Au-Kline syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Au-Kline syndrome is a condition that affects many body systems. Individuals with this condition typically have weak muscle tone (hypotonia), intellectual disability, and delayed development. Speech is delayed in children with Au-Kline syndrome, and some are able to say only one or a few words or are never able to speak. In addition, affected children learn to walk later than usual, and some are never able to walk on their own.

Individuals with Au-Kline syndrome can have distinctive facial features, including long openings of the eyelids (long palpebral fissures), drooping eyelids (ptosis), and shallow eye sockets. Other common facial features in this condition include a broad nasal bridge, a mouth with the outer corners turned downward and often held in an open position, and a deep groove down the middle of the tongue. Less common abnormalities include premature joining of certain skull bones (craniosynostosis) in affected infants, an opening or unusually high arch in the roof of the mouth (cleft or high-arched palate), a split in the soft flap of tissue that hangs from the back of the mouth (bifid uvula), and missing teeth (oligodontia).

Malformations of the heart, blood vessels, kidneys, or bones can also occur in people with Au-Kline syndrome. For example, in some affected individuals, the large blood vessel that distributes blood from the heart to the rest of the body (the aorta) becomes weakened and stretched (aortic dilatation), which can be life-threatening. Some people with Au-Kline syndrome have an abnormal curvature of the spine (scoliosis). In addition, affected individuals may have difficulty feeding or poor vision.

Au-Kline syndrome can sometimes affect the autonomic nervous system, which controls involuntary body functions, such as digestion and regulation of body temperature. In people with Au-Kline syndrome, abnormalities in this system can lead to digestive problems, difficulty feeling pain, abnormal sweating, and an inability to adjust to high heat in people with Au-Kline syndrome.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Au-Kline syndrome is caused by mutations in the HNRNPK gene. The protein produced from this gene, called heterogenous nuclear ribonucleoprotein K (hnRNP K), attaches (binds) to DNA or its chemical cousin RNA and to other proteins, acting as a docking station for these molecules so they can interact. By bringing certain proteins together with DNA or RNA, the hnRNP K protein helps control the activity of genes and the production of proteins. By regulating certain genes and proteins, the hnRNP K protein plays a role in the normal development and function of several body systems, including the brain.

HNRNPK gene mutations that cause Au-Kline syndrome result in the production of little or no hnRNP K protein. A shortage of this protein alters gene activity and protein production, which disrupts the normal development or functioning of several body systems, resulting in the varied features of Au-Kline syndrome. In particular, problems with brain development likely contribute to intellectual disability, delayed development, and other neurological problems in people with the condition.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

Most cases of this condition result from new (de novo) mutations in the gene that occur during the formation of reproductive cells (eggs or sperm) in an affected individual’s parent or in early embryonic development. These cases occur in people with no history of the disorder in their family.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Au-Kline syndrome is a rare condition with an unknown prevalence. At least 25 cases have been diagnosed.

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 heart morphology · Very frequent (99-80%)

Any structural anomaly of the heart.

Abnormal helix morphology · Very frequent (99-80%)

An abnormality of the helix. The helix is the outer rim of the ear that extends from the insertion of the ear on the scalp (root) to the termination of the cartilage at the earlobe.

Abnormality of the genitourinary system · Very frequent (99-80%)

The presence of any abnormality of the genitourinary system.

Coarse facial features · Very frequent (99-80%)

Absence of fine and sharp appearance of brows, nose, lips, mouth, and chin, usually because of rounded and heavy features or thickened skin with or without thickening of subcutaneous and bony tissues.

Delayed speech and language development · Very frequent (99-80%)

A degree of language development that is significantly below the norm for a child of a specified age.

Hydronephrosis · Very frequent (99-80%)

Severe distention of the kidney with dilation of the renal pelvis and calices.

Hypotonia · Very frequent (99-80%)

Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.

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.

Other findings in the same source

From: Orphanet

Additional reported features include Long face (Very frequent (99-80%)); Long palpebral fissure (Very frequent (99-80%)); Motor delay (Very frequent (99-80%)); Wide nasal bridge (Very frequent (99-80%)); Poor speech (Very frequent (99-80%)); Abnormal autonomic nervous system physiology (Frequent (79-30%)); Cleft palate (Frequent (79-30%)); Constipation (Frequent (79-30%)); Craniosynostosis (Frequent (79-30%)); Cryptorchidism (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 Au-Kline 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 Au-Kline 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.