Kabuki syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Kabuki syndrome is a disorder that can affect many parts of the body. It is characterized by distinctive facial features including arched eyebrows; long eyelashes; long openings of the eyelids (long palpebral fissures) with the lower lids turned out (everted) at the outside edges; a flat, broadened tip of the nose; and large protruding earlobes. The name of this disorder comes from the resemblance of its characteristic facial appearance to stage makeup used in traditional Japanese Kabuki theater.

People with Kabuki syndrome may have mild to severe developmental delay and intellectual disability. Affected individuals may also have seizures, an unusually small head size (microcephaly), or weak muscle tone (hypotonia). Some have eye problems such as rapid, involuntary eye movements (nystagmus) or eyes that do not look in the same direction (strabismus).

Other characteristic features of Kabuki syndrome include short stature and skeletal abnormalities such as abnormal side-to-side curvature of the spine (scoliosis), short fifth (pinky) fingers, or problems with the hip and knee joints. The roof of the mouth may have an abnormal opening (cleft palate) or be high and arched, and dental problems are common in affected individuals. People with Kabuki syndrome may also have fingerprints with unusual features and fleshy pads at the tips of the fingers. These prominent finger pads are called fetal finger pads because they normally occur in human fetuses; in most people they disappear before birth.

A wide variety of other health problems occur in some people with Kabuki syndrome. Among the most commonly reported are heart abnormalities, frequent ear infections (otitis media), hearing loss, and early puberty.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Kabuki syndrome is caused by variants (also known as mutations) in the KMT2D gene (also known as MLL2) or the KDM6A gene.

Between 55 and 80 percent of cases of Kabuki syndrome are caused by variants in the KMT2D gene. This gene provides instructions for making an enzyme, called lysine-specific methyltransferase 2D, that is found in many organs and tissues of the body. Lysine-specific methyltransferase 2D functions as a histone methyltransferase. Histone methyltransferases are enzymes that modify proteins called histones. Histones are structural proteins that attach (bind) to DNA and give chromosomes their shape. By adding a molecule called a methyl group to histones (a process called methylation), histone methyltransferases control (regulate) the activity of certain genes. Lysine-specific methyltransferase 2D appears to activate certain genes that are important for development.

Between 2 and 6 percent of cases of Kabuki syndrome are caused by variants in the KDM6A gene. This gene provides instructions for making an enzyme called lysine-specific demethylase 6A. This enzyme is a histone demethylase, which means that it helps to remove methyl groups from certain histones. Like lysine-specific methyltransferase 2D, lysine-specific demethylase 6A regulates the activity of certain genes, and research suggests that the two enzymes work together to control certain developmental processes.

The KMT2D and KDM6A gene variants associated with Kabuki syndrome lead to the absence of the corresponding functional enzyme. A lack of either of the enzymes produced from these genes disrupts normal histone methylation and impairs proper activation of certain genes in many of the body's organs and tissues, resulting in the abnormalities of development and function characteristic of Kabuki syndrome.

Some people with Kabuki syndrome have no identified KMT2D or KDM6A gene variant. These individuals are diagnosed based on the presence of characteristic features of the condition. The cause of Kabuki syndrome in these individuals is unknown.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

When Kabuki syndrome is caused by variants in the KMT2D gene, it is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

When Kabuki syndrome is caused by variants in the KDM6A gene, it is inherited in an X-linked dominant pattern. The KDM6A gene is located on the X chromosome, which is one of the two sex chromosomes. In females (who have two X chromosomes), a variant in one of the two copies of the gene in each cell is sufficient to cause the disorder. In males (who have only one X chromosome), a variant in the only copy of the gene in each cell causes the disorder. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

Most cases of Kabuki syndrome result from a new variant in one of these genes and occur in people with no history of the disorder in their family. In a few cases, an affected person is believed to have inherited the variant from one affected parent.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Kabuki syndrome occurs in approximately 1 in 32,000 newborns.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal dermatoglyphics · Very frequent (99-80%)

An abnormality of dermatoglyphs (fingerprints), which are present on fingers, palms, toes, and soles.

Abnormal form of the vertebral bodies · Very frequent (99-80%)

Abnormal form of vertebral body, which is the central cylindrical portion of the vertebra that together with other structures such as the vertebral arch, pedicles, laminae, spinous process, transverse processes, and articular facets makes up a vertebra.

Abnormality of the outer ear · Very frequent (99-80%)

An abnormality of the external ear.

Butterfly vertebrae · Very frequent (99-80%)

A butterfly vertebra (sagittal cleft vertebra or anterior rachischisis) is a sagittal defect in the vertebral body caused by failure of fusion of the two lateral chondrification centers during embryogenesis. The name is based on the appearance of the two hemivertebrae emerging as butterfly wings from the central cleft on x-ray.

Hemivertebrae · Very frequent (99-80%)

Absence of one half of the vertebral body.

Highly arched eyebrow · Very frequent (99-80%)

Increased height of the central portion of the eyebrow, forming a crescent, semicircular, or inverted U shape.

Intellectual disability · Very frequent (99-80%)

The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence.

Long eyelashes · Very frequent (99-80%)

Mid upper eyelash length >10 mm or increased length of the eyelashes (subjective).

Other findings in the same source

From: Orphanet

Additional reported features include Macrotia (Very frequent (99-80%)); Neurodevelopmental delay (Very frequent (99-80%)); Postnatal growth retardation (Very frequent (99-80%)); Protruding ear (Very frequent (99-80%)); Short 5th finger (Very frequent (99-80%)); Short columella (Very frequent (99-80%)); Short middle phalanx of finger (Very frequent (99-80%)); Sparse lateral eyebrow (Very frequent (99-80%)); Vertebral clefting (Very frequent (99-80%)); Eversion of lateral third of lower eyelids (Very frequent (99-80%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Kabuki syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Kabuki syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.