KCNK9 imprinting syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

KCNK9 imprinting syndrome is a rare condition characterized by weak muscle tone (hypotonia) from birth. As a result, affected infants have a lack of energy (lethargy), a weak cry, and they move less than normal. Facial weakness and a poor ability to suck cause feeding difficulties, which can lead to an inability to grow and gain weight (faltering weight). Difficulty swallowing (dysphagia) often lasts into adolescence. While muscle tone may improve over time, affected individuals usually have some weakness into adulthood. The weakness can lead to permanently bent joints (contractures) and abnormal curvature of the spine (scoliosis).

KCNK9 imprinting syndrome is also characterized by intellectual disability and delayed development of speech and motor skills, such as sitting and walking. Many affected individuals have limited speech throughout life.

This condition is associated with unusual facial features, including an elongated face that narrows at the temples; an upper lip that points outward (called a tented lip); a short, broad space between the lip and the nose (philtrum); a small lower jaw (micrognathia); and abnormally shaped eyebrows. Some affected individuals have an opening in the roof of the mouth (cleft palate). In addition to unusual facial features, some people with KCNK9 imprinting syndrome have a long neck, a narrow chest, and tapered fingers.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the KCNK9 gene cause KCNK9 imprinting syndrome. This gene provides instructions for making a protein called TASK3, which functions as a potassium channel. Potassium channels transport positively charged atoms (ions) of potassium into and out of cells.

TASK3 channels are especially abundant in nerve cells (neurons) in the brain, particularly the region of the brain that coordinates movement (cerebellum). The flow of ions through potassium channels in neurons is involved in activating (exciting) the neurons and sending electrical signals in the brain. TASK3 channels, in particular, maintain the neuron's ability to generate electrical signals and regulate the neuron's activity (excitability).

The genetic changes that cause KCNK9 imprinting syndrome alter the TASK3 channels. This alteration reduces the flow of ions through the channels, which disrupts normal neuron development and excitability. Impairment of neuron function likely underlies the hypotonia, intellectual disability, and developmental problems characteristic of KCNK9 imprinting syndrome.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

KCNK9 imprinting syndrome follows an autosomal dominant pattern of inheritance, which means one copy of the altered gene in each cell is sufficient to cause the disorder. People inherit two copies of their genes, one from their mother and one from their father. Usually both copies of each gene are active, or "turned on," in cells. However, for some genes, including KCNK9, only one of the two copies is normally turned on, which is a phenomenon known as genomic imprinting. The KCNK9 gene is a maternally expressed imprinted gene, which means that only the copy of the gene that comes from the mother is active. The copy of the gene that comes from the father is turned off (silenced).

In most cases of KCNK9 imprinting syndrome, an affected person inherits the mutation from his or her mother. Because the copy of the gene from the father is silenced, fathers cannot pass the condition to their kids. About 20 percent of cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

KCNK9 imprinting syndrome is a rare condition. At least 19 affected individuals have been described in the medical literature.

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.

Broad nasal tip · Frequent (79-30%)

Increase in width of the nasal tip.

Broad philtrum · Frequent (79-30%)

Distance between the philtral ridges, measured just above the vermilion border, more than 2 standard deviations above the mean, or alternatively, an apparently increased distance between the ridges of the philtrum.

Dolichocephaly · Frequent (79-30%)

An abnormality of skull shape characterized by a increased anterior-posterior diameter, i.e., an increased antero-posterior dimension of the skull. Cephalic index less than 76%. Alternatively, an apparently increased antero-posterior length of the head compared to width. Often due to premature closure of the sagittal suture.

Dysphagia · Frequent (79-30%)

Difficulty in swallowing.

Dysphonia · Frequent (79-30%)

Difficulty in speaking due to a physical disorder of the mouth, tongue, throat, or vocal cords. Associated with a known physical or neurological cause.

Fatigable weakness of skeletal muscles · Frequent (79-30%)

A type of weakness of skeletal muscle that occurs after a muscle group is used and lessens if the muscle group has some rest. That is, there is diminution of strength with repetitive muscle actions.

Fatiguable weakness of proximal limb muscles · Frequent (79-30%)

A type of weakness of a skeletal muscle of proximal part of a limb that occurs after a muscle group is used and lessens if the muscle group has some rest. That is, there is diminution of strength with repetitive muscle actions.

Feeding difficulties · Frequent (79-30%)

Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it.

Other findings in the same source

From: Orphanet

Additional reported features include Generalized hypotonia (Frequent (79-30%)); Global developmental delay (Frequent (79-30%)); High, narrow palate (Frequent (79-30%)); Highly arched eyebrow (Frequent (79-30%)); Hyperactivity (Frequent (79-30%)); Hypomimic face (Frequent (79-30%)); Incisor macrodontia (Frequent (79-30%)); Micrognathia (Frequent (79-30%)); Narrow forehead (Frequent (79-30%)); Narrow nasal bridge (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing KCNK9 imprinting 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 KCNK9 imprinting 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.