Pallister-Killian Syndrome in Babies
Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist
Content reviewed against published NIH, NORD, Unique guidelines
Last reviewed:
If your baby has been diagnosed with or you suspect pallister-killian syndrome in babies, here is what the evidence says.
The short answer
Pallister-Killian syndrome (PKS) is a rare chromosomal disorder caused by the presence of an extra isochromosome made up of two copies of the short arm of chromosome 12 (mosaic tetrasomy 12p). The extra chromosome is present in some cells but not all (mosaicism). Key features include characteristic facial features, significant hypotonia (low muscle tone), intellectual disability, streaks of skin with different coloring (pigmentary anomalies following lines of Blaschko), and seizures. Importantly, PKS is often NOT detectable on a standard blood karyotype and typically requires a skin biopsy (fibroblast karyotype) or buccal smear for diagnosis.
Key takeaways
- Pallister-Killian syndrome (PKS) is a rare chromosomal disorder caused by the presence of an extra isochromosome made up of two copies of the short arm of chromosome 12 (mosaic tetrasomy 12p). The extra chromosome is present in some cells but not all (mosaicism). Key features include characteristic facial features, significant hypotonia (low muscle tone), intellectual disability, streaks of skin with different coloring (pigmentary anomalies following lines of Blaschko), and seizures. Importantly, PKS is often NOT detectable on a standard blood karyotype and typically requires a skin biopsy (fibroblast karyotype) or buccal smear for diagnosis.
- Usually normal when: Your baby was evaluated for PKS and skin fibroblast testing (or other tissue-based testing) was negative
- Call your doctor if: Your baby has a seizure, clusters of infantile spasms, or prolonged seizure activity lasting more than 5 minutes
- Varies by age — see the age-by-age breakdown below
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What Parents Should Know
According to NIH, NORD, Unique guidelines, pallister-Killian syndrome (PKS) is a rare chromosomal disorder caused by the presence of an extra isochromosome made up of two copies of the short arm of chromosome 12 (mosaic tetrasomy 12p). The extra chromosome is present in some cells but not all (mosaicism). Key features include characteristic facial features, significant hypotonia (low muscle tone), intellectual disability, streaks of skin with different coloring (pigmentary anomalies following lines of Blaschko), and seizures. Importantly, PKS is often NOT detectable on a standard blood karyotype and typically requires a skin biopsy (fibroblast karyotype) or buccal smear for diagnosis. At 0-3 months, pKS may be suspected at birth based on the combination of distinctive facial features and significant hypotonia. Facial features include a high forehead, sparse hair in the temporal regions, a flat nasal bridge, widely spaced eyes, a short nose with anteverted nostrils, a long philtrum, a thin upper lip, and a full lower lip. Profound hypotonia is nearly universal and causes severe feeding difficulties, often requiring tube feeding. Diaphragmatic hernia occurs in about 5% of cases and may require surgical repair. A standard blood chromosome test may be normal - if PKS is suspected, a skin biopsy for fibroblast karyotype or fluorescence in situ hybridization (FISH) on buccal cells is needed. It is generally considered normal when your baby was evaluated for PKS and skin fibroblast testing (or other tissue-based testing) was negative. However, you should contact your pediatrician promptly if your baby has a seizure, clusters of infantile spasms, or prolonged seizure activity lasting more than 5 minutes.
Normal vs. Concerning
When to Seek Immediate Care
- Your baby has a seizure, clusters of infantile spasms, or prolonged seizure activity lasting more than 5 minutes
- Your baby is unable to feed adequately, is losing weight, or shows signs of aspiration (choking during feeds, recurrent pneumonia)
- Your newborn has signs of breathing difficulty that could indicate a diaphragmatic hernia (rapid breathing, bluish color, difficulty breathing)
- Your child with PKS becomes suddenly unresponsive, has severe breathing difficulties, or has signs of a serious infection
By Age
What to expect by age
0-3 months
PKS may be suspected at birth based on the combination of distinctive facial features and significant hypotonia. Facial features include a high forehead, sparse hair in the temporal regions, a flat nasal bridge, widely spaced eyes, a short nose with anteverted nostrils, a long philtrum, a thin upper lip, and a full lower lip. Profound hypotonia is nearly universal and causes severe feeding difficulties, often requiring tube feeding. Diaphragmatic hernia occurs in about 5% of cases and may require surgical repair. A standard blood chromosome test may be normal - if PKS is suspected, a skin biopsy for fibroblast karyotype or fluorescence in situ hybridization (FISH) on buccal cells is needed.
