PWS Awareness 2014: Day 7

Wednesdays: 9am IU 13 Physical Therapy

Today we will get a little scientific on you 🙂 Even I, three years into our PWS journey have trouble keeping this all straight, but it is important info…. Again taken from

What causes Prader-Willi syndrome?
PWS is caused by a lack of active genetic material in a particular region of chromosome 15 (15q11-q13). Normally, individuals inherit one copy of chromosome 15 from their mother and one from their father. The genes in the PWS region are normally only active on the chromosome that came from the father. In PWS, the genetic defect causing the inactivity of chromosome 15 can occur in one of three ways:

PWS by Deletion
Most often, part of the chromosome 15 that was inherited from the person’s father is missing, or deleted, in this critical region. This small deletion occurs in approximately 70% of cases and usually is not detectable with routine genetic analysis such as amniocentesis.

PWS by UPD (this is the type Siena has and can only be detected by a blood test called a methylation analysis, a FISH test can only identify deletions)
Another 30% or so of cases occur when an individual inherits two chromosome 15s from their mother and none from their father. This scenario is termed uniparental disomy (UPD).

PWS by Imprinting Mutation
Finally, in a very small percentage of cases, a small genetic mutation in the Prader-Willi region causes the genetic material (although present) in that area to be inactive.

Are there differences in the severity of PWS based on the genetic subtype?
There may be some subtle differences in the characteristics of PWS based on genetic subtype: those with deletions may be fair-skinned with light hair compared to other family members and may be more susceptible to seizures; those with PWS by UPD may be at higher risk for mental illness in young adulthood. Overall, however, there is considerable overlap between the different genetic subtypes. It is likely that the thousands of genes outside the PWS region, which exhibit normal variation between individuals, also contributes significantly to the variability in PWS symptoms between those with the disorder.



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