What causes Prader-Willi syndrome?
Genes on chromosome 15 that lose function cause Prader-Willi syndrome. At conception, you inherit one copy of chromosome 15 from each of your biological parents. The paternal copy of chromosome 15 is the only one that activates or turns on. The maternal copy is turned off. Both copies are necessary for your genes to get the instructions your body needs to function. This process is called genomic imprinting. There are different causes of this genetic change to chromosome 15: Chromosomal deletion: Nearly 70% of all PWS cases occur when part of the paternal chromosome 15 is missing in each cell. Symptoms arise because the paternal copy of chromosome 15 is missing or not working properly and the maternal copy is turned off. Maternal uniparental disomy: About 25% of PWS cases happen when a child inherits two maternal copies of chromosome 15 instead of one from each biological parent. This means that both copies of chromosome 15 don’t work because they’re inactive. Translocation: Less than 1% of all cases occur when a piece of chromosome 15 relocates itself to another chromosome. This makes the genes that the chromosome produces work ineffectively since they’re not where they’re supposed to be. Chromosome 15 is responsible for providing instructions for making small nucleolar RNAs (snoRNAs). The job of snoRNAs is to regulate the function of other RNA molecules. RNA molecules create proteins that help cells complete many functions within your body. A change to chromosome 15 limits its ability to create snoRNAs or they don’t receive the instructions they need to complete their jobs correctly.