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ORPHA:261318Malformation syndrome
Also called Dup(20p) · Duplication of 20p · Partial duplication of chromosome 20p · Partial duplication of the short arm of chromosome 20 · Partial trisomy of chromosome 20p · Partial trisomy of the short arm of chromosome 20
What it is
Trisomy 20p is a chromosomal disorder resulting from duplication of all or part of the short arm of chromosome 20. It is mostly characterized by normal growth, mild to moderate intellectual disability, speech delay, poor coordination and evocative facial features.
Key facts
- Prevalence
- <1 / 1 000 000 (Europe)
- Age of onset
- Infancy, Neonatal
- Inheritance
- Not applicable, Unknown
- Classified as
- Malformation syndrome
Prevalence figures describe populations, not individuals, and are often estimates from a single study. Where the figure is an incidence or a birth prevalence, it says so.
Signs and symptoms
Very common80–99%
17- Abnormal autonomic nervous system physiology
- Abnormal facial shape
- Abnormal form of the vertebral bodies
- Abnormality of chromosome segregation
- Abnormality of speech or vocalization
- Cognitive impairment
- Full cheeks
- Gait disturbance
- Hernia
- Highly arched eyebrow
- Hypotonia
- Incoordination
- Joint hypermobility
- Protruding ear
- Round face
- Short neck
- Thick eyebrow
Common30–79%
25- Abnormal foot morphology
- Abnormality of the dentition
- Abnormality of the hip bone
- Abnormal palate morphology
- Anteverted nares
- Brachycephaly
- Brachydactyly
- Coarse hair
- Epicanthus
- Finger syndactyly
- Hypertelorism
- Inguinal hernia
- Low anterior hairline
- Low posterior hairline
- Macrotia
- Micrognathia
- Plagiocephaly
- Posteriorly rotated ears
- Short nose
- Spina bifida
- Strabismus
- Talipes
- Thick hair
- Umbilical hernia
- Upslanted palpebral fissure
These ranges are how often a sign appears across everyone diagnosed, not a prediction for one person — most people have some of these and not others. Orphanet also records findings that are specifically absent in this disease; those are in the data but not listed here.
ICD-10 codes
ICD-10 has no distinct code for most rare diseases, so many are filed under the nearest available one. A shared code identifies the group, not this disease — the ORPHAcode above is what identifies it.
Related health topics
Reached through the ICD-10 categories this disease is filed under, so these describe the broader group rather than this disease specifically.
Cross-references
Orphadata Science: Free access data from Orphanet. © INSERM 1999. Data version 2026-06-23. Available under CC BY 4.0. This is a reference, not medical advice.
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