A 2021 paper in Genes took a wide look at Kabuki Syndrome. Here’s our AI Summary - followed by an interesting assessment from ChatGPT about what has changed since then. - chrism
Kabuki syndrome has long been recognized by clinicians because of its distinctive facial features and characteristic pattern of developmental challenges. But over the last two decades, it has also become a model condition for understanding how subtle errors in gene regulation—rather than missing genes or broken proteins—can ripple across development. This review brings together what is known about Kabuki syndrome from both sides: the lived clinical reality and the molecular machinery underneath.
Rather than presenting new experiments, the authors take a wide-angle view, synthesizing clinical observations, genetic discoveries, and emerging biological insights into a single, coherent picture of the disorder.
Clinical Presentation: A Consistent Pattern with Wide Variation
The review begins with the clinical features that first brought Kabuki syndrome to medical attention. Most individuals share a recognizable facial appearance, including elongated eye openings, arched eyebrows, and large ears. These features are not merely cosmetic markers; they reflect shared developmental pathways affected early in embryogenesis.
Beyond facial characteristics, the syndrome includes a consistent—but variable—set of challenges:
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Developmental delay, particularly affecting motor skills and speech
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Low muscle tone (hypotonia)
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Postnatal growth delay and feeding difficulties
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Skeletal anomalies, including joint laxity and spinal differences
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Congenital heart defects and kidney anomalies in a subset of patients
Importantly, the authors emphasize variability. No two individuals with Kabuki syndrome present identically. Cognitive ability can range from mild learning difficulties to more significant intellectual disability, and medical complications differ widely. This variability becomes a key theme later, when genetics and gene regulation are discussed.
Genetics of Kabuki Syndrome: Two Core Genes, Many Paths
The molecular heart of Kabuki syndrome lies in two genes: KMT2D and KDM6A.
KMT2D
Variants in KMT2D account for roughly three-quarters of known Kabuki cases. Most are loss-of-function variants—changes in DNA that reduce or eliminate normal gene activity. These can include truncating variants or, in some cases, missense variants (a single-letter DNA change that swaps one amino acid for another in the protein).
KDM6A
KDM6A variants are less common and are inherited in an X-linked manner. Because of this, males often show more severe symptoms when affected, though females can also be impacted due to incomplete X-chromosome compensation.
The Unsolved Fraction
Crucially, the review highlights that around 20 % of clinically diagnosed individuals do not yet have an identified genetic cause. This is not a diagnostic failure, but rather a sign that Kabuki syndrome is genetically more complex than initially thought. Regulatory regions, deep intronic variants, or additional interacting genes may play a role—an idea that resonates strongly with current research directions.
What These Genes Do: Controlling Gene Expression, Not Making Parts
A central contribution of this review is its explanation of why mutations in KMT2D and KDM6A have such broad effects.
Neither gene builds a structural component of the body. Instead, both are involved in epigenetic regulation—the system cells use to decide which genes are turned on or off, and when.
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Histones are proteins around which DNA is wrapped. Chemical tags on histones help control access to genes.
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KMT2D normally adds activating marks to histones, helping open DNA so genes needed for development can be expressed.
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KDM6A removes repressive marks, allowing gene activation to proceed.
When either process is disrupted, the timing and level of gene expression during embryonic development can shift. The review frames Kabuki syndrome not as a disorder of missing instructions, but as a disorder of mis-timed and mis-regulated instructions.
Insights from Model Systems
To understand these mechanisms, researchers have relied heavily on mouse models—genetically engineered mice that carry changes in Kmt2d or Kdm6a.
These models recapitulate many Kabuki-like features, including growth delays, craniofacial differences, and learning deficits. Importantly, they also show that many abnormalities arise early in development, before birth.
The review uses these findings to reinforce a key idea: Kabuki syndrome is fundamentally a neurodevelopmental and developmental-patterning disorder, not simply a postnatal learning condition.
