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What is the Prader–Willi syndrome? – Part 1

• Prader–Willi syndrome is a rare genetic disorder.
• In this syndrome seven genes (or some subset thereof) on chromosome 15 (q 11–13) are deleted or unexpressed (chromosome 15q partial deletion) on the paternal chromosome.
It was first described in 1956 by:
• Andrea Prader (1919–2001)
• Heinrich Willi (1900–1971)
• Alexis Labhart (1916)
• Andrew Ziegler
• Guido Fanconi of Switzerland

Characteristics of Prader–Willi Syndrome

• Low muscle tone.
• Short stature.
• Incomplete sexual development.
• Cognitive disabilities.
• Problem behaviors.
• A chronic feeling of hunger.
• This can lead to excessive eating and life-threatening obesity.
• The incidence of PWS is between 1 in 25,000 and 1 in 10,000 live births.
• The paternal origin of the genetic material that is affected in the syndrome is important.
• This is because the particular region of chromosome 15 involved is subject to parent of origin imprinting.
• This means that for a number of genes in this region only one copy of the gene is expressed while the other is silenced through imprinting.
• For the genes affected in PWS, it is the paternal copy that is usually expressed.
• The maternal copy is silenced.
• This means that while most people have a single working copy of these genes, people with PWS have a non-working copy and a silenced copy.
• PWS has the sister syndrome Angelman syndrome.
• In this maternally derived genetic material is affected in the same genetic region.
• With the recent benefits of early diagnosis and ongoing interventions the obesity rate among children with Prader-Willi Syndrome has decreased.
• With behavioral therapy and other treatments, the effects of the syndrome can be reduced.

Signs and symptoms of Prader–Willi syndrome

– In utero
• Reduced fetal movement.
• Frequent abnormal fetal position.
• Occasional polyhydramnios (excessive amniotic fluid).

– At birth
• Often breech or caesarean births.
• Lethargy.
• Hypotonia.
• Feeding difficulties (due to poor muscle tone affecting sucking reflex).
• Difficulties establishing respiration.
• Hypogonadism.

– Infancy
• Failure to thrive (continued feeding difficulties)
• Delayed milestones/intellectual delay
• Excessive sleeping
• Strabismus (‘crossed eyes’)
• Scoliosis (often not detected at birth)
• Cryptorchidism

– Childhood
• Speech delay
• Poor physical coordination
• Hyperphagia (over-eating) from age 2 – 8 years
• Excessive weight gain
• Sleep disorders
• Scoliosis

– Adolescence
• Delayed puberty
• Short stature
• Obesity
• Extreme flexibility

– Adulthood
• Infertility (males and females)
• Hypogonadism
• Sparse pubic hair
• Obesity
• Hypotonia (low muscle tone)
• Learning disabilities/borderline intellectual functioning (but some cases of average intelligence)
• Prone to diabetes mellitus
• Extreme flexibility
• General physical appearance (adults)
• Prominent nasal bridge
• Small hands and feet with tapering of fingers
• Soft skin, which is easily bruised
• Excess fat, especially in the central portion of the body
• High, narrow forehead
• Almond-shaped eyes with thin, down-turned lids
• Light skin and hair relative to other family members
• Lack of complete sexual development
• Frequent skin picking
• Striae
• Delayed motor development

Prader-Willi Syndrome When a Gene Makes You Smell Like a Fish Psychiatric and Behavioural Disorders in Intellectual and Developmental Disabilities

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