3-12 months
Feeding difficulties and hypotonia remain significant challenges. Seizures may begin in infancy, sometimes in the form of infantile spasms, which require prompt treatment. Pigmentary skin anomalies may become more apparent, appearing as streaks or patches of lighter or darker skin following the lines of Blaschko (curved lines on the body). These are most visible in sun-exposed areas or under Wood lamp examination. Hearing loss occurs in many children and should be evaluated. Cardiac defects are present in about 25% of cases.
1-3 years
Developmental delays are significant in all areas. Some children with milder mosaicism may sit independently and develop a few words, while more severely affected children may have minimal voluntary movement and no speech. Seizures may be difficult to control. The sparse temporal hair that was present at birth often fills in during early childhood. Joint contractures may develop due to limited movement. Streaky pigmentation patterns become more distinctive and can help support the clinical diagnosis.
3 years+
Children with PKS continue to require intensive support and medical management. Seizures may improve with age in some individuals. Scoliosis and musculoskeletal complications may develop due to hypotonia and limited mobility. Vision and hearing should be monitored regularly. Despite the significant challenges, many individuals with PKS show awareness of and engagement with their environment, respond to familiar people, and can participate in sensory activities. Life expectancy varies depending on severity, but many individuals live into adulthood.
What to Tell Your Pediatrician
- Describe when you first noticed pallister-killian syndrome in babies and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if your baby has significant hypotonia combined with distinctive facial features and you want to discuss testing for PKS.
- Mention if your baby has streaky skin pigmentation along with developmental delays and you want to discuss whether fibroblast karyotype testing is appropriate.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
What Should You Do?
When to take action
- Your baby was evaluated for PKS and skin fibroblast testing (or other tissue-based testing) was negative
- Your baby has areas of different skin pigmentation that are isolated and not associated with other PKS features (several other conditions can cause pigmentary mosaicism)
- A standard blood karyotype was normal - but note that this does NOT rule out PKS (tissue-based testing is needed if clinical suspicion is high)
- Your baby has significant hypotonia combined with distinctive facial features and you want to discuss testing for PKS
- Your baby has streaky skin pigmentation along with developmental delays and you want to discuss whether fibroblast karyotype testing is appropriate
- Your child with PKS is having increasing seizure frequency or new seizure types
- You want to discuss genetic counseling, the diagnosis, or long-term management plans
- Your baby has a seizure, clusters of infantile spasms, or prolonged seizure activity lasting more than 5 minutes
- Your baby is unable to feed adequately, is losing weight, or shows signs of aspiration (choking during feeds, recurrent pneumonia)
- Your newborn has signs of breathing difficulty that could indicate a diaphragmatic hernia (rapid breathing, bluish color, difficulty breathing)
- Your child with PKS becomes suddenly unresponsive, has severe breathing difficulties, or has signs of a serious infection
What You Can Do at Home
- Keep track of when you notice pallister-killian syndrome in babies — noting the time of day, duration, and any triggers can help your pediatrician.
- Remember that your baby was evaluated for PKS and skin fibroblast testing (or other tissue-based testing) was negative — this is generally within the range of normal.
- At 0-3 months, focus on observation rather than intervention unless your pediatrician advises otherwise.
- Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
- While monitoring at home, seek immediate care if your baby has a seizure, clusters of infantile spasms, or prolonged seizure activity lasting more than 5 minutes.
Related Conditions
Low Muscle Tone (Hypotonia)
Low muscle tone means your baby's muscles feel less firm or their body feels "floppy" when you hold them. While it can sometimes indicate an underlying condition, many babies with mildly low tone do very well with support and strengthening activities.
Types of Seizures in Babies and What They Look Like
Seizures in babies can look very different from seizures in adults. Types include subtle seizures (eye deviation, lip smacking, bicycling movements), tonic seizures (stiffening), clonic seizures (rhythmic jerking), myoclonic seizures (quick jerks), and infantile spasms (clusters of brief body flexion). Any suspected seizure in a baby needs medical evaluation. Video-recording the episode on your phone is extremely helpful for your doctor to determine if it was truly a seizure.
Uneven Skin Coloring in Baby
Uneven skin coloring in babies is very common and usually harmless. Newborn skin naturally has variations in pigment as melanin production matures. Conditions like cutis marmorata (mottling), post-inflammatory pigment changes, and birthmarks can all cause uneven coloring. Most variations even out over time.
Related Resources
Frequently asked questions
Is pallister-killian syndrome in babies normal?
When should I call the doctor about pallister-killian syndrome in babies?
When is pallister-killian syndrome in babies normal?
What causes pallister-killian syndrome in babies?
