About SYS

Schaaf-Yang Syndrome

What is Schaaf-Yang syndrome?

Schaaf-Yang syndrome (SYS) is a rare genetic disorder that affects various aspects of development, including intellectual ability, physical growth, and behavior. It is caused by a mutation or deletion of the MAGEL2 gene on chromosome 15q11-13, which is involved in the regulation of gene expression and brain development.

The disrupted gene causing Schaaf-Yang syndrome is also missing in another, more common genetic disorder, Prader-Willi syndrome (PWS). PWS is caused when MAGEL2 and several additional genes on chromosome 15 are missing or inactivated.

What are the symptoms of Schaaf-Yang syndrome?

The symptoms of Schaaf-Yang syndrome can vary widely between individuals but may include developmental delay, intellectual disability, speech and language difficulties, low muscle tone (hypotonia), feeding difficulties, behavioral problems, sleep disturbances, and distinctive facial features. Some individuals with SYS may also have skeletal abnormalities, seizures, and other health issues.

How is Schaaf-Yang syndrome diagnosed?

Schaaf-Yang syndrome can be passed down from the father to his offspring. However, in many cases, SYS is caused by a spontaneous genetic mutation that occurs during early development and is not inherited from either parent.

A suspected diagnosis of Schaaf-Yang Syndrome may be confirmed through whole exome sequencing or through MAGEL2 sequencing.

Have you recently received a diagnosis of Schaaf-Yang syndrome? Download First Steps: A Parent's Guide to SYS. This guide was written for parents, by parents and contains important information to help guide you through the beginning of this journey!

Frequently Asked Questions

Is there a cure for Schaaf-Yang syndrome?

Currently, there is no cure for Schaaf-Yang syndrome and treatment is based on managing the symptoms and providing supportive care. This may include physical therapy, speech therapy, behavioral interventions, and medication for specific symptoms. Genetic counseling may also be recommended for affected individuals and their families to discuss the risk of passing the condition on to future generations.

The Foundation for Prader-Willi Research is interested in advancing research toward understanding and treating specific aspects of the syndrome, with the goal of an eventual cure.

What are the similarities and differences between PWS and SYS?

Prader-Willi Syndrome (PWS) and Schaaf-Yang Syndrome (SYS) are both rare genetic disorders that affect various aspects of development, including intellectual ability, physical growth, and behavior. However, there are some differences between the two conditions, as well as some similarities.


  • Both PWS and SYS are caused by mutations or deletions in the same region of chromosome 15q11-13.
  • Both conditions can cause developmental delay, intellectual disability, speech and language difficulties, and behavioral problems.
  • Both PWS and SYS may be associated with low muscle tone (hypotonia), feeding difficulties, and sleep disturbances.
  • Both conditions can have an impact on physical growth and may cause short stature.


  • The genetic mutations that cause PWS and SYS are different. PWS is caused by the loss of function of paternal genes in the 15q11-13 region, whereas SYS is caused by mutations in the MAGEL2 gene in the same region.
  • Nearly all individuals with SYS have joint contractures.
  • Autism spectrum disorder is more common in individuals with SYS than PWS.
  • PWS is commonly associated with hyperphagia (an insatiable appetite) and obesity, while this is not a hallmark feature of SYS.

Dr. Christian Schaaf and his group, in collaboration with Dr. Jennifer Miller, have published the results of an FPWR-funded study examining the clinical similarities and differences between Prader-Willi syndrome (PWS) and Schaaf-Yang syndrome (SYS). Highlights from the paper are discussed in our blog: Study Compares Schaaf-Yang and Prader-Willi Syndromes.

What can I expect for an adult with Schaaf-Yang syndrome?

The adult phenotype for a person with Schaaf-Yang syndrome (SYS) is not well-defined due to the rarity of the condition and the limited number of cases that have been reported. However, based on available data, it appears that individuals with SYS may continue to experience a range of physical, developmental, and behavioral challenges into adulthood.

Developmental and intellectual disabilities associated with SYS persist into adulthood, and individuals with SYS may continue to experience difficulties with speech and language, learning, and social interactions. Behavioral issues such as anxiety, obsessive-compulsive tendencies, and autism spectrum disorders may also be present in some individuals with SYS, and these challenges may continue into adulthood.

In general, the adult phenotype for a person with SYS is likely to be highly variable and depend on a range of individual factors, including the severity of the genetic mutation, the presence of co-occurring health conditions, and the quality of support and interventions that the individual receives.

You can read more in the publication: The Adult Phenotype of Schaaf-Yang Syndrome (published in 2020).

Where can I learn more about Schaaf-Yang syndrome?

Recorded presentations from our SYS Family Conferences are available on our YouTube channel.

Watch presentations from Dr. Christian Schaaf, Dr. Ryan Potts, Dr. Rachel Wevrick, and others.  Learn more about the SYS research landscape, next steps in SYS research, and the clinical aspects of SYS in these conference presentations.

How can I get involved?

Our foundation relies on volunteers, like you, to help us accelerate our programs. We welcome you to join our team and get involved as we work together to eliminate the challenges of Schaaf-Yang and Prader-Willi syndromes.

SYS Fact Sheet

Download the Facts

This one-page fact sheet will give you a quick overview of:

  • Common SYS symptoms, including hypotonia and autism spectrum disorder
  • Differences and similarities between SYS and PWS
  • Research into treatments that offer hope for the future
  • How you can help!

To get the fact sheet, just fill out the form.


Get Involved

Anyone can fundraise for SYS research - parents, grandparents, brothers and sisters, aunts and uncles, or family friends. It can be as simple as setting up a fundraising page and sharing with your network through email and social media. Or it can be an in-person event such as a gala, a happy hour, a picnic, or cocktails in your home. The options are limitless and we are here to help you every step of the way. We can help you with graphic design, save the dates/invitations, e-blasts, an event webpage, and more. Set up your fundraising page today or contact info@fpwr.org to get started!

You can help find treatments for SYS.

Donate today!