Gene Scanning Flashcards
What is Duchenne muscular dystrophy?
fatal x-linked recessive disease. progressive weakness and muscle loss. Dystrophin, functions in cytoskeletal structure of striated muscle cells.
What is Becker muscular dystrophy?
caused by mutations in the same gene as DMD but has milder phenotype.
Which patient would you except to have more dystrophin: those with DMD or those with BMD?
those with BMD have more dystrophin, though some of it may be abnormal. It is less severe than DMD.
What is special about the DMD gene?
largest known gene in the human genome (2.2 Mb). It has a high mutation rate (1/3 of affected males are new mutations).
Are mutations in DMD gene usually small?
No. Over 2/3 of mutations in DMD gene are large deletions that span one or more exons.
Less than 1/3 are small insertions/deletions.
Is DMD or BMD more likely to occur if there is a frameshift mutation in the gene?
DMD is more likely because frameshift will cause huge sections of errors and be a very severe mutation.
Describe the BRCA1 gene.
tumor suppresssor gene on chromosome 17
autosomal dominant transmission
protein has role in genomic stability.
When is it best to use gene scanning?
when you suspect a disorder that has extensive allelic heterogeneity where familes have unique ‘private’ mutations or the disease has a high rate of new mutations.
What is mode of inheritance for cystic fibrosis?
autosomal recessive. most mutations are inherited from carriers. Mosaicism very uncommon
What is mode of inheritance for Duchenne muscular dystrophy?
x-linked recessive. Most mutations are new. mosaicism is common.
What are the disadvantages of gene scanning?
results are complicated and difficult to interpret. Requires a body of previous knowledge and data to compare results to.
What are the advantages of gene scanning?
useful when there is extensive allelic heterogeneity. Not specific enough to pick up small deletions.
What would you look for in a diagnostic biopsy of muscle tissue for DMD?
absence of dystrophin protein
When presented with an affected patient who has a family history, who is the best person to test first?
the affected patient who came in
