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Coffin-Siris syndrome


ICD-10: Q87.1

ORPHA: 1465

General information

Estimated occurrence
Prevalence is currently unknown. There are approximately 200 individuals worldwide who have been diagnosed with this condition, of whom around 20 are in Sweden. The condition is probably underdiagnosed as symptoms could be minor.

To date, eight different gene mutations that give rise to CSS have been found. The genes are ARID1A, ARID1B, ARID2, DPF2, SMARCA4, SMARCB1, SMARCE1 and SOX11. A change in the ARID1B gene is the most common cause of the syndrome. All genes, except SOX11, code for proteins in what is known as the BAF complex, which affect the structure of the chromosomes. Although CSS is hereditary (autosomal dominant), in most cases it occurs as a new mutation.

General symptoms

CSS is characterised by a varying degree of intellectual and motor impairment. Autism and hyperactivity occur in some individuals. Motor development is often delayed and can also be affected by decreased muscle tone (hypotonia), which is often is seen early on in life. Joint hypermobility is common. Myelination – the process by which the layers of myelin that wrap around nerve fibres in the brain, the spine, and the rest of the nervous system are produced – could be slower, affecting both cognitive and motor development. The cerebral cortex, which connects the two halves of the brain (corpus callosum), could be underdeveloped or missing. Epilepsy occurs in around one-third of those with the condition. Short-sightedness and squinting are common, as is mild hearing loss. There could be low levels of thyroid hormone, and there is a slightly greater risk of diabetes. A number of individuals are born with minor heart defects, most commonly ASD, which is an abnormal opening in the septum (dividing wall) between the atria. Many of those with CSS have a slower rate of growth and are significantly shorter in stature. They sometimes share certain physical characteristics, such as an underdeveloped or missing nail on the little finger or little toe, prominent lips, thick eyebrows, long eyelashes, and a low hairline. There could be excessive hair growth on the body.


CSS, Fifth digit syndrome. Coffin-Siris syndrome is a collective name for several gene mutations. If the gene mutation has been identified, the condition sometimes takes the name of the gene, for example ARID1B syndrome.

Orofacial/odontological symptoms

A number of children are born with a cleft lip and palate. Eating difficulties are frequently noted. Low muscle tone and a soft larynx (laryngomalacia) could affect breathing and the ability to suck and swallow when the child is young. In most cases eating and breathing problems diminish with age, although it is not unusual for chewing difficulties, reduced appetite, selective eating, and affected sensitivity in the mouth to persist. Communication impairment is also common. Although the ability to express oneself is often affected, and some individuals do not have any spoken language, there is considerable variation within the group. Oral habits like biting and sucking on fingers or objects occur, and reduced saliva control is also seen in some individuals. Open mouth posture and facial hypotonia (decreased facial muscle tone) are typical. The midface area could be smaller than normal, which may result in congestion in the nose and throat, particularly if there is an infection. Tooth development in some individuals could be affected, including peg-shaped teeth, absence of a tooth buds, and mineralisation disturbances. Malocclusion is slightly more common in individuals with CSS.


National Board of Health and Welfare
Updated: 2022-11-11 09:36