Pedigrees and Risk Flashcards
Why do we measure the risk of genetic conditions instead of scanning for the gene
- Many diseases mix of familial and sporadic
- Many causative gene isn’t known
- Impossible to test every one for disease genes
- When disease exclusively familial and mutation known many do not want test - various reasons - often that they would live with hope and uncertainty.
- > 80% of people with 50% risk of being carrier Huntingdon’s disease decline test
What is the proband
The person who initially presents with the disease
How to know it is autosomal dominant from a pedigree diagram
Vertical transmission down generations where not all offspring are affected, but you need to have at least one affected parent. Males and females are equally affected
Why do autosomal dominant diseases occur
Mutated gene affects the normal function of normal gene at protein level or gain new function. Both sexes have 2 of each autosome so 50% chance of inheritance
Complicating factors of genetic diseases
Age of onset
Some get worse with age and there are more mutations
How to tell X linked recessive from a diagram
- Passed through generations without affecting people
- Only affected males
- Passed on through an unaffected mother
Not all offspring or all generations are affected
How to tell a mitochondrial disease from a diagram
- All offspring of affected mothers are affected
- Vertical transmission
- Not inherited from affected father
All generations affected
How to tell autosomal recessive from genetic tree
Usually no family history
Parents unaffected
Horizontal transmission-siblings and cousins are affected
Not all offspring affected
Males and Females affected
Possible consanguinity - those two become obligate Carriers because they have two children with it
What is risk
Predicted chance of having disease or being the carrier
