Basic information for topics, such as “What is it?” is available in the About Prader-Willi Syndrome section. Answers to other frequently asked questions (FAQs) specific to Prader-Willi Syndrome are in this section.
PWS could affect the offspring of someone with the syndrome, depending on how the individual developed the disorder and the individual's sex. The offspring could be at risk of being born with PWS or with Angelman syndrome. Angelman syndrome, like PWS, results from defects in one region of chromosome 15. The two syndromes both involve missing or silenced genes in this region, called the Prader-Willi critical region (PWCR). This section of the chromosome is "imprinted," and the genes involved in Angelman syndrome and PWS have different sex-specific imprinting patterns. This is the reason why the sex of the parent with PWS affects which disorder the offspring is at risk to inherit.
Read more about the imprinting, the PWCR, and the genetics of PWS.
- If a mother with PWS developed the syndrome because of the deletion of a section of one of her two copies of chromosome 15, her child will have a 50% risk of being born with Angelman syndrome. That is, if the mother with PWS passes on her chromosome 15 with the deletion, the child will have Angelman syndrome. This is because the father's genes in this region that are linked to Angelman syndrome are normally inactivated; thus, the child will have no active copies of these genes, causing Angelman syndrome. If the mother passes on her normal copy of chromosome 15, the child will not be born with Angelman syndrome or PWS.
- In the case of a father with PWS who has a deletion in chromosome 15, there is a 50% chance that he will pass on the affected chromosome to his child, leading to PWS. This is because a mother's genes that are linked to PWS are normally inactivated; thus, the child will have no active copies of these genes.
Because fertility is so rare in individuals with PWS, only one case of a mother with a deletion passing on Angelman syndrome to her child has been reported. No cases have been reported of a father who had PWS because of a deletion passing on PWS to his child, but it is possible.2
No case of either syndrome in the child of an individual with PWS through uniparental disomy (two copies of chromosome 15 from the mother and none from the father) has ever been reported, but they are theoretically possible. Inheritance could happen in three different ways, but all require the parent with PWS passing on both copies of his or her chromosome 15, which is unlikely.
- If the offspring also receives a copy of chromosome 15 from the other parent and none of these three copies is lost, this condition will be fatal before birth.
- If the parent with PWS is the mother and the offspring ends up with only two copies of chromosome 15 during development, the child will probably be born with PWS because he or she has inherited two inactivated copies of the genes in the PWCR.
- If the parent with PWS is the father and the offspring ends up with only two copies of chromosome 15 during development, the child will probably be born with Angelman syndrome. This is because the genes related to Angelman syndrome in the chromosome inherited from the mother are inactivated, and thus the child does not have any working copies of these genes, causing Angelman syndrome.2
Imprinting Center Defect
No cases have been reported of a parent who has PWS because of an imprinting center defect passing on PWS to his/her child. However, there is a theoretical possibility of this happening.2
- Åkefeldt, A., Törnhage, C. J., & Gillberg, C. (1999). A woman with Prader-Willi syndrome gives birth to a healthy baby girl. Developmental Medicine & Child Neurology, 41, 789-790. Retrieved June 13, 2012, from https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-8749.1999.tb00542.x
- Cassidy, S. B., & Schwartz, S. (1999). Prader-Willi syndrome. In Pagon, R. A., Birth, T. D., Dolan, C. R., Stephens, K., Adam, M. P. (Eds.). Gene reviews. Seattle, WA: University of Washington. Available from http://www.ncbi.nlm.nih.gov/books/NBK1330/