Clinical Genetics - Basics Flashcards
What three factors govern the balance of genetic and environmental factors for any condition?
100% Environmental
Polygenic
Single Gene
(represented as a triangle with environmental at the top)
What is achondroplasia?
Achondroplasia is a common cause of dwarfism, caused by a mutation in fibroblast growth factor receptor 3 (FGFR3)
What are the characteristics of a purely genetic cause of disease?
Rare
Simple genetics
Unifactorial
High recurrence rate
What are the characteristics of environmental cause of disease?
Common
Complex genetics
Multifactorial
Low recurrence rate
What categories are genetic disorders classified into?
Multifactorial/Complex Single Gene Chromosomal Mitochondrial Somatic Mutations
Define multifactorial/complex genetic disorders
Interaction of multiple genes in combination with environmental factors
Define single gene disorders
A mutation in a single gene
Define chromosomal genetic disorders
An imbalance or rearrangement in chromosome structure i.e. aneuploidy
Define mitochondrial genetic disorders
Due to mutations in the mitochondria DNA
Define somatic mutations
Mutations with a gene in a defined population of cells that results in disease
What are the 4 single gene modes of inheritance?
Autosomal Dom
Autosomal Rec
X-Linked
Mitochondrial
How many chromosomes are there?
46 in 23 pairs
What are the characteristics of gametes?
Contain 23 chromosomes with 1 copy of each gene
What would the following nomenclature mean about the patient?
AA
Healthy patient with 2 normal genes
What would the following nomenclature mean about the patient?
Aa
Healthy person with 1 normal copy and 1 gene copy with the disease mutation i.e. carrier
What are some characteristics of AD Inheritance?
A trait or disease runs from one generation to the next
Males and females are equally affected
Offspring of affected person has a 50% (1in2) chance of inheriting the mutation
What type of inheritance does the following relate to?
‘Affected individuals are heterozygous for the mutation
Autosomal Dominant
What type of inheritance does the following relate to?
‘Chance that the offspring affected = 50%’
Autosomal Dominant
What is ‘Penetrance?’
The frequency with which a specific genotype is expressed by those individuals that possess it, usually given as a percentage
What is incomplete penetrance?
Not all relatives who inherit the mutation develop the disorder
What is ‘Expressivity’
Variation in expression - the extent to which a heritable trait is manifested by an individual
What is ‘Anticipation’
The symptoms of a genetic disorder become apparent at an earlier age as it is passed fro one generation to the next
What is a ‘new dominant/de novo mutation’
A new mutation that has occurred during gametogenesis or in early embryonic development
What are some characteristics of AR inheritance?
Disease seen in one generation
Does not tent to pass from one generation to the next
Offspring of affected individuals has low risk of disease
Relatives may be asymptomatic carriers of the disease
M=F
Gene mutation, not chromosomes
