What families and clinicians need to know about a rare Notch-pathway disorder of brain development — the gene, the diagnoses it causes, the science, and the path to answers.
A small gene at the end of chromosome 6 produces a molecular handshake between developing brain cells. When that handshake breaks down — even a little — a child's entire neurological development can change course.
DLL1 United was founded by a mother whose five-year-old son was diagnosed with a rare disorder of the gene DLL1. Like many families on this path, we spent years navigating a medical system that could name our son's individual symptoms but could not name the cause. When the diagnosis finally came, so did community, clarity, and a roadmap. This page is for the families and clinicians still searching.
DLL1 encodes Delta-like Canonical Notch Ligand 1 — a critical signaling molecule for brain morphogenesis. Variants in DLL1 cause a spectrum of conditions ranging from a dominant neurodevelopmental disorder (NEDBAS) to a rare recessive skeletal syndrome (SCDO7) to larger chromosomal deletions of 6q27. The clinical picture varies, but the underlying biology is shared: a disrupted Notch pathway during the windows of life when the brain and spine are built.
DLL1 sits at the very end of chromosome 6, in a region called 6q27. It is one of the smaller genes in the human genome — just 11 exons spanning roughly 16,000 letters of DNA — but it produces a protein with outsized influence over how the brain and spine are built.
The protein it encodes, Delta-like Canonical Notch Ligand 1, is a 723-amino-acid transmembrane molecule. It sits on the surface of one cell and binds NOTCH receptors on neighbouring cells. That contact triggers a cascade — including release of the Notch intracellular domain (NICD) and changes in gene expression — that decides what each cell will become.
Notch signalling decides whether a cell becomes a neuron or a support cell, when neural progenitors divide vs. differentiate, and how the spinal column segments. When DLL1 dose drops, those decisions are mistimed — and the consequences are wide-ranging.
Variants in DLL1 produce three clinically distinguishable patterns depending on how the gene is disrupted: a dominant form with prominent neurodevelopmental features, a rare recessive form with skeletal features, and chromosomal deletions that remove the entire gene along with its neighbours. All three share Notch-pathway biology — the differences come from dose, mechanism, and what surrounding DNA is also affected.
Neurodevelopmental Disorder with Nonspecific Brain Abnormalities and With or Without Seizures. Caused by a single defective copy of DLL1 — either a new spontaneous mutation in the child, or inherited from an affected parent with variable severity.
An extremely rare skeletal form. Both copies of DLL1 carry the same missense variant c.1534G>A (p.Gly512Arg) in exon 9. Each parent carries one copy and is unaffected.
Larger chromosomal deletions of the 6q27 region remove DLL1 along with neighbouring genes. Phenotype severity correlates with deletion size and which other genes are lost.
The same gene can produce three quite different conditions. Knowing which form your child has — dominant, recessive, or chromosomal — shapes the questions you ask, the specialists you see, and the recurrence risk for future pregnancies.
The first description of DLL1-related neurodevelopmental disorder came in 2019, when Björn Fischer-Zirnsak and colleagues published a cohort of 15 individuals with heterozygous DLL1 variants and overlapping features of intellectual disability, autism, brain malformations, and seizures.
Since then, GeneMatcher and clinical sequencing have identified additional families across multiple continents. The condition received the OMIM designation NEDBAS — Neurodevelopmental Disorder with Nonspecific Brain Abnormalities and With or Without Seizures — and the molecular picture continues to expand.
DLL1-related conditions are ultra-rare. The numbers below reflect what has been published in the medical literature. The true prevalence is almost certainly higher — many people with DLL1 variants have not yet had genetic testing, or were tested before DLL1 was on standard panels.
Fischer-Zirnsak et al. 2019 (AJHG) — 15 individuals from 12 unrelated families established NEDBAS as a Mendelian condition.[1]
Combining the founding cohort with subsequent case reports identified through GeneMatcher and clinical sequencing.[2]
13 of 15 individuals in the founding cohort — severity ranged from mild to severe.[1]
Hydrocephalus, white-matter changes, cortical dysplasia, and microcephaly were the most common findings.[1]
Rarity does not mean isolation. Every additional diagnosed family contributes to a clearer picture of the condition — and to the leverage needed for natural-history studies, clinical guidelines, and one day, treatments.
DLL1-related conditions vary widely — even within the same family, two siblings carrying the same variant can present quite differently. Frequencies refer to the proportion of described patients who showed each feature; absence of a feature does not rule out the diagnosis.
DLL1 sits alongside DLL3 (spondylocostal dysostosis type 1), DLL4 (Adams-Oliver syndrome), JAG1 (Alagille syndrome), and NOTCH1–4 (cardiac, vascular, and developmental conditions). Despite shared biology, each disease has a distinct fingerprint — DLL1's signature is the combination of variable neurodevelopmental features with subtle skeletal findings.
DLL1 has conventional exonic structure — which means, unlike some recently-discovered rare-disease genes, it is reliably detected by standard whole exome sequencing. The diagnostic challenge with DLL1 is not visibility — it is awareness. The right test, ordered with the right intent and interpreted by someone familiar with the Notch pathway, will find a DLL1 variant if one is present.
| Test | Detects DLL1? | Notes |
|---|---|---|
| Whole Exome Sequencing (WES) | Yes — first line | Reliably detects DLL1 SNVs and small indels. Trio WES improves diagnostic yield. |
| Whole Genome Sequencing (WGS) | Yes | Adds structural variants, deep intronic changes, and 6q27 deletions in a single test. |
| Chromosomal Microarray (CMA) | Deletions only | Required to characterise 6q27 terminal deletions and co-deleted neighbours. |
| Karyotype | Large rearrangements only | Will not detect point mutations; useful only for visible chromosomal abnormalities. |
| ID / epilepsy gene panels | If DLL1 included | Confirm the panel content includes DLL1 — older panels may not. |
| Targeted DLL1 sequencing | Yes | Used for cascade testing of relatives once a family variant is known. |
Many DLL1 variants are still classified as VUS (variants of uncertain significance). If your child carries a VUS, it does not rule the diagnosis in or out — segregation analysis, functional studies, and re-classification over time are how the picture sharpens.
Ask your geneticist about trio whole exome sequencing as a first-line test. If WES has already been done and was reported as negative, ask whether DLL1 was specifically reviewed — it is sometimes missed when the indication does not flag the Notch pathway.
Last fact-checked: May 2026. This page is informational and is not medical advice.
If you are a family, clinician, or researcher touched by DLL1, we would like to hear from you. Every voice helps build a clearer map for the families still searching.