Epigenetics
179 Syndromes, One Family: The case for studying Kabuki as a Chromatinopathy
A sweeping new review argues that Kabuki syndrome shares deep molecular roots with 178 other epigenetic disorders — and that breakthroughs in any one of them, from episignature diagnostics to CRISPR-based therapies, could benefit them all.
What if Kabuki syndrome is best understood not on its own, but as part of a much larger family of conditions? A new review maps out that family—called chromatinopathies—and argues that seeing the bigger picture could accelerate diagnosis, monitoring, and eventually treatment for all of them.
Chromatinopathies (CPs) are rare disorders caused by mutations in genes that regulate the epigenome—the molecular machinery that controls when and where our genes turn on or off. There are now 179 recognized CP syndromes, and Kabuki syndrome is one of them.
The review pulls together what's known about CPs as a class: their shared clinical features, their unique DNA methylation fingerprints, and the emerging therapies that might one day target them. For Kabuki families, it's a useful lens—because advances in any one CP may ripple across the group.
What are chromatinopathies?
The term was originally coined for conditions resembling Cornelia de Lange syndrome but caused by different genes. It has since expanded dramatically. Today, CPs refer to any developmental disorder caused by germline mutations in so-called "epigenes"—genes encoding proteins that maintain the epigenome.
These proteins come in many flavors. An early classification sorted them into four groups: chromatin modifiers, chromatin remodelers, proteins that modify DNA or RNA, and accessory proteins. A more recent scheme lists 17 categories, including histone writers (enzymes that add chemical tags to histones—the proteins DNA wraps around), histone erasers (which remove those tags), histone readers, chromatin remodelers, and many types of cofactors.
Thanks to next-generation sequencing (NGS)—high-throughput methods for reading DNA—researchers have now linked 154 of roughly 300 known epigenes to specific CP syndromes.
What CPs have in common
Despite their genetic diversity, CPs share a recognizable clinical profile. Common features include neurodevelopmental delay, intellectual disability, seizures, facial differences, growth and feeding difficulties, and heart or skeletal abnormalities. Symptoms often change over time, making long-term monitoring essential.
Beyond these core features, individuals with CPs may face immunodeficiency and an increased predisposition to cancer. Early detection of heart defects, malignancy, and immune problems is critical.
Heart defects across CPs
Congenital heart defects span a wide range across CP syndromes, including tetralogy of Fallot, atrial and ventricular septal defects, interrupted aortic arch, pulmonary and aortic stenosis, patent ductus arteriosus, mitral valve anomalies, and double-outlet right ventricle. These defects can be overshadowed by other features of the underlying syndrome, leading to under-recognition and inadequate treatment. The review stresses that electrocardiography and echocardiography should be performed at genetic diagnosis and repeated during follow-up.
Immune vulnerability—including in Kabuki
Epigenes involved in CPs also play roles in immune function, making thorough immunological workup essential.
In Kabuki syndrome specifically, mutations in KMT2D and KDM6A impair B-lymphocyte terminal differentiation—the final step in which immune cells mature into antibody-producing machines. This leads to hypogammaglobulinemia (low antibody levels), reduced memory B cells, and common variable immunodeficiency (CVID).
Other CPs carry their own immune signatures. Cornelia de Lange syndrome patients frequently battle chronic ear infections, pneumonia, oral candidiasis, sepsis, and bacterial skin infections. CHARGE syndrome can cause immune defects ranging from mild T-cell changes to severe combined immunodeficiency (SCID). In Kleefstra syndrome, pulmonary infections tend to be more severe in patients with larger chromosomal deletions. And Rubinstein-Taybi syndrome can present with B-cell defects, T-cell defects, autoimmunity, or SCID.
Cancer risk
Some CPs carry a meaningful cancer risk—and not only the ones already known for it. Kabuki syndrome has been linked to hematological malignancies including acute lymphocytic leukemia, Hodgkin's lymphoma, and Burkitt lymphoma, as well as solid tumors such as giant cell fibroblastoma.
Cornelia de Lange syndrome patients most commonly develop esophageal cancer, though leukemia, gastric cancer, and Wilms tumor have also been reported. Coffin-Siris syndrome has been associated with medulloblastoma, neuroblastoma, hepatoblastoma, and acute lymphoblastic leukemia, among others. Rubinstein-Taybi syndrome carries a particularly long list of associated cancers and an increased risk of benign meningiomas and pilomatricoma.
Episignatures: a molecular fingerprint
One of the most promising developments in the CP field is the discovery of episignatures—distinctive DNA methylation patterns specific to particular gene variants. These patterns differ reliably between CP patients and healthy controls.
DNA methylation (the addition of a small chemical tag—a methyl group—to cytosine bases in DNA) is a fundamental way cells control which genes are active. It varies across cell types and changes over the life of a cell. When the proteins that maintain the epigenome are disrupted by CP-causing mutations, the result is aberrant methylation signatures and broader epigenome destabilization.
The first genome-wide episignature was reported in 2013, for a condition caused by variants in the gene KDM5C. Since then, episignatures have been described for over 90 conditions. All known disease-associated episignatures are cataloged in a free online resource called EpigenCentral.
