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Start free with EleplanSchaaf-Yang syndrome
ORPHA:398069Disease
Also called SYS
What it is
A rare imprinting disorder characterized by muscular hypotonia, joint contractures/arthrogryposis, developmental delay, usually mild to moderate intellectual disability, short stature, hypogonadism, autism spectrum disorder and, less often, hyperphagia and seizures.
Key facts
- Prevalence
- <1 / 1 000 000
- Age of onset
- Antenatal, Neonatal
- Inheritance
- Not applicable
- Classified as
- Disease
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%
11Common30–79%
40- Abdominal obesity
- Abnormality of the eye
- Abnormal temper tantrums
- Absence of pubertal development
- Atypical behavior
- Autistic behavior
- Brain imaging abnormality
- Chronic constipation
- Clitoral hypoplasia
- Cognitive impairment
- Decreased fetal movement
- Decreased testicular size
- Delayed speech and language development
- External genital hypoplasia
- Failure to thrive
- Gastroesophageal reflux
- Hypogonadism
- Hypoplastic labia minora
- Hypothalamic luteinizing hormone-releasing hormone deficiency
- Increased body weight
- Intellectual disability, borderline
- Intellectual disability, mild
- Kyphosis
- Nasogastric tube feeding
- Polyphagia
- Primary amenorrhea
- Reduced tendon reflexes
- Scoliosis
- Short foot
- Short stature
- Skin-picking
- Sleep apnea
- Small hand
- Small pituitary gland
- Small scrotum
- Specific learning disability
- Strabismus
- Temperature instability
- Ventriculomegaly
- Weak cry
Sometimes5–29%
30- Abnormal rapid eye movement sleep
- Almond-shaped palpebral fissure
- Atrial septal defect
- Central hypothyroidism
- Central sleep apnea
- Chorioretinal hypopigmentation
- Compulsive behaviors
- Confusional arousal
and 22 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.
Gene
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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