Short answer · Medically reviewed summary · Last updated: 2026-05-08
Pallister-Killian syndrome, also known as tetrasomy 12p, is a rare genetic condition caused by the presence of an extra, abnormal chromosome (an isochromosome 12p) in some of the body's cells. This condition typically results in developmental delays, intellectual disability, distinctive facial features, and hypotonia (low muscle tone) that become apparent in early childhood. What causes Pallister-Killian syndrome? Pallister-Killian syndrome occurs due to a chromosomal error where an individual possesses an extra copy of the short arm of chromosome 12 in some cells.
What is Pallister-Killian Syndrome / Tetrasomy 12p
What is Pallister-Killian Syndrome / Tetrasomy 12p? Plain-language, medically reviewed definition plus the lived reality told by patients.
Pallister-Killian syndrome, also known as tetrasomy 12p, is a rare genetic condition caused by the presence of an extra, abnormal chromosome (an isochromosome 12p) in some of the body's cells. This condition typically results in developmental delays, intellectual disability, distinctive facial features, and hypotonia (low muscle tone) that become apparent in early childhood.
What causes Pallister-Killian syndrome?
Pallister-Killian syndrome occurs due to a chromosomal error where an individual possesses an extra copy of the short arm of chromosome 12 in some cells. Because this error usually happens after conception, it results in mosaicism, meaning only some cells in the body contain this extra genetic material. This mechanism is why the severity of Pallister-Killian syndrome symptoms can vary significantly from person to person.
How does Pallister-Killian syndrome affect the body?
The clinical presentation of Pallister-Killian syndrome is multisystemic. Common features often include:
- Hypotonia (low muscle tone) and developmental delay.
- Distinctive facial features, such as a high forehead, sparse scalp hair, and a wide gap between the eyes.
- Pigmentation changes, including patches of lighter or darker skin.
- Structural issues such as diaphragmatic hernia or heart defects.
- Seizures or hearing and vision impairments.
How common is Pallister-Killian syndrome?
Pallister-Killian syndrome is considered extremely rare, though its exact prevalence remains unknown because it is likely underdiagnosed. It affects both males and females equally, with no known geographical or ethnic predilection. While many cases are sporadic, our community at DiseaseMaps.org currently supports 9 individuals and families navigating the complexities of Pallister-Killian syndrome.
What differentiates this from other conditions?
Unlike many hereditary syndromes, Pallister-Killian syndrome is almost never inherited from parents. The presence of the extra isochromosome 12p is a "de novo" event. A key diagnostic challenge is that the abnormal cells may disappear from blood samples as a person ages, often requiring skin biopsies to confirm the diagnosis of Pallister-Killian syndrome.
Next steps
- Consult with a clinical geneticist to confirm a diagnosis via chromosomal microarray or skin fibroblast analysis.
- Schedule evaluations with specialists in neurology, cardiology, and ophthalmology.
- Connect with the DiseaseMaps.org community to share experiences with others affected by this condition.
- Seek early intervention programs for physical, occupational, and speech therapy.
Medical disclaimer: This information is for educational purposes only and should not replace professional medical advice, diagnosis, or treatment.
References
- NIH Genetic and Rare Diseases Information Center (GARD): Pallister-Killian syndrome
- Orphanet: Tetrasomy 12p mosaicism
- OMIM (Online Mendelian Inheritance in Man): Pallister-Killian Syndrome
- Pallister-Killian Syndrome Foundation
