Gene Scanning Flashcards
In what instances are gene scanning used?
- testing disorder with extensive allelic heterogeneity
2. families are likely to carry “private mutations” that are unlikely to be on a panel
4 possible results of gene scanning:
- disease causing mutation
- normal variant
- variant of undetermined significance
- negative result (normal sequence)
Used to size the entre genome for microdeletions
Microarray
What will a CGH array detect?
Deletion or duplication
How does obtaining the DNA sequence help in DMD dx?
Since we know the normal coding sequence, we can determine if the bp mutation will be missense, nonsense, etc
(this may not make sense once I leave class)
Mom has normal gene and offspring as a mutation. What is the likely cause?
germline mutation or de novo mutation (if there is a 2nd affected child, then you can say germ line mosaicism)
Why is it more ideal to test the infected person, rather than the normal offspring?
We know that the affected person has a detectable mutation, once the mutation is determined you can perform a direct genetic test on the proband (otherwise, a negative result testing the proband alone would be fairly inconclusive/could be a false negative)
After determining the mutation in an affected person, what test would you perform in related individuals?
Direct test
T/f: All mutations can be identified
F
In DMD pts they have little or no detectable ____ (a protein)
dystrophin
T or F: BMD have normal levels of dystrophin
F: they have lower than normal levels. The closer the levels are to normal, the less sever the phenotype is
What types of molecular defects are associated with DMD? (what proportions of pts Dx with DMD have this mutation)
2/3 large deletion in DMD exons
1/3 small insertions/deletions/point mutations
What is the mode of inheritence for DMD?
X-linked lethal
Will pts with BMD often have a frameshit mutation or a frame neutral deletion?
frame neutral = multiples of 3
T or F: there is extensive allelic heterogeneity in BRCA gene mutations
True
What is the mode of inheritance for BRCA assc familial breast cancer?
autosomal dominant
T or F: There is a limited allelic heterogeneity in BRCA mutations in the ashkenazi Jewish population. (Explain why this is True or False)
T: this corresponds to a “founder effect” (a common ancestor in the pop “brought” in a mutation and that was the one that got passes on)
What type of genetic test would be performed if you knew the chromosome/genomic marker that was involved in the phenotype?
linkage
If this is a bad question, feel free to throw it out. I don’t really like it.
What kind of genetic test can you perform if you know the gene that is contributing to the disease phenotype that is present?
direct
What type of genetic test is performed when there is extensive allelic heterogeneity assc with the disease phenotype?
scanning approach
What type of genetic testing is used to screen all or part of a gene to look for any sequence alteration?
scanning approach
How is germ line mosaicism “Dx”?
normal genotype in parent(s) with 2 abnormal children with the same mutation
When would we perform a genetic screening for a woman’s risk of BRCA assc familial breast cancer?
when she had a greater than 10% risk of having it (determined by algorithm)
What parts of the BRCA gene is screened?
promoter, exons, and splice junctions (intron and exon junction)
What are some of the limitations to genetic screening?
- mutations outside the scanned region are not detected
- polymorphisms may cause unequal allele amplification (false positive???)
Describe how sequence variants are interpreted.
- evidence based interp (look to data)
- 3 categories of results: variance is benign, deleterious, or unknown risk
- Its complicated
T or F: If a person gets a negative result from a genetic scanning test they have 0% risk of having a deleterious mutation
F: there are always risks that the test does not pick up
