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Pallister-Killian Syndrome (PKS)

Last updated Dec. 15, 2018

Approved by: Maulik P. Purohit MD MPH

Pallister-Killian Syndrome (PKS) is an infrequent, genetic developmental disorder that affects multiple parts of the body.


What are the other Names for this Condition? (Also known as/Synonyms)

  • Hexasomy 12p, Mosaic
  • Killian Syndrome
  • Pallister Mosaic Syndrome Tetrasomy 12p

What is Pallister-Killian Syndrome? (Definition/Background Information)

  • Pallister-Killian Syndrome (PKS) is an infrequent, genetic developmental disorder that affects multiple parts of the body
  • PKS is not an inherited condition; however, the genetic defect causing the disorder occurs in the womb, during or after the fertilization process. The signs and symptoms are observed during early infancy and childhood
  • A condition called hypotonia marks this disorder. It features extremely weak muscles with reduced strength and vitality, which can cause serious feeding and breathing problems in many infants
  • Other presentations include reduced hair density on the head, mental retardation, coarse facial appearance, and unusual pigmentation of the skin
  • Treatment of the condition is based on the severity and type of symptoms presented. Prognosis is dependent on many factors, including the presentations, access to early treatment, and is generally guarded

Who gets Pallister-Killian Syndrome? (Age and Sex Distribution)

  • Pallister-Killian Syndrome is an extremely rare condition that manifests itself at birth
  • No particular gender or racial/ethnic preference has been noted
  • Also, a detection of the condition in someone with mild symptoms, is difficult

What are the Risk Factors for Pallister-Killian Syndrome? (Predisposing Factors)

  • There are no established risk factors for Pallister-Killian Syndrome, since the disorder expresses itself spontaneously and randomly
  • Externally influencing factors such as food, environment or lifestyle, have not been currently supported by medical research as possible reasons of PKS occurrence

Studies are currently underway to determine the risk factors for Pallister-Killian Syndrome.

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Pallister-Killian Syndrome? (Etiology)

  • Pallister-Killian Mosaic Syndrome takes place due to a chromosomal anomaly, when two additional and defective copies of chromosome 12 (known as isochromosome 12p), are carried forward during fertilization. If all the cells have an extra copy of the chromosome, then medically it may not be life-sustaining
  • However, all body cells may not have this extra chromosome. Only a certain proportion of cells are found to have them. This causes a mixed cell population with different chromosome numbers (quantity-wise), a condition described as ‘mosaicism’
  • The severity of PKS, classified as mild or severe, is based directly on the proportion of the affected cells. If a large number of cells are affected, then it can cause greater signs and symptoms, as compared to a lesser number of cells being affected
  • It is researched that the anomaly lies, either in the egg cell or the sperm cell (maybe a cell division error), which after fertilization leads to the creation of extra copies of chromosome 12 (instead of two copies). This occurrence is irregular and happens sporadically
  • The exact mechanism of how the defective gene causes adverse multiple developmental conditions is yet to be fully understood

What are the Signs and Symptoms of Pallister-Killian Syndrome?

The signs and symptoms of Pallister-Killian Syndrome include:

  • Issues related to the nervous system:
    • Extreme hypotonia at birth
    • Epileptic seizures
    • Mental developmental delays
    • Hearing loss, lack of speech development
  • Issues related to the face and skull:
    • Sparse scalp hair, eyebrows and eyelashes
    • Coarse facial features
    • Large forehead
    • Pronounced appearance of ears and cheeks
    • Visual defects, such as strabismus, increased distance between the two eyes, skin folds at the upper eyelids, separation between the two eyelids
    • Flat, short nose
    • Oral defects, such as high palate, extended lower lip, thin upper lip, delayed teething
  • Other features include:
    • Large body size at birth
    • Non-uniform skin pigmentation
    • Gastroesophageal reflux disease (GERD), which can occur in early infancy
    • Congenital heart defects
    • Cataract of the eye
    • Soft larynx tissues causing breathing problems
    • Extra fingers and toes, fused skin between fingers or toes may be seen. Additional fingers and toes are called polydactyly; fusing of the skin between the fingers and toes is called syndactyly

How is Pallister-Killian Syndrome Diagnosed?