Neurological and Cognitive Features
The authors devote significant attention to the brain and nervous system. Individuals with Kabuki syndrome often show:
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Delayed motor milestones
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Speech and language delays
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Difficulties with attention and executive function
Mouse studies suggest that altered gene regulation affects neuronal maturation, synapse formation, and circuit refinement. Rather than causing neuron loss, the disorder appears to alter how neural networks are assembled and tuned.
This framing helps explain why learning profiles in Kabuki can be uneven—strong memory or verbal skills alongside challenges in spatial reasoning or planning.
Immune, Endocrine, and Metabolic Findings
Kabuki syndrome does not stop at the brain. The review includes detailed sections on other organ systems:
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Immune system: Increased susceptibility to infections and immune dysregulation in some patients
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Endocrine system: Growth hormone deficiency, delayed puberty, and metabolic differences
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Gastrointestinal system: Feeding difficulties and structural anomalies
The unifying idea is that epigenetic regulators like KMT2D influence many developmental programs. Disruption in one regulatory hub can therefore produce a multi-system condition.
Diagnosis and Clinical Management
From a clinical standpoint, the review underscores the growing role of genetic sequencing. Diagnosis typically begins with clinical suspicion, followed by confirmatory testing using next-generation sequencing panels or whole-exome sequencing.
Management remains supportive and multidisciplinary, involving developmental therapies, cardiac and renal monitoring, endocrine care, and educational supports. There is currently no curative treatment, a point the authors state clearly and without speculation.
What This Review Makes Clear—and What It Leaves Open
This paper’s strength lies in integration. It shows how a consistent clinical syndrome emerges from disruptions in gene regulation and how early developmental timing shapes lifelong outcomes.
At the same time, it leaves important questions unresolved:
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What explains the full genetic diversity of Kabuki syndrome?
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How reversible are epigenetic disruptions once development is complete?
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Which symptoms are most sensitive to future therapeutic intervention?
still with us (me+chatgpt)? After generating this, ChatGPT proposed we take a look at what’s changed since 2021. I said yes! here’s what it came up with. - chris m.
What’s changed since 2021
Boniel et al.’s 2021 Genes review is a great “spine” for Kabuki because it organizes the syndrome the way families experience it—multi-system, variable, and developmental—then ties that to KMT2D/KDM6A as master regulators of how cells turn genes on and off (via chromatin and histones, the DNA-packaging proteins).
What’s changed since 2021 is that the field has gotten much better at answering a practical follow-up question: “Okay, but which cells, which developmental windows, and which gene programs are most affected—and can we measure that in human-derived systems?” That evolution has largely come from three toolkits: iPSCs, single-cell profiling, and enhancer-focused epigenomics.
From “two genes” to “which regulatory programs break”
The 2021 review emphasizes that KMT2D and KDM6A are not “single pathway” genes—they sit upstream of many developmental programs, which helps explain Kabuki’s broad symptom range.
Post-2021 work has sharpened that idea into something more testable: Kabuki (especially KS1, KMT2D) often looks like a disorder of enhancer regulation. Enhancers are stretches of DNA that act like dimmer switches for genes, especially during development. Mechanistically, KMT2D helps place enhancer-associated histone marks (commonly H3K4me1/H3K4me2), so “what breaks” can be read out as a signature of weakened or mis-timed enhancers.
A good example is a large human study using immune cells (PBMCs) from people with KMT2D variants: it reported distinct enhancer signatures—including reduced enhancer-associated histone signals—alongside transcriptional changes. That’s important not because blood is “the disease tissue,” but because it demonstrates a measurable, variant-linked epigenomic fingerprint in human samples.
iPSCs: recreating early development (and seeing timing problems)
The biggest leap since 2021 is the routine use of iPSCs (induced pluripotent stem cells)—adult cells (often skin or blood) reprogrammed back into a stem-like state—then pushed forward into neuronal progenitors and neurons. This lets researchers observe developmental timing in a dish.
A 2025 study followed KS1 patient-derived iPSCs across three stages (iPSC → neuronal progenitor → early cortical neuron) and measured both gene expression and histone marks. The headline result is strikingly “Kabuki-appropriate”: widespread loss of enhancer-associated marks (notably H3K4me1) appeared across stages, paired with coordinated transcriptional shifts during neuronal differentiation. In other words, the regulatory “dimmer switches” look globally altered as cells try to become neurons.
