Lecture Notes on Genetic Imprinting and Related Syndromes

Introduction to Imprinting

• Imprinting is a key topic in the epigenetic section of medical resources such as First Aid.
• Understanding imprinting can provide easy points on exams like the USMLE and COMLEX.

What is Imprinting?

• Basic Concept: Imprinting involves gene silencing through methylation.
  • Methylated genes are "turned off."
  • Imprinting depends on whether the gene is maternally or paternally inherited.
• Phenotype Expression: The origin of the gene (mom or dad) determines the phenotype when one gene is turned off.

High-Yield Diseases Related to Imprinting

• Focus on two diseases linked to chromosome 15:
  • Prader-Willi Syndrome
  • Angelman Syndrome

Prader-Willi Syndrome

• Occurs when there's a deletion or methylation of the paternal gene on chromosome 15.
• Mnemonic: Paternal = Prader-Willi (both start with P).
• Key Symptoms:
  • Hyperphagia (excessive eating)
  • Obesity
  • Short stature
  • Hypogonadism (indicated by absence of visible testicles in the mnemonic picture)
• Mnemonic Imagery: Think "Darth Vader Willy" - short and fat.

Angelman Syndrome

• Results from deletion or methylation of the maternal gene on chromosome 15.
• Mnemonic: Maternal = Angelman (both have M's).
• Key Symptoms:
  • Inappropriate laughter (most high-yield symptom)
  • Seizures
  • Speech delay
• Mnemonic Imagery: An angel with a crown (seizures) and hands in front of mouth (speech delay).
• Buzzword: "Happy puppet" due to constant inappropriate laughter.

Summary of Key Points

• Deletion on chromosome 15 can be either paternal or maternal.
• Paternal: Prader-Willi Syndrome
  • Think "Darth Vader Willy"
  • Symptoms: Hyperphagia, obesity, short stature.
• Maternal: Angelman Syndrome
  • Think of a laughing angel
  • Symptoms: Inappropriate laughter, seizures, speech delay.

Conclusion

• Imprinting is an important topic with high exam relevance.
• Understanding the simple mnemonics and symptoms can lead to easy points on exam day.