Prader-Willi Syndrome
Prader-Willi syndrome (abbreviated PWS) is a very rare genetic disorder, in which seven genes (or some subset thereof) on chromosome 15 are missing or unexpressed (chromosome 15q partial deletion) on the paternal chromosome. It was first described in 1956 by Andrea Prader, Heinrich Willi, Alexis Labhart, Andrew Ziegler, and Guido Fanconi of Switzerland. The incidence of PWS is between 1 in 10,000 and 1 in 15,000 live births. The distinction of chromosome by paternal origin is due to imprinting and PWS has the sister syndrome Angelman syndrome that affects maternally imprinted genes in the region.
Prader-Willi Syndrome Diagnosis
PWS affects approximately 1 in 10,000 to 1 in 15,000 newborns. There are more than 400,000 people who live with PWS around the world. It is characterized by hypotonia, short stature, polyphagia, obesity, small hands and feet, hypogonadism, and mild mental retardation. This so-called PWS/AS region may be lost by one of several genetic mechanisms which, in the majority of instances occurs through chance mutation. Other less common mechanisms include; uniparental disomy, sporadic mutations, chromosome translocations, and gene deletions. Due to imprinting, the maternally inherited copies of these genes are virtually silent, only the paternal copies of the genes are expressed. PWS results from the loss of paternal copies of this region. Deletion of the same region on the maternal chromosome causes Angelman syndrome (AS). PWS and AS represent the first reported instances of imprinting disorders in humans.
The risk to the sibling of an affected child of having PWS depends upon the genetic mechanism which caused the disorder. The risk to siblings is <1% if the affected child has a gene deletion or uniparental disomy, up to 50% if the affected child has a mutation of the imprinting control region, and up to 25% if a parental chromosomal translocation is present. Prenatal testing is possible for any of the known genetic mechanisms.
Studies of human and mouse model systems have shown that deletion of the 29 copies of the C/D box snoRNA SNORD116 (HBII-85) has been shown to be the primary cause of Prader-Willi syndrome.
Prader-Willi Syndrome Neuro-cognitive
Individuals with PWS are at risk of learning and attention difficulties. Curfs and Frym (1992) conducted research into the varying degrees of learning disability found in Prader Willi Syndrome (PWS). Their results were as follows:
- 5%: IQ above 85 (average to low average intelligence)
- 27%: IQ 70 – 85 (borderline intellectual functioning)
- 34%: IQ 50 – 70 (mild intellectual disability)
- 27%: IQ 35 – 50 (moderate intellectual disability)
- 5%: IQ 20 – 35 (severe intellectual disability)
- <1%: IQ <20 (profound intellectual disability)
Cassidy found that 40% of individuals with PWS have borderline/low average intelligence, a figure higher than that found in Curfs and Frym's study (32%).
Auditory information processing and sequential processing are relatively poor, as are arithmetic and writing skills, visual and auditory short term memory and auditory attention span. These sometimes improve with age, but deficits in these areas remain throughout adulthood.
Because of severe obesity, obstructive sleep apnea is a common sequela, and a positive airway pressure machine is often needed.
This article is licensed under the Creative Commons Attribution-ShareAlike License.
It uses material from the Wikipedia article on
"Prader-Willi Syndrome"
All material adapted used from Wikipedia is available under the terms of the
Creative Commons Attribution-ShareAlike License.
Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.