That kind of work directly extends the 2021 review’s core claim—Kabuki is about gene regulation—by showing whenand how consistently the regulatory landscape diverges during neurodevelopment in human-derived cells.
Single-cell and “multi-modal” profiling: not just what changes, but which cells change
The review format in 2021 necessarily talks about Kabuki at the level of organs and syndromes. Newer methods let the field ask: within a mixed population of developing cells, which subtypes are most altered?
Two trends stand out:
1) Single-cell RNA-seq (scRNA-seq):
scRNA-seq measures gene activity one cell at a time, revealing whether a change is “everyone shifts a little” versus “a specific subpopulation shifts a lot.” A 2024 study using scRNA-seq in Kabuki reported dysregulated programs related to ribosomal/translation processes and explored dietary modulation effects—an example of how single-cell readouts are being used to connect molecular signatures to intervention hypotheses (still early, but methodologically important).
2) Multi-modal phenotyping (morphology + transcriptome):
An especially “post-2021” move is combining scRNA-seq with cell imaging phenotypes like Cell Painting (a standardized, high-content microscopy assay that stains multiple cell structures to quantify cell shape/state). A 2025 eLife study (which we covered here on Kabuki Brain - ed) applied this multi-modal approach and then tested it on iPSC-derived neural progenitors from Kabuki patients, finding morphological signatures consistent with precocious differentiation and altered cycling—phenotypes that connect nicely to older ideas that KMT2D disruption can push cells out of the proliferative state too early.
Put simply: since 2021, Kabuki research has gotten better at saying “this specific developmental trajectory looks accelerated or mis-routed,” not just “development is abnormal.”
Organoids and neural crest: getting closer to “cell-of-origin” questions
The 2021 review stresses multi-system involvement (craniofacial, cardiac, immune, neurodevelopmental). One reason Kabuki is so multi-system is that KMT2D/KDM6A influence early lineages like neural crest (a transient embryonic cell population that contributes to facial structures, parts of the heart, peripheral nerves, etc.).
Post-2021, organoid models—3D “mini-tissues” grown from stem cells—have become a way to study these lineage choices. A 2024 paper optimized a brain organoid model to examine neural crest and neuronal differentiation under KMT2D/KDM6A disruption, explicitly targeting the “impacted cell-of-origin” question in development.
This matters because it helps bridge symptoms that families see (craniofacial differences + neurodevelopmental profile) with a plausible shared developmental substrate (lineage decisions and maturation timing in neural crest–related and neuronal pathways).
Where enhancer biology is heading next
The 2021 review notes that a meaningful fraction of clinically diagnosed Kabuki cases don’t yet have a confirmed molecular diagnosis. Since then, the enhancer story has made one prediction feel increasingly plausible: some “missing” cases may involve noncoding/regulatory variants (introns, enhancers, structural variants) that are harder to detect and interpret than classic coding mutations. Case reports of intronic KMT2D variants exist, and the technical momentum in the field (long-read sequencing + enhancer maps) is pushing toward better discovery and interpretation of these regulatory changes.
What’s still hard—and where the field is actively working—is turning “enhancer disruption” into a precise, patient-level statement like: “this enhancer affects this developmental program in this lineage at this time.” The newer iPSC, organoid, and single-cell toolkits are basically the measurement scaffolding needed to get there.
What this evolution changes for families (and what it doesn’t—yet)
A helpful way to summarize the post-2021 shift is:
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Then (2021): “Kabuki is a recognizable syndrome caused mainly by KMT2D/KDM6A, which affect chromatin and gene regulation across development.”
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Now: “We can measure the downstream regulatory disruption in human-derived developmental models, often as enhancer/histone-mark changes plus altered maturation timing—and we can localize it to particular cell states using single-cell methods.”
What this doesn’t automatically mean is “a therapy is imminent.” These studies are still mostly about mechanism and measurement—but that’s exactly what you need before rational therapies can be evaluated in a way that’s more than guesswork.