Sex Linked and Mitochondral Disorders Flashcards
What is the mean onset of BMD?
11 years.
How can the reading frame in DMD be corrected?
By using exon skipping.
How can the effect of muscular dystrophy be measured?
By measuring serum creatine kinase (reduces with muscular dystrophy).
What is X inactivation?
Why is it needed?
How does it happen?
- Since males and females need the same dosage of X-specific gene products, females must deactivate one X chromosome to compensate.
- Inactivation spreads from an X inactivation centre on the chromosome.
- The XIST gene maintains the inactivated state of the chromosome.
What is a Barr body?
An inactive X chromatin.
How do X linked dominant inheritance patterns differ from that of autosomal inheritance patterns?
1 - Excess of affected females.
2 - No male to male or male to female transmission.
List 3 X linked diseases.
Are they dominant or recessive?
Recessive:
1 - DMD.
2 - BMD.
3 - Congenital adrenal hyperplasia.
Dominant:
1 - Vitamin D resistant rickets.
Give an example of sex limitation.
Virilisation of female infants with congenital adrenal hyperplasia.
How many genes are contained within the mitochondrial genome?
37.
What is the collective function of the proteins produced by the genes of the mitochondrial genome?
They are components of the respiratory chain.
- Most mitochondrial proteins are produced from nuclear genes.
Why is mitochondrial inheritance exclusively maternal?
Because sperm mitochondria are actively expelled from the fertilised egg.
Why is mitochondrial inheritance said to show heteroplasmy?
Because if a mutation arises in mitochondrial DNA, it will create a mixed population of normal and mutated mitochondria within the cell.
What happens to the mitochondria of a cell upon mitosis?
They are split and randomly distribute among daughter cells.
List 7 characteristic features of mitochondrial disorders.
1 - Muscle weakness.
2 - Epilepsy.
3 - Deafness.
4 - Optic atrophy.
5 - Diabetes.
6 - Cardiomyopathy.
7 - Aplastic anaemia.
List 2 mitochondrial DNA disorders.
1 - Kearns-Sayre syndrome.
2 - MELAS.
What is the main sign of Kearns-Sayre syndrome?
Chronic progressive external opthalmoplegia (paralysis of the eye muscles).
What does MELAS stand for?
Mitochondrial encephalopathy with lactic acidosis and stroke-like episodes.
What is the significance of nuclear genes encoding most mitochondrial proteins?
Disorders of mitochondria don’t always result from mutations in mitochondrial DNA.
What is the threshold effect?
Phenotypic manifestation of the genetic defect occurs only when a threshold level is exceeded.
Why might an affected mother with a mitochondrial disorder produce offspring that do not express the phenotype (are carriers)?
- Due to the threshold effect.
- Heteroplasmy means the fertilised egg did not contain enough mitochondria to allow the phenotype to manifest.