Diagnostic steps include a primary physical examination of the individual and gathering information related to the family medical history. The characteristic body features and clinical findings may help a physician understand the condition.

Some of the diagnostic tests performed for Pallister-Killian Syndrome include:

  • Skin biopsy
  • Buccal smear - a sample of cells from the mouth are studied
  • A panel of blood tests, which may include CBC
  • Molecular genetic analysis, chromosomal analysis
  • Prenatal diagnosis (during pregnancy) through amniocentesis, or chorionic villus sampling
  • Intra-uterine ultrasound of fetus, to screen for body features indicative of PKS
  • Imaging studies of the brain and spinal cord
  • Investigation of the heart condition, such as through echocardiogram and electrocardiogram

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Pallister-Killian Syndrome?

Complications due to Pallister-Killian Syndrome are generally uncommon. But, if PKS is severe, then the condition could be serious and the complications might include:

  • Breathing stoppage (temporary) or breathing trouble after birth, requiring immediate medical assistance
  • Diaphragmatic hernia - this condition is occasionally fatal
  • Vision loss, hearing impairment
  • Underdeveloped or improperly developed genitals
  • Gastrointestinal defects, abnormal kidney function
  • Reduced growth of head size and body length
  • Severe mental retardation
  • Severe heart defects
  • Hip dislocation at birth, abnormally curved spine (in two planes)
  • Social isolation and psychological issues, as the child develops

How is Pallister-Killian Syndrome Treated?

Treatment and management of Pallister-Killian Mosaic Syndrome is based on the severity of the condition and signs and symptoms presented. The treatment measures include:

  • Use of breathing aids (immediately after birth), in case of severe respiratory condition
  • Diaphragmatic hernia may require prompt and early surgical intervention
  • Use of hearing and vision aids to help with poor hearing and sight
  • Surgical procedures and braces are used to treat and rectify curvature of the spine
  • Surgical treatment of heart defects
  • Correctional surgery is performed to rectify hand and feet abnormalities (such as additional fingers or toes, fused skin between the fingers and toes)
  • Epileptic seizures are managed symptomatically with suitable medications
  • If there are developmental delays, then suitable supportive care and therapies are administered
  • Young children should undergo regular (annual) medical examination/screening, in order for the healthcare provider to assess their growth, and to also monitor for any abnormal developmental conditions

How can Pallister-Killian Syndrome be Prevented?

  • Medical researchers are still trying to understand the unique Pallister-Killian Syndrome and find ways to prevent its occurrence
  • Even though PKS is not an inherited syndrome, those with a family history of tetrasomy (disorder with extra pairs of chromosomes), should consider genetic counseling with DNA testing (even prenatal), before planning for another child

What is the Prognosis of Pallister-Killian Syndrome? (Outcomes/Resolutions)

  • Pallister-Killian Syndrome is a very rare disorder with multiple developmental abnormalities. It may be fatal, if the complications are severe
  • The disorder manifests in the womb, before birth of the child. Hence, it is difficult to predict the outcome of the condition. Growth from childhood to teenage, and into adulthood, gradually reveals the extent of the individual’s specific condition and severity of their signs and symptoms
  • Most babies require at birth, intensive care for a certain period of time due to inherent breathing difficulties. Once they begin to grow and develop, walking aids and supportive footwear are required. It is generally observed that the child’s mobility is affected, in most cases
  • The prognosis depends on the severity of the signs and symptoms. Individuals with milder PHS have much better prognosis, than individuals with severe conditions
  • Both mild and severe forms of the condition are treated symptomatically. Most individuals suffer from severe speech, hearing, and learning disabilities
  • Normally, lifelong medications with supportive care and therapy is required

Additional and Relevant Useful Information for Pallister-Killian Syndrome:

There are voluntary organizations and support groups that provide help and understanding to individuals and parents of Pallister-Killian Syndrome affected.

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Helpful Peer-Reviewed Medical Articles:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Dec. 30, 2013
Last updated: Dec. 15, 2018