FAQs

Q. Does my child have Prader-Willi syndrome?
Q. How is Prader-Willi syndrome diagnosed?
Q. Are there different types of Prader-Willi syndrome?
Q. Is Prader-Willi syndrome hereditary?
Q. Why did Prader-Willi syndrome happen to us and could it have been prevented?
Q. Is there a cure for Prader-Willi syndrome?
Q. Will my child have all the characteristics of Prader-Willi syndrome?
Q. What is the life expectancy of someone with PWS?
Q. Will my child be able to have their own family?
Q. Will my child be able to live independently?
Q. Are there similar disorders to PWS and is a misdiagnosis possible?
Q. PWS behaviours are often described as being similar to those in Autism Spectrum Disorder(ASD) – do individuals with PWS also have ASD?

Q. Does my child have Prader-Willi syndrome?
If your newborn has unexplained low muscle tone (is floppy) and has a poor suck reflex causing feeding difficulties, your doctor should test for PWS. The PWSA(NZ) can help if you have any questions or if you are experiencing difficulties with getting your child tested. If your child is older, the feeding difficulties would have improved over time, but if low muscle tone persists and your child starts to present with global developmental delay (reaching milestones later than peers) and then later with weight gain, increased appetite or cognitive disabilities, these are further reasons to request testing. The clinical diagnostic criteria that doctors should use are available on our diagnosis page.

Q. How is Prader-Willi syndrome diagnosed?
Doctors should test for PWS using a blood test known as methylation analysis because this will detect all genetic subtypes of PWS in over 99% of cases. A blood test known as a ‘FISH’ test only identifies PWS by deletion. Additional blood tests may be necessary to further determine genetic cause.

Q. Are there different types of Prader-Willi syndrome?
Yes, PWS has 3 genetic causes which all result in deleted or unexpressed genes in the same region of chromosome 15. There are subtle differences between the subtypes with no feature found exclusively in one group. It is important to recognise that even within a genetic type there is a lot of variation among people affected with PWS. For example, even though those with uniparental disomy (UPD) as a group have a slightly higher mean intelligence quotient (IQ) than those with deletion as a group, there is a very wide range of IQ within each genetic group. It is also important to remember that individuals with PWS have inherited all their chromosomes from their parents and will present with other family traits. Therefore, knowing the genetic type is not very helpful in knowing the future abilities or difficulties of the individual.

As a group, those with a deletion are more likely to have fair colouring (hair, eyes, skin), whereas those with UPD more closely resemble their parents. Individuals with a deletion are more likely than those with UPD to have the characteristic facial appearance of PWS and they are more likely to be skilled with jigsaw puzzles.
As a group, those with UPD are more likely to be born late. As noted above, they have a slightly higher average IQ than the group with deletion. In addition, they tend to have somewhat milder behavioural difficulties. However, it appears that people with UPD as a group have a significantly higher incidence of autistic characteristics and of mental health issues than those with deletion. In rare cases, UPD can occur as a result of isodisomy (a maternal chromosome is duplicated and 2 identical chromosomes are inherited) rather than the usual heterodisomy (2 non-identical maternal chromosomes are inherited) and this may affect severity of symptoms.
Individuals with an imprinting defect appear to be most similar to those with UPD.
In addition to these differences, there are some studies suggesting somewhat increased behavioural difficulties in those with a Type 1 (slightly larger) deletion versus those with a Type 2 deletion. There are also some studies that have not shown these differences.

Q. Is Prader-Willi syndrome hereditary?
In the majority of cases there is no increased recurrence risk as there is no specific risk associated with PWS by deletion or uniparental disomy (UPD), except in the rare case of a chromosomal balanced rearrangement or translocation present in either parent. However, PWS can reoccur if the genetic cause is an imprinting defect, if the defect is present in the father’s chromosome inherited from his mother (risk = up to 50%). There is also a smaller recurrence risk with a rare type of deletion caused by ‘chromosomal translocation’ (a chromosomal rearrangement when part of one chromosome breaks and attaches to another.) Parents of children with these genetic types and other family members may wish to commence genetic counselling if planning more children.

Q. Why did Prader-Willi syndrome happen to us and could it have been prevented?
There is nothing either parent did to cause Prader-Willi syndrome occurring and there is no way to prevent it. Scientists do not know why these chromosome alterations occur either during the formation of egg or sperm cells or at conception. The only finding is related to the likelihood of PWS occurring by uniparental disomy, which is that it is more likely to occur in older mothers than younger mothers. This is because older eggs are more likely to have errors types such as extra chromosomes. 

