Molecular pathology: consequences of gene mutations at gene regulation level Flashcards
When is a DNA sequence change pathogenic?
Deletions, nonsense, and frameshift mutations are pathogenic mutations.
What is a polymorphism?
Sequence variation
Not all are pathogenic
When is a missense mutation more likely to be pathogenic?
When it affects a functionally important part of the protein.
If the amino acid is a conserved over evolution it is more likely to be important
If amino acid substitutions are non-conservative (polar for non polar, acidic for basic) they are more likely to be pathogenic.
What is an important part of a missense mutation that must be identified?
How severe the effects of the missense mutation are.
What is a loss of function mutation?
When there is a total loss of function resulting from total absence of the protein
Caused by any mutation which results in inactivation of the protein giving the same clinical result.
What type of activity does the ATM gene have?
Has a PI-3 kinase like domain
Therefore acts as a kinase phosphorylating other protiens (signalling protein)
How does the ATM kinase activity come about?
Has to be induced by DNA damage
How can ATM kinase activity be measured?
Immunoprecipitate the ATM protein using an ATM Ab and use it to phosphorylate a protein target (P53) in vitro.
Use a phosphospecific antibody
What do phosphospecific antibodies do?
Recognise the phosphorylated proteins but not the unphosphorylated formats.
What occurs to activity if proteins over time?
The activity changes over time
eg. ATM activity of phosphorylation increases over time
Other kinases can also phosphorylate ATM targets
What causes band shifts in data?
When a phosphorylated protein has a new molecular weight due to its phosphorylation.
What are some possible consequences of mutant ATM protein?
May have some retained function:
Allowing some degree of normal response to radiation
Could affect level of radiosensitivity -measurable
Gain of function
Altered interactions with other proteins
Give a consequence of having residual activity of ATM protein?
Increasing level of chromosome damage with decreasing ATM kinase activity.
ATM mutation causing cancer
What is Haploinsufficiency?
For most gene products, half the amount of protein is sufficient for normal function.
For other gene products, 50% of the normal level is not enough for normal function and haploinsufficiency produces an abnormal phenotype
What are dominant negative effects on alleles?
A non-functional mutant polypeptide can interfere with a normal protein from the normal allele gibing a dominant negative effect.
What conclusions can be drawn when there is no protein expression at all of prognosis?
Associated with classical disease
Leads to classical deteriation
What conclusions can be drawn when there is some protein expression for prognosis?
May be associated with a less severe form of the disease.
Difficult to suggest to a patient this will mean a better prognosis.
Need a lot of data
Why is cystic fibrosis a very variable disease?
Due to the influence of modifying genes and how other proteins are interacting within the mechanisms.
What evidence is there for possible modifying genes in ataxia telangiectasia?
No neurodegeneration when there is no ATM protein present.
What is locus heterogeneity?
Where the same disease can be caused by a mutation in a different gene.
What is hMRE11?
An essential gene which is required for life
What is the best candidate approach?
Where you test for other possible candidates leading to the dysfunction of a gene when the original idea mutation is not the cause
