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BF - MM3

Human Mutation and Their Functional Effects

Is the dystrophin gene large/ small? Largest gene known
What % of the gene is comprised of introns? 99%
What are two diseases that result from mutations in the dystrophin gene? 1. Duchenne Muscular Dystrophy (DMD) 2. Becker Muscular Dystrophy (BMD)
What is the nature of the vast majority of mutations in DMD and BMD? Deletions of one or more whole exons
If whole exon deletion occurs in both DMD and BMD, what happens to cause differences in severity? 1. DMD = frameshift (deletion of non-multiple of 3 bases exon) 2. BMD = non-frameshift (Deletion of exon with multiple of 3 bases).
What happens to dystrophin protien in DMD in a) 85% of cases? b)15% of cases? a) Protein unrecognizable as dystrophin b) No protein due to premature stop codon
What happens to dystrophin protein in BMD? Truncated (shorter) dystrophin but semi-functional
For the requirements of translation. The stop codon must be: 1. On last... 2. Upstream of last... 3. Within... 1. On last exon 2. Upstream of last EJC 3. Within 50-55 nucleotide bases from last EJC
What is dystrophin? Cytoplasmic protein in muscle
What is the function of dystrophin? Anchors muscle cytoskeleton to extracellular matrix
Binding: ? <--> dystrophin <--> ? Glycoprotein, F-actin cytoskeleton
How are deletions in the dystrophin gene screened for? Analysis of PCR products in gel electrophoresis (look for missing exons)
What does osteogenesis imperfecta lead to (changes to bones)? (2) Increased none fragility and decreased bone mass
OI - Which two types are most common? Type I and IV
OI - What kind of inheritance pattern in seen in OI? Autosomal dominant
OI - What can be said about the origins of types II and III? Can also be sporadic
OI - What gene are point mutations in 90% of all cases seen in? ColA1/2
OI - What type of collagen does ColA1/2 code for? Type 1 collegen
OI - How can the structure of collagen be briefly described? Triple helix
OI - In type I collagen, what does the ColA1 gene code for? The two alpha-1 chains
OI - In type I collagen, what does the ColA2 gene code for? The one alpha-2 chain
OI - In type I collagen, what is found every 3rd residue that is needed fro correct intertwining of triple helix? Glycine
OI - In type I collagen, what is one of the most common point mutations? Glycine being substituted (often for valine)
OI - Cells with a glycine -> valine substitution in type 1 collagen produce...? A mixture of normal/ abnormal collagen
OI - What 3 things does the severity of OI depend on? Haplo-insufficiency of ColA1 gene, nature of point mutation, where mutation occurs in triple helix
OI - What could the two outcomes be of a point mutation in type 1 collagen? Substituting an amino acid (e.g. glycine) or premature stop codon
MILD OI - Major/ minor mutation? Major (premature stop codon)
MILD OI - What gene is damaged, if any? One ColA1 gene is damaged/ mutated
MILD OI - What chains are produced as a result of the damaged ColA1 gene? ONE alpha-1 chain and one alpha-2 chain
MILD OI - What is the % of normal/ damaged collagen? 50% normal, 50% damaged
MODERATE OI - What type of mutation Missense mutation
MODERATE OI - Result of mutation on alpha-1 and alpha-2 chains? alpha-1 is mutated and alpha-2 is produced normally
MODERATE OI - What is the % of normal/ damaged collagen? 25% normal, 75% damaged
MODERATE OI - The mutation is at the N-terminus of helix so...? Only minimal disturbances in packing
SEVERE OI - What type of mutation Missense mutation
SEVERE OI - Result of mutation on alpha-1 and alpha-2 chains? alpha-1 is mutated and alpha-2 is produced normally
SEVERE OI - What is the % of normal/ damaged collagen? 25% normal, 75% damaged
SEVERE OI - The mutation is at the C-terminus of helix so...? Major disturbances in packaging
Trinucleotide repeats - What are they? Simple sequence repeats that occur throughout the human genome and are normal and stable
Trinucleotide repeats - Give 3 examples of non-pathological TRs? Micro-satellites, telomers, centromers
Trinucleotide repeats - When can a mutation be pathogenic? When the mutation causes the number of repeats to lengthen to an unstable repeat number (e.g. trinucleotide repeat expansion diseases)
Trinucleotide repeats - Of the following repeats, which are non-coding disorders and which are coding disorder? a)CGG b)CAG c)GCC d)GAA e)CTG a)N-C b)C c)N-C d)N-C e)N-C
Trinucleotide repeats - Usually coding expandable repeats are CAG (glutamine). What pathology is caused? (3) Neuromuscular, neurodegenerative, mental retardation
Trinucleotide repeats - What gene is implicated in myotonic dystrophy DMPK
Trinucleotide repeats - What kind of gene is DMPK? Protein kinase gene
Trinucleotide repeats - What is myotonia? Failure of muscle to relax after contraction
Trinucleotide repeats - What is dystrophy? Muscle weakness
Trinucleotide repeats - In fragile x, how is the FMR gene silenced? By methylation
Trinucleotide repeats - What happens in Kennedy disease? Polyglutamate tracts accumulate in androgen receptor protien
Trinucleotide repeats - In Kennedy disease, what does loss of androgen receptors cause? (2) Neurodegeneration and androgen insensitivity -> testicular feminisation
Trinucleotide repeats - What happens in huntingtons disease? Polyglutamate tracts accumulate in Huntington protein
Trinucleotide repeats - Unlike normal Huntington protein, the mutated type aggregates where? In the nucleus
Trinucleotide repeats - The mutation confers a gain of function as the mutated Huntington aggregates are what? Cytotoxic
Trinucleotide repeats - 'Anticipation' The expansion grows through... leading to...? Successive generations...increasingly severe presentation
Trinucleotide repeats - Do spontaneous triplet expansions happen? Yes - but rare
Created by: benfenner1