Prader Willi Syndrome

Updated April 24, 2019

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Prader Willi syndrome is a rare genetic disorder that only affects about 1 in 15,000 births 1. Children and adults with the disorder need to appropriately manage their symptoms in order to have a good quality of life.

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Disclaimer: Before You Read

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What is Prader Willi Syndrome?

Prader Willi Syndrome, also known as PWS, is a rare and complex genetic disorder that affects multiple body systems.

It can occur in males or females, of any race or ethnic background.

Common traits include small feet and hands, a small stature, weak muscles, intellectual disability, behavioral problems, delayed puberty and an uncontrollable appetite that can lead to childhood obesity.

Is Prader Willi Syndrome Hereditary?

For the most part, no. However, in extremely rare cases due to a change in the paternal chromosome 15 that inactivates the genes, Prader Willi Syndrome can be passed down from one generation to another.

In most cases, though, it's not hereditary and happens as a result of a deletion that occurs in part of chromosome 15 2.

What Causes Prader Willi Syndrome?

In about 70 percent of the confirmed cases of Prader Willi Syndrome, people are missing a segment of chromosome 15.

This occurrence causes a chromosomal change wherein critical genes have been deleted and the ones acquired from the maternal copy remain inactive.

In roughly 25 percent of the cases, the person receives two copies of the chromosome 15 from one parent instead of one from each of their parents.

In maternal uniparental disomy, both copies come from the mother, resulting in inactive genes.

In very few cases a chromosomal rearrangement, also known as a translocation, or a mutation occurs that makes the paternal chromosome 15 genes inactive.

Which Gene Is Imprinted in Prader Willi Syndrome?

Imprinted genes are rare genes that possess the ability to turn on/off, depending on their source, either obtained from the mother or the father.

With Prader Willi Syndrome the copy of chromosome 15 inherited from the mother remains turned off, or inactive.

In order for the gene to perform its normal function, the father's contributing chromosome 15 must remain uncompromised, intact and active.

Can Prader Willi Syndrome Be Prevented?

Prader Willi Syndrome occurs at the time of conception. Since the disorder occurs randomly, there currently is no way to prevent it.

Diagnosis of Prader Willi Syndrome

Prader Willi Syndrome has many symptoms that parents can watch out for if they suspect their child may have the genetic disorder.

During infancy, a child may have difficulty feeding such as sucking while breastfeeding or drinking from a bottle.

They may also have weak muscles, a soft cry and poor reflexes.

Additionally, baby boys may have undescended testicles and girls may have underdeveloped genitalia.

There are also other distinct features such as almond-shaped or crossed eyes, a thin upper lip with downturned mouth, a narrow forehead particularly at the temples and small hands and feet.

As children grow older, they tend to eat often and have an increased appetite otherwise known as hyperphagia.

How Do You Diagnose Prader Willi Syndrome?

If a child or an adult has characteristics and shows multiple signs or symptoms of Prader Willi Syndrome, their primary physician can test them to either confirm it or rule it out.

How Do Doctors Test for Prader Willi Syndrome?

There are several tests a doctor can order for patients to determine whether or not they have Prader Willi Syndrome.

Most often a physician will do a DNA Methylation analysis blood test as it can identify accurately all cases of PWS.

Generally, as a follow up to the methylation test, a doctor will also do a FISH blood test.

However, this test will only identify people that have Prader Willi Syndrome caused from a deletion of a section of the chromosome 15, and not those who have it resulting from uniparental disomy or imprinting mutilation.

Chromosome microarray (CMA) is a newer test gaining recognition and preference among physicians.

It can detect most chromosome deletions, including those of atypical size, although it can't detect cases involving imprinting defects.

What Age Is Prader Willi Syndrome Diagnosed?

There is no specific age for a diagnosis of Prader Willi Syndrome 3. However, meeting the diagnostic criteria is often the basis for prompting testing.

Infants who meet the major criteria may have trouble sucking while breastfeeding or drinking from a bottle, possess weak muscles, have slow growth development and exhibit facial characteristics such as a narrow forehead and a downturned mouth.

Toddlers and young children between the ages of 1 and 6 often show early signs of child obesity caused by an uncontrolled appetite, have underdeveloped genitalia and present with learning disabilities. Minor symptoms can include:

  • Short stature
  • Behavioral and sleep problems
  • Poor pronunciation
  • Habit of skin picking

Diagnosis of this genetic disorder in adults is based on meeting the same signs and symptoms and then followed up with testing to confirm.

Prader Willi Syndrome and Genetics

The genetic disorder happens randomly in roughly 1 out of every 15,000 births. It's also not predisposed to any race, gender or ethnic background.

The cause of this rare disorder comes from an abnormality with chromosome 15.

The only way to make a final determination with a definitive diagnosis is through genetic testing for Prader Willi Syndrome.

Genetic Tests for Prader Willi Syndrome - Are They Available?

Genetic tests are available for Prader Willi Syndrome 4. In fact, there are several that doctors use, with proven results.

Currently, doctors mainly do a DNA methylation analysis blood test as it can provide accurate results regarding all cases of PWS.

Chromosome microarray (CMA), while newer, is also preferred among physicians. However, it cannot detect cases caused by imprinting defects.

There are currently no at-home DNA tests available, all tests go through a doctor or independent laboratory with genomic sequencing.

What Laboratory Studies Should You Request to Help Confirm the Diagnosis?

While a person must meet the criteria, which includes exhibiting several specific symptoms, the diagnosis always requires a series of blood tests that doctors order.

Specialists then take the blood samples to study the methylation patterns located within a section of chromosome 15, 15q11 to q13, using specific genetic techniques.

This will allow the specialists to do Prader Willi syndrome research to determine not only if the patient has the syndrome but also the cause.

