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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Medical Genetics

Understanding Your Child's PKS Diagnosis

At a Glance

Pallister-Killian Syndrome (PKS) is a rare, non-inherited developmental disorder caused by an extra piece of chromosome 12 in some body cells. Because it does not always appear in blood cells, specialized skin or cheek swab tests are often needed for an accurate diagnosis.

Receiving a diagnosis of Pallister-Killian Syndrome (PKS) can feel overwhelming, especially since many healthcare providers may have limited experience with this rare condition [1][2]. This page is designed to help you move past the initial shock and understand the fundamental nature of PKS.

What is Pallister-Killian Syndrome?

Pallister-Killian Syndrome (PKS) is a rare multisystem developmental disorder caused by a specific genetic change [3]. Most people have two copies of every chromosome, but children with PKS have an extra, small “mirror-image” chromosome made of two copies of the short arm of chromosome 12 [1][4]. This is called isochromosome 12p [3].

The syndrome is mosaic, meaning the extra genetic material is not in every cell of the body [4][5]. It might be present in a high percentage of skin cells but a very low percentage—or not at all—in the blood [5][6]. This “hiding” nature is why PKS is often difficult to diagnose and why blood tests alone can sometimes miss it [5][7].

Three Stabilizing Facts for Families

When a diagnosis is new, it is helpful to focus on these core certainties:

  1. It is not your fault: PKS is almost always sporadic (occurring by chance) [3][8]. It is a de novo event, meaning it happens for the first time in the child and was not inherited from either parent [3][1]. There is nothing you did or didn’t do to cause this.
  2. Every child is unique: PKS is known for its variable expressivity [8][9]. This means that the symptoms and their severity can vary significantly from one child to another [1][10]. While PKS involves many systems of the body, your child’s journey will be their own.
  3. A diagnosis is a map, not a destination: Having a name for your child’s challenges allows for a multidisciplinary approach to care [11]. It ensures your medical team knows exactly what to screen for—such as hearing, vision, and heart health—to provide the best support early on [11][9].

Why the Diagnosis is Often Delayed

PKS is considered a rare condition, and while exact global incidence rates are difficult to define, it is frequently underdiagnosed [1][2]. The primary reasons for delays include:

  • Tissue-Specific Mosaicism: Because the extra chromosome may not be in the blood, standard karyotypes (chromosome maps) done on blood samples often come back normal [5][12]. Accurate diagnosis often requires testing alternative tissues like buccal swabs (cheek cells) or skin biopsies [13][14].
  • Subtle Early Signs: In some cases, the physical features of PKS may be subtle at birth, leading doctors to wait before ordering the specialized genetic testing required for detection [10][15].

What Research Knows vs. What is Uncertain

Science has a clear understanding of the “what” but is still working on the “how much.”

  • What is certain: PKS is caused by mosaic tetrasomy 12p [3][1]. We know it affects multiple systems, including the brain, facial structure, and skin pigmentation [11][15].
  • What is uncertain: There is currently no clear genotype-phenotype correlation in PKS [16][9]. This means that doctors cannot look at a genetic test and predict exactly how severe a child’s symptoms will be or exactly how they will develop over time [16]. The percentage of mosaic cells found in a sample does not always match the clinical severity seen in the child [16].

Because PKS is so rare, your local doctors may be learning alongside you. Connecting with a medical geneticist and specialized rare disease networks can help ensure your child receives the most current standards of care [17][11]. For more on the biology behind PKS, see PKS Biology and Diagnostic Testing.

Common questions in this guide

What causes Pallister-Killian Syndrome?
PKS is caused by a sporadic genetic change where a child has an extra, small mirror-image chromosome made of two copies of the short arm of chromosome 12. This is known as mosaic tetrasomy 12p. It occurs by chance and is not inherited from either parent.
Why did a normal blood test miss my child's PKS diagnosis?
PKS is a mosaic condition, meaning the extra genetic material is not present in every cell. It often hides and does not show up in blood cells, so standard chromosome tests on blood can come back normal. Doctors typically need to test cheek cells or a skin biopsy to confirm the diagnosis.
Will my child's genetic test predict how severe their PKS symptoms will be?
No, there is currently no clear correlation between genetic test results and symptom severity in PKS. The percentage of affected cells found in a test sample does not predict how your child will develop or the exact severity of their symptoms.
What specialists should be involved in my child's care for PKS?
Because PKS affects multiple systems in the body, care requires a multidisciplinary approach. Your child will likely need a medical geneticist, neurologist, cardiologist, and specialists in hearing and vision to provide comprehensive support and early screening.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What tissue was used for the diagnostic test, and is there a reason to test a second tissue type (like a skin biopsy or buccal swab)?
  2. 2.Can you explain the specific findings on my child's karyotype or microarray, and what 'mosaicism' means for their specific case?
  3. 3.How many other patients with PKS have you or this clinic managed, and who are the specialists (neurology, cardiology, etc.) we need on our team?
  4. 4.Which baseline screenings, such as a heart ultrasound (echocardiogram) or hearing test, should be scheduled immediately?
  5. 5.Are there any PKS-specific patient registries or natural history studies you recommend we join?

Questions For You

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References

References (17)
  1. 1

    A review of structural brain abnormalities in Pallister-Killian syndrome.

    Poulton C, Baynam G, Yates C, et al.

    Molecular genetics & genomic medicine 2018; (6(1)):92-98 doi:10.1002/mgg3.351.