These fingerprints are turning out to be powerful diagnostic tools. They can distinguish affected from unaffected individuals, differentiate disease-causing from benign variants, and help evaluate variants of unknown significance (VUS)—genetic changes whose clinical meaning is unclear. They've even been applied to detect mosaic variants (where only some of a patient's cells carry the mutation), including low-level mosaicism in the Kabuki-related genes KMT2D and KMT2C.
There's a practical catch, though. Some episignatures overlap when the affected genes encode proteins that work in the same molecular complex. This has been shown for KDM6A and KMT2D (both involved in Kabuki syndrome), as well as for genes in the polycomb repressive complexes.
Looking ahead, episignatures may also serve as biomarkers for monitoring treatment, if precision-targeted therapies can reverse the aberrant methylation patterns.
Current care and emerging therapies
Today, CP management centers on supportive care and preventive screening. Neurodevelopmental and behavioral symptoms can be managed with occupational therapy, physical therapy, speech and language therapy, behavioral therapy, and medications for ADHD, anxiety, or epilepsy. Screening should be routine for syndromes with higher risks of malignancy, cardiac defects, or immunodeficiency.
No FDA-approved targeted therapy for any CP exists yet. But the field is moving.
Epigenetic modification using small molecules is already well established in cancer. HDAC inhibitors (histone deacetylase inhibitors—drugs that block enzymes removing acetyl tags from histones) such as vorinostat, belinostat, romidepsin, tucidinostat, and panobinostat represent one approach. In a Rubinstein-Taybi syndrome mouse model (a lab mouse engineered to carry a human disease gene), HDAC inhibition reversed memory defects—a striking proof of concept.
Other strategies are further along in specific CPs. In Angelman syndrome, a topoisomerase inhibitor called topotecan reactivated the abnormally silenced gene in a mouse model. Antisense oligonucleotides (ASOs)—short synthetic DNA or RNA molecules that alter the expression of a target gene—are being broadly tested to restore UBE3A expression in Angelman neurons. ASOs work by blocking or inactivating Ube3a-ATS, a long non-coding antisense RNA that normally silences the paternal copy of Ube3a. Four active phase 1/2a clinical trials are underway using various ASO designs. Similar rescue has been achieved in the lab with CRISPR/Cas9 genome editing and CRISPR-mediated RNA editing.
In Prader-Willi syndrome, inhibitors of the enzyme EHMT2/G9a—which reduce a repressive histone mark called H3K9me2—successfully unsilenced normally repressed candidate genes in a mouse model. DNA methylation and demethylation approaches are also being applied to imprinting disorders like Beckwith-Wiedemann syndrome.
Perhaps the most flexible emerging tool is CRISPR/Cas9-mediated epigenome editing, which enables targeted manipulation of histone modifications and gene expression without changing the underlying DNA sequence.
The applicability of these epigenome-targeting approaches extends well beyond CPs into a broad spectrum of diseases. Given the pace of advancement, the review's authors consider it highly probable that targeted CP therapies will eventually reach the clinic.
The bigger picture
The epigenome regulates chromatin state—whether DNA is tightly packed and silent, or open and active—through DNA methylation and posttranslational modifications of histones (chemical changes made after a protein is produced), including methylation, acetylation, phosphorylation, and ubiquitination. These modifications form a "histone code" that governs chromatin structure, histone-DNA interactions, and the recruitment of regulatory proteins. They work through two main mechanisms: neutralizing the electrical charge on nucleosomes (as acetylation does, loosening DNA's grip on histones) and recruiting chromatin-remodeling proteins to specific tagged sites.
DNA methylation and histone marks don't operate independently. The repressive histone mark H3K9me3 and CpG methylation tend to co-occur and reinforce each other, while DNA methylation and the activating mark H3K4me3 are mutually exclusive. Heterochromatin (tightly packed DNA) is hypermethylated and transcriptionally silent; euchromatin (open DNA) is hypomethylated and permissive.
DNA methylation is catalyzed by enzymes called DNA methyltransferases (DNMTs), and dysregulation of these enzymes can lead to the abnormal methylation patterns seen in CPs and cancer. Multiple forms of DNA methylation exist—5-methylcytosine (5mC) is the most common, but 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxylcytosine have also been identified. Methylation levels are highest in repeated elements and gene bodies, and lowest in CpG islands (clusters of CpG sites, often near gene promoters).
DNA methylation analysis for episignature testing is typically performed on DNA from peripheral blood, using methylation arrays, though whole-genome bisulfite sequencing can achieve single-nucleotide resolution.
Other findings from the review:
• The Cornelia de Lange syndrome diagnostic scoring system assigns 2 points for cardinal features (such as synophrys, short nose, thin upper lip, hand defects, or diaphragmatic hernia) and 1 point for suggestive features (such as developmental delay, growth retardation, microcephaly, or hirsutism). A score ≥11 with at least 3 cardinal features indicates classic Cornelia de Lange syndrome; 9–10 points suggests non-classic; 4–8 warrants molecular testing; and <4 is insufficient for further evaluation.
• Cornelia de Lange syndrome is considered the prime example of CPs and can include growth retardation, craniofacial abnormalities, intellectual disability, hirsutism, genitourinary and limb defects, gastroesophageal reflux, and heart defects.
• NGS methods have broadly revolutionized genetic diagnosis, enabling identification of many new genes and loci for Mendelian disorders.
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