This week is PWSA UK Awareness Week. The Prader-Willi Syndrome Association UK want to spread the word about the rare chromosome disorder. They want more people to know about the syndrome, in an effort to allow children and adults with PWS to be understood and accepted, and to make more people across the country aware of what the condition means for PWS people and their families, friends, and carers.
About 70% of all cases of PWS are where - with no known explanation - the critical PWS section of chromosome 15 (or The Bastard Bit Of The Bastarding Bastard, as I like to call it) is missing. The section has disappeared, and there’s no rhyme or reason to it. (Although a rhyme would be pretty rubbish: ‘It’s a paternal deletion, our blinds are Venetian’. See?). The deletion is inexplicable, and there is a less than 1% chance of it happening in another pregnancy. This is the genetic reason for my daughter’s PWS.
Yes, this sounds like a Peel Session. “A great live track from Maternal Uniparental Disomy there - three more from them later...”. UPD is a less common form of PWS (about 25% of cases are caused by it), and it is where the baby inherits both copies of chromosome Bastarding Bastard from the mother. Even though there are two complete copies of the chromosome, the key genes are imprinted - ‘turned off’ - resulting in PWS. This has the same effect as a deletion. Again, there is very little chance of this happening again in a further pregnancy (in fact, it never has).
In very rare cases (less than 5%), the PWS genes on the father’s chromosome are there, but do not work because his imprinting process is faulty. Chromosome 15 has a tiny little control centre (imagine the bridge of the Starship Enterprise), which is responsible for ‘switching on’ all its genes. When there is a tiny defect in the imprinting control centre, the PWS section may not be switched on correctly. (Imagine if Captain Kirk accidentally knocked out a power lead when having sex with a green alien woman while his shipmates were in the canteen. That sort of thing). An imprinting defect can appear suddenly, or can be present in the father’s chromosome he received from his mother. If the latter is the case, then there is a 50-50 chance that any child he has will receive the defective chromosome, because, crucially, the defect has now crossed to the father’s side. Further testing and genetic counselling are hugely important for families with a child whose PWS is caused in this way.
So, I hope I’ve made that all clear. References to Snow White and Star Trek may or may not have helped. I don’t think a quick burst of Heigh Ho! or a panic about the reoccuring shortage of dilithium crystals has anything to do with Prader-Willi. Although an urge to be beamed to another planet does occasionally cross my mind.
Please note: most* (*all) of the facts on this page have been heavily influenced* (*stolen) from the Genetics Of Prader-Willi Syndrome section of the Prader-Willi Syndrome Association USA's website. To read the original, more detailed, and much more sensible article, click here.
Video is Mull Historical Society - Minister For Genetics And Insurance MP