GENETIC IMPRINTING

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GENETIC IMPRINTING

• A condition that depends on which chromosome
  (mother or father) bears the defect.

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Prader-Willi Syndrome

• Prader-Willi syndrome (PWS) is a genetic disorder
  that occurs in approximately one out of every
  15,000 births. PWS affects males and females with
  equal frequency and affects all races and
  ethnicities. PWS is recognized as a common
  genetic cause of childhood obesity. As babies,
  they tend to have poor muscle tone.
• The symptoms of Prader-Willi syndrome are caused
  by dysfunction of a portion of the brain called
  the hypothalamus. The hypothalamus is a small
  endocrine organ at the base of the brain that
  plays a crucial role in many bodily functions,
  including hunger and satiety, temperature and
  pain regulation, fluid balance, puberty,
  emotions, and fertility.

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• The problem is a deletion or abnormality on the
  paternal 15 chromosome.
• The risk of recurrence in a family is rare. The
  best estimate is said to be 1.

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Angleman Syndrome
Inheritance of the deletion from the mother on
chromosome 15 produces Angelman syndrome (note
the characteristic posture).
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• AS is characterized by intellectual and
  developmental delay, speech impediment, sleep
  disturbance, unstable jerky gait, seizures, hand
  flapping movements, frequent laughter/smiling and
  usually a happy demeanor.

Angelman syndrome affects an estimated 1 in
12,000 to 20,000 people.
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FRAGILE X

• Fragile X is the most common inherited cause of
  mental impairment and the most common known cause
  of autism.

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• Females carry the gene abnormality 2-4 times more
  often than males, but only about one third of
  females who carry the abnormal gene demonstrate
  decreased intelligence.
• Females with the disorder are more likely to have
  less impairment and less obvious physical
  characteristics. Males with the disorder are more
  likely to be sensitive to environmental factors.
• The pattern of inheritance most closely resembles
  X-linked dominance with variable penetrance.
  Occasionally, females are severely affected
  because of the complex genetics of the disorder.

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Karyotype of Fragile X