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Start free with EleplanMonosomy 18q syndrome
ORPHA:1600Malformation syndrome
Also called 18q deletion syndrome · 18q- syndrome · De Grouchy syndrome type 2 · Deletion 18q
What it is
A partial deletion of the long arm of chromosome 18 characterized by highly variable phenotype, most commonly including hypotonia, developmental delay, short stature, growth hormone deficiency, hearing loss and external ear anomalies, intellectual disability, palatal defects, dysmorphic facial features, skeletal anomalies (foot deformities, tapering fingers, scoliosis) and mood disorders.
Key facts
- Prevalence
- 1-9 / 100 000 (at birth)
- Age of onset
- Antenatal, Neonatal
- Inheritance
- Autosomal dominant
- 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
Common30–79%
29- Abnormal facial shape
- Abnormal myelination
- Abnormal palmar dermatoglyphics
- Abnormal retinal morphology
- Arachnodactyly
- Bilateral conductive hearing impairment
- Bilateral cryptorchidism
- Delayed skeletal maturation
- Depressed nasal bridge
- Diffuse white matter abnormalities
- Downturned corners of mouth
- Global developmental delay
- Growth delay
- Intellectual disability
- Intellectual disability, mild
- Kyphoscoliosis
- Macrotia
- Mandibular prognathia
- Micropenis
- Myopia
- Neonatal hypotonia
- Patent ductus arteriosus
- Pes planus
- Poor coordination
- Pulmonary valve defects
- Secondary growth hormone deficiency
- Short stature
- Talipes equinovarus
- Tapered finger
Sometimes5–29%
34- Absence of the pulmonary valve
- Aortic aneurysm
- Aortic valve stenosis
- Biparietal narrowing
- Bulbous nose
- Cerebellar hypoplasia
- Choanal stenosis
- Choreoathetosis
and 26 more in this range
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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