Q. Can Prader-Willi syndrome be detected before birth?
Fetal growth restriction, reduced fetal movements and excess amniotic fluid are features commonly diagnosed during pregnancy, particularly during the third trimester. Some babies have also been noted to have subtle, immobile malpositions of the extremities, with extended feet and flexed toes or clenched fists during ultra-sound scans.  However, none of these symptoms are limited to Prader-Willi syndrome and rarely alert clinicians to the possibility of a PWS diagnosis. If there is a considered risk for PWS or genetic abnormality, prenatal testing is usually offered. A CVS test using a placental blood sample can be done between 11-13 weeks and is mostly accurate, particularly if a specific genetic disorder is being tested for. An amniocentesis test is usually performed between 15-20 weeks but carries a higher risk of miscarriage. Non-invasive prenatal tests have been available for some time for other genetic disorders, but they are now able to screen for microdeletions, including PWS. Therefore, a NIPT test will only detect PWS by deletion. It can be performed from 10 weeks using a maternal blood sample and is a safe and accurate screening test rather than diagnostic test. NIPT testing is now available in NZ, but is not yet publicly funded.

Q. Is there a cure for Prader-Willi syndrome?
There is no cure for PWS but with early diagnosis, appropriate support and treatment, people with PWS can live healthy, happy lives. Growth hormone treatment improves body composition and is available for all children diagnosed with PWS in New Zealand today. In conjunction with dietary control and exercise, growth hormone helps to maintain a healthy weight. Growth hormone can also improve motor development, cognition, speech, bone mineral density, mental health, quality of life, and these benefits increase with earlier treatment. If needed, other treatments may be provided for specific symptoms, such as sleep disorders, sleep apnoea, behaviour, hormone abnormalities and scoliosis.

Researchers are currently investigating dietary interventions for PWS and trials are underway exploring other possible therapies and treatments for PWS. Some of those currently raising hope within the PWS community are oxytocin, vagus nerve stimulation and various drug treatments for hyperphagia (hunger) or weight loss. Scientists working in the new field of genetic therapy are also seeking to activate the ‘silent’ genes on the maternal chromosome 15.

Q. Will my child have all the characteristics of Prader-Willi syndrome?
Not necessarily; all children with PWS are individuals who are affected by PWS differently. The characteristics seen in newborns are typical in most cases, although there are occasional cases of PWS which are not diagnosed until later because the child did not display many typical characteristics during infancy. Then, as a child grows, differences between individuals become more apparent. Some children may be more severely affected by one characteristic but mildly affected by another, for example, they may have less delay in reaching physical milestones, but have a high food seeking drive. PWS is a complex spectrum disorder so the severity of characteristics are often unrelated.

In addition to the typical characteristics of PWS, there are other symptoms you will read about which only occur in some people with PWS. These symptoms are not ‘typical’ of PWS but occur in the PWS population more frequently than in the general population and some are more common than others. These are symptoms such as sleep disorders, scoliosis and mental health disorders. Knowledge of these possible symptoms can help with identifying and treating them earlier, but it is best to take a ‘wait and see’ approach rather than assume your child will develop every symptom associated with PWS, which is very unlikely.

Q. What is the life expectancy of someone with PWS?
Providing appropriate dietary management strategies are put in place, the person leads a healthy lifestyle and receives good healthcare, their life expectancy should not be different to the general population.

Q. Will my child be able to have their own family?
People with PWS want to have relationships just like everyone else. These are often difficult to maintain due to poor social skills and behaviour issues, but long lasting relationships can be achieved with sufficient support. However, it was generally thought not possible for men or women with PWS to have children. To date, there are no known cases of a man with PWS fathering a child, but there have been a handful of cases of live births to women with PWS. If fertile, a woman with PWS by deletion has a 50% chance of their baby being born with Angelman syndrome, and if a man with PWS by deletion were to father a child, there is a 50% chance their baby would have Prader-Willi syndrome. If fertile, those with PWS by UPD would have every chance of having a healthy baby.

Q. Will my child be able to live independently?
There are very rare cases of people with Prader-Willi syndrome who have been able to live independently, with a good support network around them. However, regardless of their cognitive functioning level, almost all adults with PWS require some degree of supported living because of the inability to control food intake. We live in hope that future research will lead to treatments for hyperphagia and will enable adults with PWS to live more independent lives. Help is often needed in other areas of life, but with appropriate support, people with PWS have been known to achieve many things, from university degrees to sports achievements to motivational speaking. With the right educational, employment and community support, adults with PWS are able to live meaningful and full lives.

