. Your child's pediatric neurologist, geneticist, and developmental team should interpret genetic results and tailor screenings and treatment.