Human Mutation and Their Functional Effects
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| Is the dystrophin gene large/ small? | Largest gene known
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| What % of the gene is comprised of introns? | 99%
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| What are two diseases that result from mutations in the dystrophin gene? | 1. Duchenne Muscular Dystrophy (DMD)
2. Becker Muscular Dystrophy (BMD)
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| What is the nature of the vast majority of mutations in DMD and BMD? | Deletions of one or more whole exons
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| 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).
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| 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
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| What happens to dystrophin protein in BMD? | Truncated (shorter) dystrophin but semi-functional
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| 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
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| What is dystrophin? | Cytoplasmic protein in muscle
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| What is the function of dystrophin? | Anchors muscle cytoskeleton to extracellular matrix
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| Binding: ? <--> dystrophin <--> ? | Glycoprotein, F-actin cytoskeleton
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| How are deletions in the dystrophin gene screened for? | Analysis of PCR products in gel electrophoresis (look for missing exons)
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| What does osteogenesis imperfecta lead to (changes to bones)? (2) | Increased none fragility and decreased bone mass
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| OI - Which two types are most common? | Type I and IV
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| OI - What kind of inheritance pattern in seen in OI? | Autosomal dominant
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| OI - What can be said about the origins of types II and III? | Can also be sporadic
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| OI - What gene are point mutations in 90% of all cases seen in? | ColA1/2
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| OI - What type of collagen does ColA1/2 code for? | Type 1 collegen
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| OI - How can the structure of collagen be briefly described? | Triple helix
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| OI - In type I collagen, what does the ColA1 gene code for? | The two alpha-1 chains
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| OI - In type I collagen, what does the ColA2 gene code for? | The one alpha-2 chain
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| OI - In type I collagen, what is found every 3rd residue that is needed fro correct intertwining of triple helix? | Glycine
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| OI - In type I collagen, what is one of the most common point mutations? | Glycine being substituted (often for valine)
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| OI - Cells with a glycine -> valine substitution in type 1 collagen produce...? | A mixture of normal/ abnormal collagen
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| 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
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| 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
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| MILD OI - Major/ minor mutation? | Major (premature stop codon)
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| MILD OI - What gene is damaged, if any? | One ColA1 gene is damaged/ mutated
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| MILD OI - What chains are produced as a result of the damaged ColA1 gene? | ONE alpha-1 chain and one alpha-2 chain
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| MILD OI - What is the % of normal/ damaged collagen? | 50% normal, 50% damaged
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| MODERATE OI - What type of mutation | Missense mutation
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| MODERATE OI - Result of mutation on alpha-1 and alpha-2 chains? | alpha-1 is mutated and alpha-2 is produced normally
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| MODERATE OI - What is the % of normal/ damaged collagen? | 25% normal, 75% damaged
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| MODERATE OI - The mutation is at the N-terminus of helix so...? | Only minimal disturbances in packing
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| SEVERE OI - What type of mutation | Missense mutation
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| SEVERE OI - Result of mutation on alpha-1 and alpha-2 chains? | alpha-1 is mutated and alpha-2 is produced normally
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| SEVERE OI - What is the % of normal/ damaged collagen? | 25% normal, 75% damaged
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| SEVERE OI - The mutation is at the C-terminus of helix so...? | Major disturbances in packaging
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| Trinucleotide repeats - What are they? | Simple sequence repeats that occur throughout the human genome and are normal and stable
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| Trinucleotide repeats - Give 3 examples of non-pathological TRs? | Micro-satellites, telomers, centromers
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| 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)
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| 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
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| Trinucleotide repeats - Usually coding expandable repeats are CAG (glutamine). What pathology is caused? (3) | Neuromuscular, neurodegenerative, mental retardation
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| Trinucleotide repeats - What gene is implicated in myotonic dystrophy | DMPK
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| Trinucleotide repeats - What kind of gene is DMPK? | Protein kinase gene
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| Trinucleotide repeats - What is myotonia? | Failure of muscle to relax after contraction
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| Trinucleotide repeats - What is dystrophy? | Muscle weakness
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| Trinucleotide repeats - In fragile x, how is the FMR gene silenced? | By methylation
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| Trinucleotide repeats - What happens in Kennedy disease? | Polyglutamate tracts accumulate in androgen receptor protien
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| Trinucleotide repeats - In Kennedy disease, what does loss of androgen receptors cause? (2) | Neurodegeneration and androgen insensitivity -> testicular feminisation
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| Trinucleotide repeats - What happens in huntingtons disease? | Polyglutamate tracts accumulate in Huntington protein
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| Trinucleotide repeats - Unlike normal Huntington protein, the mutated type aggregates where? | In the nucleus
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| Trinucleotide repeats - The mutation confers a gain of function as the mutated Huntington aggregates are what? | Cytotoxic
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| Trinucleotide repeats - 'Anticipation' The expansion grows through... leading to...? | Successive generations...increasingly severe presentation
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| Trinucleotide repeats - Do spontaneous triplet expansions happen? | Yes - but rare
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