Prader-Willi syndrome is a genomic imprinting disorder caused by the failure to express SNRPN (small nuclear ribonucleoprotein-associated polypeptide N) gene product. SNRPN is expressed only on the paternal chromosome 15q11-q13, however, the exact genes responsible for Prader-Willi syndrome haven't been identified. People normally inherit one copy of chromosome 15 from each parent. Some genes are active only on the copy that is inherited from a person's father, the paternal copy. Genomic imprinting causes this parent specific gene activation.
The maternal SNRPN is methylated and not transcribed. The deletion of the paternal allele, which occurs in 70% of cases (this occurs when a segment of the paternal chromosome 15 is deleted in each cell), or maternal uniparental disomy (UPD), which occurs in 25% of cases, leads to loss of expression of SNRPN gene, and thus, to Prader-Willi syndrome. UPD causes the affected individual to have two copies of chromosome 15 inherited from their mother instead of one copy from each parent.
Prader-Willi syndrome can also be caused by a translocation, or by a mutation or other defect that inactivates genes on the paternal chromosome 15, however, this is very rare. …show more content…
Genes that provide instructions for making small nucleolar RNAs (snoRNAs) are among them. These snoRNAs have many functions, including helping to regulate other types of RNA molecules. Studies concur that the loss of a group of snoRNA genes, known as the SNORD116 cluster, may play a major role in causing the signs and symptoms of Prader-Willi syndrome. However, it is unknown how a missing SNORD116 cluster could contribute to behavioral problems, intellectual disability, and the physical features of the
The maternal SNRPN is methylated and not transcribed. The deletion of the paternal allele, which occurs in 70% of cases (this occurs when a segment of the paternal chromosome 15 is deleted in each cell), or maternal uniparental disomy (UPD), which occurs in 25% of cases, leads to loss of expression of SNRPN gene, and thus, to Prader-Willi syndrome. UPD causes the affected individual to have two copies of chromosome 15 inherited from their mother instead of one copy from each parent.
Prader-Willi syndrome can also be caused by a translocation, or by a mutation or other defect that inactivates genes on the paternal chromosome 15, however, this is very rare. …show more content…
Genes that provide instructions for making small nucleolar RNAs (snoRNAs) are among them. These snoRNAs have many functions, including helping to regulate other types of RNA molecules. Studies concur that the loss of a group of snoRNA genes, known as the SNORD116 cluster, may play a major role in causing the signs and symptoms of Prader-Willi syndrome. However, it is unknown how a missing SNORD116 cluster could contribute to behavioral problems, intellectual disability, and the physical features of the