Prader Willi Syndrome

Pradar Willi and Angleman Syndrome Website Lecture Group 3

Background

The Chromosome

Chromosomes are located in the nucleus of cells. They are what make up the genetic information that allows all organisms to be unique. Chromosomes consist of Deoxyribonucleic acid that are bundled up tightly to form the larger chromosome structure. In human cells there are usually 46 chromosomes. 23 inherited from the father called paternal and 23 from the mother called maternal. On the 46 chromosomes there are alleles that code for certain traits. If some allelic traits are not expressed (imprinted) can cause genetic disorders like Prader-Willi or Angelman syndrome (2013, Klug).

Prader-Willi Syndrome and Angelman Syndrome

Prader-Will and Angelman are two

Angelman and Prader-Willi syndromes are congenital diseases, present from birth, and are a result of chromosomal abnormalities. Two common proximal deletion breakpoint regions exist in both of the syndromes; this deletion mechanism is the same one that accounts for paternal and maternal deletions. PWS is caused by an absence of a paternal contribution in the chromosome 15q11.2–q13 region, while AS is due to an absence of a maternal contribution in the same region Leff et al. (1992) suggests that Prader-Willi syndrome is a result of missing genes on a maternal chromosome because of its association with parental gene deficiencies in chromosome 15q11.2–q13 region. Snrpn gene on a human chromosome 15q11–13 coding for a brain enrinched small nuclear ribonucleoprotein (snRNP)-associated polypeptide SmN was mapped to chromosome 7 in mouse (Leff et al, 1992).This experiment established that Snrpn is a maternally imprinted gene in mice. These studies, in combination with the associated human mapping studies showing that SNRPN maps in the Prader−Willi critical region, show the importance of the SNRPN gene, its involvement in PWS and suggest that one of the causes of PWS may be because of defects in mRNA processing. This experiment provided evidence that snRPN is an imprinted gene in a maternal chromosome in mice. Other human mapping studies that

These compounds are thought be involved in the regulation of other RNA molecules and expression of signs and symptoms of Prader-Willi syndrome. People with Prader-Willi syndrome may present with an unusually fair skin and light-colored hair if they lose a gene called OCA2 on the region of chromosome 15. It codes for proteins involved in determination of skin, hair, and eyes pigmentation and does not result in other signs and symptoms of this disorder (Cassidy et al, 2000).

Angelman syndrome is triggered by a change that occurs on the same chromosome as Prader-Willi syndrome, that is chromosome 15(q11-q13) but a on a different specific region. According to Adams (2008), there are at least four known mechanisms that results in Angelman syndrome and these include chromosome deletion, paternal uniparental disomy (UPD), ubiquitin-protein ligase E3A (UBE3A) mutation, and imprinting center