Thursday, May 2, 2013

PWS Awareness Day #2: The Three Subtypes of PWS

Did you know that there are three subtypes of PWS? 

Deletion (about 70% of cases; this is what Dean has) occurs when a small part of the paternal 15th chromosome is simply not present. We're talking about only 10 genes here. 

Uniparental disomy (UPD, about 30% of cases) occurs when there are two copies of the maternal 15th chromosome and no paternal 15th. That same portion of the paternal 15th that is absent in the deletion type doesn't do jack on the maternal 15th... so it's like it's not even there (following this?).

In a very small percentage of cases (less than 1%), there is an imprinting defect. Here, the genetic material is all present, but something causes that genetic material to be inactive (like turning a light switch to "off").

There are some differences between features of the three subtypes, but there are always many exceptions to the rule.

If you like to torture yourself with genetics, read more here:

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