National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Schaaf-Yang syndrome



Other Names:
Prader-Willi syndrome due to a point mutation; PWS due to a point mutation; MAGEL2-related Prader-Willi-like syndrome; Prader-Willi syndrome due to a point mutation; PWS due to a point mutation; MAGEL2-related Prader-Willi-like syndrome; MAGEL2-related PWLS; Prader-Willi syndrome due to point mutation; PWS due to point mutation; Prader-Willi-like syndrome See More
Categories:

Schaaf-Yang syndrome is a genetic condition that affects many parts of the body and is similar to Prader-Willi syndrome. Infants with this syndrome can have low muscle tone (hypotonia), feeding difficulties, developmental delay, intellectual disability, and autism spectrum disorder. They also typically have joint contractures, affecting the finger joints and sometimes the knees and elbows. This syndrome does not usually cause the high appetite seen in people with Prader-Willi syndrome. Schaaf-Yang syndrome is caused by a mutation in the MAGEL2 gene on chromosome 15. This syndrome is related to Prader-Willi syndrome because if MAGEL2 and several additional genes on chromosome 15 are missing or inactivated, then a person will develop Prader-Willi syndrome.[1][2] 
Last updated: 7/25/2017

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

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Medical Terms Other Names
Learn More:
HPO ID
5%-29% of people have these symptoms
Seizure 0001250
1%-4% of people have these symptoms
Arthrogryposis multiplex congenita 0002804
Fetal akinesia sequence 0001989
Percent of people who have these symptoms is not available through HPO
Abnormality of the philtrum 0000288
Absent speech
Absent speech development
Lack of language development
Lack of speech
No speech development
No speech or language development
Nonverbal
[ more ]
0001344
Autosomal dominant inheritance 0000006
Brachydactyly
Short fingers or toes
0001156
Camptodactyly
Permanent flexion of the finger or toe
0012385
Clinodactyly
Permanent curving of the finger
0030084
Coarse facial features
Coarse facial appearance
0000280
Constipation 0002019
Cryptorchidism
Undescended testes
Undescended testis
[ more ]
0000028
Delayed ability to walk 0031936
Esotropia
Inward turning cross eyed
0000565
Failure to thrive in infancy
Faltering weight in infancy
Weight faltering in infancy
[ more ]
0001531
Feeding difficulties
Feeding problems
Poor feeding
[ more ]
0011968
Flexion contracture
Flexed joint that cannot be straightened
0001371
Frontal bossing 0002007
Gastroesophageal reflux
Acid reflux
Acid reflux disease
Heartburn
[ more ]
0002020
Global developmental delay 0001263
Hypogonadism
Decreased activity of gonads
0000135
Impulsivity
Impulsive
0100710
Inability to walk 0002540
Infantile onset
Onset in first year of life
Onset in infancy
[ more ]
0003593
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific
Mental-retardation
[ more ]
0001249
Kyphosis
Hunched back
Round back
[ more ]
0002808
Low-set ears
Low set ears
Lowset ears
[ more ]
0000369
Mandibular prognathia
Big lower jaw
Increased projection of lower jaw
Increased size of lower jaw
Large lower jaw
Prominent chin
Prominent lower jaw
[ more ]
0000303
Micropenis
Short penis
Small penis
[ more ]
0000054
Myopia
Close sighted
Near sighted
Near sightedness
Nearsightedness
[ more ]
0000545
Narrow forehead
Decreased width of the forehead
0000341
Narrow palm 0004283
Neonatal hypotonia
Low muscle tone, in neonatal onset
0001319
Obesity
Having too much body fat
0001513
Open mouth
Gaped jawed appearance
Gaped mouthed appearance
Slack jawed appearance
[ more ]
0000194
Polyphagia
Voracious appetite
0002591
Retrognathia
Receding chin
Receding lower jaw
Weak chin
Weak jaw
[ more ]
0000278
Rocker bottom foot
Rocker bottom feet
Rocker-bottom feet
Rockerbottom feet
[ more ]
0001838
Scoliosis 0002650
Short foot
Short feet
Small feet
[ more ]
0001773
Short palpebral fissure
Short opening between the eyelids
0012745
Short stature
Decreased body height
Small stature
[ more ]
0004322
Sleep apnea
Pauses in breathing while sleeping
0010535
Small hand
Disproportionately small hands
0200055
Tapered finger
Tapered fingertips
Tapering fingers
[ more ]
0001182
Thick eyebrow
Bushy eyebrows
Dense eyebrow
Heavy eyebrows
Prominent eyebrows
Thick eyebrows
[ more ]
0000574
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Last updated: 7/1/2020

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources


Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease


These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

In-Depth Information

  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know.


  1. Schaaf-Yang syndrome. Foundation for Prader-Willi Research. https://www.fpwr.org/schaaf-yang-syndrome/. Accessed 7/25/2017.
  2. Fountain MD, Aten E, Cho MT, et al. The phenotypic spectrum of Schaaf-Yang syndrome – 18 new affected individuals from 14 families. Genetics in medicine?: official journal of the American College of Medical Genetics. 2017; 19(1):45-52. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5116288/.