X-Linked Disorders

Question 1

• Characteristics? (2)
• Recessive characteristics?
• Dominant characteristics?
• May affect expressivity?

Answer 1

• Mostly males effected, no male to male transmission
• Males have it and women are carriers
• Expressed in females and males
• X inactivation

Question 2

Recessive Examples:

1. ) Duschenne Muscular Dystrophy:
   - Gene affected?
   - Phenotype?
   - Test for it?
2. ) Beckers:
   - Onset?
   - What causes it?
3. ) DCD assoc. DCM:
   - Caused by?
   - Clinical presentation?

Answer 2

• DMD (Dystrophin)
• Muscles weakness prox.>distal, calf hypertrophy, dilated cardiomyopathy
• Gower maneuver
• Later onset
• Abnormal quantity or quality of dystrophin
• No dystrophin in myocardium
• Cardiomyopathy without skeletal involvement

Question 3

4. ) Hemophilia A:
   - What causes it?
   - Phenotype?
5. ) Fragile X:
   - Caused by?
   - Protein affected?
   - Phenotype?
   - Range of repeats?

Answer 3

• F8 deficiency (inversion of 22)
• Bleeding into joints, muscles cranium; excessive bruising
• CGG repeats (maternal anticipation)
• Cognitive defects, autism, dysmorphic features, aggression
• 200 full mutation

Question 4

Mitochondrial DNA:

• Found where?
• Type of effect?
• Heteroplasmy?
• Homoplasmy?
• Ex? (4)

Answer 4

• Where ATP is abundant
• Threshold effect
• Mutated and normal in same mito.
• Only mutated or non
• Kearns Saye, MELAS, MERF; Leber Optic Neuropathy