X-Linked Disorder and Mitochondrial Inheritance

Question 1

X-linked recessive

Answer 1

• females are carriers
• males are affected
• can skip generations
• sons of affected mothers have 50% chance of being affected and 50% daughters
• affected males don’t pass onto their sons but all females will be carriers

Question 2

examples of X-linked recessive disorders

Answer 2

haemophilia
colour blindness
muscular dystrophy

Question 3

impact of genetic technology

Answer 3

• improved strategies for assessment and diagnosis of females who may be carriers
• potential strategies for prenatal diagnosis
• safer therapeutic strategies

Question 4

pedigree analysis

Answer 4

• examine family tree
• provide probability
• not that sufficient

Question 5

lyonization

Answer 5

random inactivation of the maternal or paternal copy of x chromosome

Question 6

problems with phenotypic analysis

Answer 6

• requires fetal blood sample from prenatal diagnosis, therefore late and difficult
• variation in other factors e.g. exercise, diet, stress etc

Question 7

DNA analysis

Answer 7

• allows for a more accurate, timely and definitive diagnosis to be made
• DNA can be obtained from any nucleated cell
• can be analyzed by direct mutation analysis or indirect analysis (linkage)

Question 8

direct mutation analysis

Answer 8

where the mutation responsible for the condition is known

e.g. analysis DNA of affected patient

Question 9

indirect analysis

Answer 9

linkage or RFLP analysis
where the mutation is not known
- very rare

Question 10

problems with linkage analysis

Answer 10

• need family cases, both index and parents
• non-paternity (not the father)
• recombination
• Polymorphism / lack of informative marker

Question 11

options and process for females confirmed as a carrier

Answer 11

1. discuss probability of having an affected child
2. if she decides to have child, can analyze DNA obtained from fetal cells by CVS or amniocentesis
3. some families may decide to get preimplantation diagnosis (e.g. select females)

Question 12

mitochondrial DNA (mtDNA)

Answer 12

• double-stranded circular DNA
• no introns present
• maternally inherited
• greater risk for mutations
• disorders affect cardiac skeletal muscles and neuorological