DNA Testing to Spot or Detect Prader Willi Syndrome Early

Generally, testing will not take place during pregnancy unless the mother is at high risk for having a child with PWS.

A doctor may order testing if the parent has another child that has the genetic disorder and the cause is due to either a parental chromosome translocation or imprinting defect.

These parents may be recommended for genetic counseling where the counselor will evaluate and explain the risks involved.

Testing for Prader Willi Syndrome on a Pregnancy or Before a Pregnancy Is Achieved

If a mother is at a higher risk for having a baby with PWS, the doctor can do prenatal screening tests.

A standard test such as an NIPT (noninvasive prenatal testing) is currently available and performed in the doctor's office any time from the 10th week of pregnancy onwards.

The blood test is quick and doesn't place any risk on the unborn child's life or development.

And, the results in most cases are available for review within 2 weeks. However, there is a small risk for a false positive.

Due to the complexity of PWS, if there's a greater chance that a person may be carrying a child with the syndrome, a DNA methylation analysis test can offer complete and accurate results to determine all the major genetic subtypes.

Another option for families is PGD, or preimplantation genetic diagnosis.

This is especially beneficial in cases where there is an imprinting center deletion of the chromosome 15 detected or familial translocation.

DNA Tests Currently Available for Prader Willi Syndrome Include:

There are currently four main tests available for testing. They include DNA methylation, FISH, chromosome microarray and uniparental disomy and imprinting defect testing.

Where Can I Go for a Genetic Test?

A doctor may do the blood test in the office or refer you to a specialist. Once the sample is available, it will go to a lab that specializes in PWS.

DNA Testing for Prader Willi Syndrome: Strengths and Limitations

Prader Willi Syndrome is a complex genetic disorder with multiple subtypes. Because of the complexity, a specialist needs to carefully examine the chromosome 15 to make a determination that's accurate.

Tests such as the DNA methylation and chromosome microarray have a very high percentage of accuracy, providing results that are, in most cases, true.

Unfortunately, no single test can provide 100 percent accuracy, leaving a small margin of error that may include a false-positive result.

Who does Prader Willi Syndrome Typically Affect?

Prader Willi Syndrome occurs randomly in roughly 1 out of every 15,000 births.

It can affect male or female infants or babies of any race or ethnic background.

If I Have a Child With Prader Willi Syndrome, What Are the Chances That Future Children Will Have it as Well?

Just because parents already have a child with PWS doesn't necessarily mean that the next child will have it, too.

In most cases — approximately 70 percent — a segment of the genes in chromosome 15 are missing and in nearly 25 percent of cases a child receives two copies of the chromosome, but only from the mother.

There are a very small percentage of cases where a genetic change to chromosome 15 is inherited. The risk to any future pregnancies depends on the genetic subtype of the child with PWS.

Can People With Prader Willi Syndrome Have Children in the Future?

In many cases if a woman has PWS they are infertile and thus unable to have children.

However, if the woman has it and is able to conceive, the deletion of a segment of the chromosome 15 on one of the two copies puts her at a 50 percent risk for passing on the Angelman disorder to her unborn child.

Likewise, if the father has PWS and has a deletion in the chromosome 15, the risk of passing on the genetic disorder to future offspring is 50 percent. This is because the mother's chromosome 15 is inactivated.

Prader Willi Syndrome Treatment Options

Treatment of the genetic disorder should begin as soon as the testing is complete and the diagnosis is confirmed 5.

The parents of young children or adults with PWS may have a team of specialists depending on the severity of the disorder.

This can include HGH treatments to help with growth and improve muscle tone, hormone treatments for children either at or approaching puberty, a dietician to monitor weight and teach parents or adults how to prepare healthy foods and portion sizes.

For infants with difficulty ingesting enough at each feeding, the pediatrician may change them over to a formula with a higher caloric intake.

Children and adults may also need to see a behavioral specialist or a mental health professional to learn how to best control their emotions.

The Prognosis for Prader Willi Syndrome

Early detection of the genetic disorder is essential in maintaining a better quality of life. Identifying it quickly allows parents or people with the disorder to make the necessary changes to their lives.

In children PWS can manifest in the form of obesity that then leads to many other mental and physical problems and diseases such as Type 2 diabetes and heart disease.

What Is the Life Expectancy of Someone With Prader Willi Syndrome?

A person who takes care of themselves and follows a strict diet can expect to live a full healthy life.

However, if a person who has the genetic disorder doesn't follow a strict diet they more than likely will become obese and as a result have many health problems in the future, some of which can be life-threatening.

Is There a Cure for Prader Willi Syndrome?

There is no cure at this time for Prader Willi Syndrome. However, having the disorder doesn't mean that a person can't live a normal, healthy life.

If they seek the available treatments and stick to a diet, they can manage the symptoms.

Scientists are currently working a form of gene therapy called CRISPR gene editing where they are aiming to activate the maternal chromosome.

It's in the early research stages of development and discovery.

What are Prader Willi Syndrome Care Options?

There are many treatment options available for people who have PWS.

Depending on the level of the genetic disorder a person may have an endocrinologist to treat hormones, a mental health or behavioral specialist, a dietitian to keep them at a healthy weight and a physical therapist.

Over time, if a person gets the help they need they can live both a full and productive life.

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Referenced Sources

  2. Prader-Willi syndrome.
    National Library of Medicine. June 11, 2019.
  3. diagnostic criteria.
  4. Prader-Willi Syndrome.
    National Center for Biotechnology Information. Retrieved online. 2019.
  5. Prader-Willi Syndrome.
    Daniel J Driscoll Jennifer L Miller Stuart Schwartz. Initial Posting: October 6, 1998; Last Revision: December 14, 2017.