    PMID: 29222831
  2. 2

    Prenatal diagnosis of a case with complete and uniform tetrasomy 12p by the utility of noninvasive prenatal testing.

    Zhang F, Yin T, Tang X, et al.

    Journal of assisted reproduction and genetics 2023; (40(9)):2233-2240 doi:10.1007/s10815-023-02896-8.

    PMID: 37501006
  3. 3

    Pineocytoma in a child with Pallister-Killian syndrome: a case report and review of the literature.

    De Martino L, Russo C, Bifano D, et al.

    Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery 2024; (40(8)):2619-2623 doi:10.1007/s00381-024-06426-4.

    PMID: 38689102
  4. 4

    Pallister-Killian syndrome: Review of fetal phenotype.

    Thakur S, Gupta R, Tiwari B, et al.

    Clinical genetics 2019; (95(1)):79-84 doi:10.1111/cge.13381.

    PMID: 29790157
  5. 5

    Postnatal clinical phenotype of five patients with Pallister-Killian Syndrome (tetrasomy 12p): Interest of array CGH for diagnosis and review of the literature.

    Alqahtani AS, Putoux A, Bonnet Dupeyron MN, et al.

    Molecular genetics & genomic medicine 2019; (7(10)):e00939 doi:10.1002/mgg3.939.

    PMID: 31454185
  6. 6

    Mosaic ratio quantification of isochromosome 12p in Pallister-Killian syndrome using droplet digital PCR.

    Fujiki K, Shirahige K, Kaur M, et al.

    Molecular genetics & genomic medicine 2016; (4(3)):257-61 doi:10.1002/mgg3.200.

    PMID: 27247953
  7. 7

    Using Array-Based Comparative Genomic Hybridization to Diagnose Pallister-Killian Syndrome.

    Lee MN, Lee J, Yu HJ, et al.

    Annals of laboratory medicine 2017; (37(1)):66-70 doi:10.3343/alm.2017.37.1.66.

    PMID: 27834069
  8. 8

    Prenatally identified Pallister-Killian syndrome: Ultrasound pattern and diagnostic considerations.

    Santamaria A, Laganà AS, Barresi V, et al.

    Journal of obstetrics and gynaecology : the journal of the Institute of Obstetrics and Gynaecology 2016; (36(3)):406-7 doi:10.3109/01443615.2015.1086984.

    PMID: 26471928
  9. 9

    Clinical Variability of Pallister-Killian Syndrome in Two Egyptian Patients.

    Eid MM, Eid OM, Abdel-Hadi S, et al.

    Journal of pediatric genetics 2020; (9(3)):207-210 doi:10.1055/s-0039-3400489.

    PMID: 32714624
  10. 10

    Pallister-Killian Mosaic Syndrome in an Omani Newborn: A Case Report and Literature Review.

    Elsheikh A, Al Shehhi M, Goud TM, et al.

    Oman medical journal 2019; (34(3)):249-253 doi:10.5001/omj.2019.47.

    PMID: 31110634
  11. 11

    Oro-dental features of Pallister-Killian syndrome: Evaluation of 21 European probands.

    Bagattoni S, D'Alessandro G, Sadotti A, et al.

    American journal of medical genetics. Part A 2016; (170(9)):2357-64 doi:10.1002/ajmg.a.37815.

    PMID: 27354242
  12. 12

    Fetoplacental cytogenetic discrepancy in a pregnancy with fetal mosaic tetrasomy 12p and Pallister-Killian syndrome detected by amniocentesis.

    Chen CP, Wang LK, Chern SR, et al.

    Taiwanese journal of obstetrics & gynecology 2017; (56(6)):852-856 doi:10.1016/j.tjog.2017.10.034.

    PMID: 29241934
  13. 13

    Prenatal diagnosis of Pallister-Killian syndrome and literature review.

    Wu X, Xie X, Su L, et al.

    Journal of cellular and molecular medicine 2021; (25(18)):8929-8935 doi:10.1111/jcmm.16853.

    PMID: 34405543
  14. 14

    Pallister-Killian Syndrome versus Trisomy 12p-A Clinical Study of 5 New Cases and a Literature Review.

    Arghir A, Popescu R, Resmerita I, et al.

    Genes 2021; (12(6)) doi:10.3390/genes12060811.

    PMID: 34073526
  15. 15

    Cognitive, Behavioral, and Sensory Profile of Pallister-Killian Syndrome: A Prospective Study of 22 Individuals.

    Fetta A, Soliani L, Trevisan A, et al.

    Genes 2022; (13(2)) doi:10.3390/genes13020356.

    PMID: 35205401
  16. 16

    Pallister-Killian Syndrome: The Diagnosis is in the Detail.

    Sailer S, Díaz GA, García MH, et al.

    Klinische Padiatrie 2019; (231(2)):93-95 doi:10.1055/a-0781-2564.

    PMID: 30517961
  17. 17

    Prenatal profile of Pallister-Killian syndrome: Retrospective analysis of 114 pregnancies, literature review and approach to prenatal diagnosis.

    Salzano E, Raible SE, Kaur M, et al.

    American journal of medical genetics. Part A 2018; (176(12)):2575-2586 doi:10.1002/ajmg.a.40499.

    PMID: 30289601

This page provides educational information about Pallister-Killian Syndrome for families and caregivers. It does not replace professional medical advice, diagnosis, or treatment planning from your child's medical geneticist or specialized healthcare team.

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