Expansions and Huntington's Disease

by Georgina Cornwall, PhD

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    In our final lecture on single gene inheritance, we’ll be looking at expansions and mitochondrial inheritance. Now, what are expansions? I brought them up very briefly in an earlier lecture. Trinucleotide repeat expansions are what we’re talking about. If you don’t recall anything about expansions previously, you can probably get from the title trinucleotide, three nucleotides and repeat, they keep repeating and they keep expanding. These are dynamic mutations. They change from generation to generation. As it’s passed down from one parent to their offspring, the number of repeats almost generally will increase. We don’t really notice it when it’s decreasing. They are expanding repeats. The repeats are normal in the population, regular number. At a certain number, they become abnormal and result in some phenotypic problems. Again, they’re expanding as they go from generation to generation. You can recall very easily from the title exactly what’s going on because they’re named appropriately. There are two main diseases that we’ll be considering: Huntington’s disease which is a polyglutamine disease, meaning we get many more glutamine residues in a particular gene than we would like to have. Then Fragile X, I brought that up when we were talking about X-linked disorders because indeed, it is an X-linked disorder. Let’s take a look first at Huntington’s disease, a polyglutamine disease. It’s an expanding repeat. It’s an expanding repeat of C, A, and G, so CAG, CAG, CAG. It’s normal to have about 25 repeats of this in the Huntington gene which is on chromosome 4. It’s not a sex-linked disease. This is an autosomally inherited disease. The CAG from uneven crossing over or from maybe translocations but either way, the CAG repeat, replication causes these extra repeats. Once an individual has more than 40 repeats, we see expression of Huntington’s disease. What...

    About the Lecture

    The lecture Expansions and Huntington's Disease by Georgina Cornwall, PhD is from the course Single-Gene Disorders. It contains the following chapters:

    • Expansions and Mitochondrial Inheritance
    • Polyglutamine Disease - Huntingston's

    Author of lecture Expansions and Huntington's Disease

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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