Prader-Willi Syndrome

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What Is Prader-Willi Syndrome?

Prader-Willi syndrome (PWS) is a rare genetic disorder that is caused due to abnormal functioning of specific genes on chromosome 15.The condition is named after Swiss physicians Andrea Prader and Heinrich Willi and Alexis Labhart who described it in detail in 1950s. It is also called as Prader-Labhart-Willi, or Prader-Willi-Fanconi syndrome.

It is characterized by small hands and feet, abnormal growth and body composition (small stature, early-onset childhood obesity), hypotonia (weak muscles) at birth, hypogonadism, insatiable hunger, extreme obesity, and intellectual disability.

Prevalence and Etiology

Prevalence:

PWS affects an estimated 1 in 15,000 - 30,000 people. The prevalence rates differ among studies across countries, mainly due to using different methods for case identification. There is no strong evidence for increased risk in specific countries or gene pools. Both sexes appear to be affected equally.

Etiology:

People normally inherit one copy of each chromosome from each parent. Some of these genes are turned on (active) only on the copy that is inherited from a person's father (the paternal copy) which is called as genomic imprinting.

PWS is caused due to abnormality in the expression of genes on Chromosome 15 specifically on the long arm of chromosome 15q11-q13. This abnormality can be caused due to:

1. deletion of the genes on the paternal copy
2. the genes on the maternal copy are turned off (inactive)
3. has two copies of chromosome 15 inherited from the mother instead of one copy from each parent (maternal uniparental disomy)
4. chromosomal rearrangement called a translocation,
5. by a mutation or other defect (Imprinting center defects).

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