What should I mention to my pediatrician about pallister-killian syndrome in babies?
Is pallister-killian syndrome in babies normal at 0-3 months?
Is pallister-killian syndrome in babies normal at 3-12 months?
Should I go to the ER for pallister-killian syndrome in babies?
Does pallister-killian syndrome in babies go away on its own?
References
- [1]National Institutes of Health. Pallister-Killian Mosaic Syndrome. Genetic and Rare Diseases Information Center (GARD). NIH
- [2]National Organization for Rare Disorders. Pallister-Killian Mosaic Syndrome. NORD Rare Disease Database. NORD
- [3]Unique - Rare Chromosome Disorder Support Group. Pallister-Killian Syndrome: Information for Families. Unique
Doctor Visit Checklist
Bring this checklist to your next pediatrician visit to discuss Pallister-Killian Syndrome in Babies.
Things to mention
- Describe when you first noticed pallister-killian syndrome in babies and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if your baby has significant hypotonia combined with distinctive facial features and you want to discuss testing for PKS.
- Mention if your baby has streaky skin pigmentation along with developmental delays and you want to discuss whether fibroblast karyotype testing is appropriate.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
Observations to share
- Your baby has significant hypotonia combined with distinctive facial features and you want to discuss testing for PKS
- Your baby has streaky skin pigmentation along with developmental delays and you want to discuss whether fibroblast karyotype testing is appropriate
- Your child with PKS is having increasing seizure frequency or new seizure types
Urgent signs to report immediately
- Your baby has a seizure, clusters of infantile spasms, or prolonged seizure activity lasting more than 5 minutes
- Your baby is unable to feed adequately, is losing weight, or shows signs of aspiration (choking during feeds, recurrent pneumonia)
- Your newborn has signs of breathing difficulty that could indicate a diaphragmatic hernia (rapid breathing, bluish color, difficulty breathing)
My notes
From ismybabyalright.com — free, evidence-based baby health guides
All content follows our editorial policy and is reviewed against published clinical guidelines.
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Related Resources
Bottom line
Most cases of pallister-killian syndrome in babies are normal. Talk to your pediatrician if your baby has a seizure, clusters of infantile spasms, or prolonged seizure activity lasting more than 5 minutes.
Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.
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Related Medical Concerns
Low Muscle Tone (Hypotonia)
Low muscle tone means your baby's muscles feel less firm or their body feels "floppy" when you hold them. While it can sometimes indicate an underlying condition, many babies with mildly low tone do very well with support and strengthening activities.
Types of Seizures in Babies and What They Look Like
Seizures in babies can look very different from seizures in adults. Types include subtle seizures (eye deviation, lip smacking, bicycling movements), tonic seizures (stiffening), clonic seizures (rhythmic jerking), myoclonic seizures (quick jerks), and infantile spasms (clusters of brief body flexion). Any suspected seizure in a baby needs medical evaluation. Video-recording the episode on your phone is extremely helpful for your doctor to determine if it was truly a seizure.
Uneven Skin Coloring in Baby
Uneven skin coloring in babies is very common and usually harmless. Newborn skin naturally has variations in pigment as melanin production matures. Conditions like cutis marmorata (mottling), post-inflammatory pigment changes, and birthmarks can all cause uneven coloring. Most variations even out over time.
My Baby's Head Shape Looks Abnormal
Many babies develop temporary head shape irregularities that are completely normal. A cone-shaped head from vaginal delivery reshapes within days. Mild positional flattening (plagiocephaly) from sleeping on the back is very common and usually improves with repositioning and tummy time. However, head shape changes involving ridges, a persistently bulging fontanelle, or rapid head growth changes should be evaluated to rule out craniosynostosis.
Achondroplasia (Dwarfism) in Babies
Achondroplasia is the most common form of short-limbed dwarfism, affecting about 1 in 15,000 to 40,000 births. It is caused by a mutation in the FGFR3 gene and is usually apparent at birth with characteristic features including short limbs, a larger head, and a prominent forehead. Intelligence is normal. With monitoring for specific complications and supportive care, children with achondroplasia lead full, active, and independent lives.
Adenoid Hypertrophy and Breathing
Adenoids are lymphoid tissue located behind the nose that help fight infection in young children. When adenoids become enlarged (adenoid hypertrophy), they can block the nasal airway, causing chronic mouth breathing, snoring, nasal speech, and sleep-disordered breathing. Enlarged adenoids are most common between ages 2-7 and are a leading cause of obstructive sleep apnea in young children. Treatment ranges from watchful waiting and nasal steroids to surgical removal (adenoidectomy) if breathing or sleep is significantly affected.