Q. Are there similar disorders to PWS and is a misdiagnosis possible?
The methylation analysis test will detect PWS in over 99% of cases. It also distinguishes between PWS and Angelman syndrome because AS is also the result of a chromosome 15 abnormality, but with missing genes occurring on the maternal chromosome 15. (Angelman syndrome is sometimes referred to as a ‘sister syndrome’ to PWS although the characteristics are actually quite different.) There have been rare cases of methylation analysis producing a false positive result and, although very unlikely, it’s also possible that laboratory errors could occur and test results could be misread. If a patient diagnosed with PWS is not presenting with any typical characteristics of PWS, or if PWS is still suspected after a negative result, it is advisable to pursue repeat testing and the use of alternative genetic testing methods. In extremely rare cases, genetic mosaicism may occur in PWS which means a person may present with atypical symptoms which may not be recognised as fitting the PWS phenotype. It’s also possible for a person with mosaic form of PWS to present with some symptoms of both PWS and AS. It’s also very rare for PWS to occur alongside other genetic conditions which may exclude PWS from being considered, but the chance of this happening is increased in PWS by UPD.

If a patient is presenting with both obesity and delayed or altered intellectual development as major symptoms, alternative genetic conditions that could be considered are: Albright hereditary osteodystrophy, Alstrom syndrome, Bardet-Biedl syndrome, Borjeson-Forssman­Lehmann syndrome, Cohen syndrome and fragile X syndrome. There is also an increased prevalence of obesity in Down, Klinefelter and Turner syndromes. Obesity has also been linked to Leptin deficiency and MC4R gene mutations.

Schaaf-Yang syndrome was identified in recent years and closely resembles PWS. It’s a very rare, genetic disorder caused by a disruption of the MAGEL2 gene on chromosome 15, which is also missing in PWS. Schaaf-Yang syndrome shares many features with PWS including hypotonia, feeding difficulties during infancy, global developmental delay /intellectual disability, short stature, hypogonadism and sleep apnoea. However, patients with SYS have a much higher prevalence of autism spectrum disorder (approx 75%) whilst hyperphagia and obesity are far less commonly seen (approx 23%). Another difference is that joint contractures are also very common, typically affecting the finger joints, but in more severe cases also involving knees and elbows. Magel 2 research is ongoing.

Q. PWS behaviours are often described as being similar to those in Autism Spectrum Disorder(ASD) – do individuals with PWS also have ASD?
There is some overlap between these disorders and past estimates have indicated that of those individuals with PWS tested for ASD, 20-30% will receive a dual diagnosis of PWS and ASD (A prevalence of 26.7% calculated by review of published literature: Bennett, Germani, Haqq, Zwaigenbaum, 2015). However, PWS experts believed that prevalence rates of ASD and PWS have been overestimated due to limited data and questionable screening so they conducted a large cohort study of 146 individuals and clinically evaluated the participants using standard ASD measures. They found the rate of ASD and PWS to be 12.3%, much lower than previously thought. They also confirmed that the prevalence rate is higher amongst those with PWS by UPD or imprinting defect, approx. 25% and 28% respectively. (Dykens EM, Roof E et al, 2017)

It is clear that genetics can play a role in why autism occurs, but cause and genetic involvement is complex and not yet fully understood. However, some of the potentially involved genes can be found in the PWS region of chromosome 15, in particular the GABA receptor genes (a brain chemical – inhibitory neuro-transmitter) and the UBE3A genes of the maternally expressed chromosome 15. Also on chromosome 15, small genetic molecules known as non-coding RNAs influence gene expression and may regulate expression of a specific serotonin receptor gene (not located on chromosome 15) which may also be involved in ASD.

PWS and ASD are quite different disorders but there are some similarities in the areas of anxiety, sensory sensitivity, repetitive behaviours, preference for predictability, rigid thinking, emotional control, social functioning and communication difficulties. Dykens et al found that the repetitive behaviours of compulsivity and insistence on sameness were seen in 76-100% of their entire study group, particularly in routines, events, timing, repetitive questioning, becoming upset if interrupted, hoarding and ordering and arranging items. These behaviours did not correlate to IQ but impeded adaptive functioning (day to day living skills.) Restricted interests and stereotypies (mechanical/rhythmic, persistent movements or utterances) were unusual in the group with a PWS only diagnosis. Dykens et al also found that 45-70% of the PWS only group had some degree of impairment in sustaining conversations and in the quality and amount of their reciprocal social interactions. As a result of the similarities between PWS and ASD, many of the management techniques that work well for ASD also work well for PWS. Therefore, as teachers and carers are likely to be more familiar or experienced with management strategies for autism spectrum disorders, asking them to implement these for someone with PWS can be useful when time or resources don’t allow extensive PWS training. The similarities also mean that treatments trialled for ASD may also work for PWS. Oxytocin treatment is being actively studied as a treatment for ASD as well as in Prader-Willi syndrome. Nutrient and ‘gut health’ therapies sometimes used for ASD can also prove beneficial in PWS.