Which two of these diseases are caused by a triplet repeat expansion?
Other human diseases in which triplet repeat expansion occurs are fragile X syndrome, several spinocerebellar ataxias, myotonic dystrophy and Friedreich’s ataxia.
What are two examples of triplet repeat mutations and what disease are they each associated with how do they cause disease?
However, the more common triplet repeat disorders are autosomal dominant. Some examples of conditions caused by triplet repeat expansions are fragile X syndrome, myotonic muscular dystrophy, and Huntington disease.
What diseases are caused by trinucleotide repeats?
At least seven disorders result from trinucleotide repeat expansion: X-linked spinal and bulbar muscular atrophy (SBMA), two fragile X syndromes of mental retardation (FRAXA and FRAXE), myotonic dystrophy, Huntington’s disease, spinocerebellar ataxia type 1 (SCA1), and dentatorubral-pallidoluysian atrophy (DRPLA).
What is triplet repeat disorders?
Trinucleotide repeat disorders, also known as microsatellite expansion diseases, are a set of over 50 genetic disorders caused by trinucleotide repeat expansion, a kind of mutation in which repeats of three nucleotides (trinucleotide repeats) increase in copy numbers until they cross a threshold above which they become …
What is repeat expansion disorders?
Repeat expansion disorders are a class of genetic diseases that are caused by expansions in DNA repeats. The DNA repeats come in various sizes from single nucleotides to dodecamers or longer. The threshold at which the repeat expansions become symptomatic varies with the specific disease.
What causes repeat expansion?
Repeat expansion diseases include both causes of myotonic dystrophy (DM1 and DM2), the most common genetic cause of amyotrophic lateral sclerosis/frontotemporal dementia (C9ORF72), Huntington disease and eight other polyglutamine disorders including the most common forms of dominantly inherited ataxia, the most common …
How is the trinucleotide repeat expansion a factor in the disease?
Instability of repetitive DNA sequences within the genome is associated with a number of human diseases. The expansion of trinucleotide repeats is recognized as a major cause of neurological and neuromuscular diseases, and progress in understanding the mutations over the last 20 years has been substantial.
How are trinucleotide repeats diagnosed?
Testing for FXS and similar trinucleotide repeat disorders (e.g., myotonic dystrophy, Huntington disease, spinocerebellar ataxias, spinal and bulbar muscular atrophy, and Friedreich ataxia) is typically performed using Southern blot (5) or, more recently, by PCR and capillary electrophoresis (6, 7).
Does the number of repeats matter in regards to your risk of getting HD?
Individuals with six to 35 CAG repeats will be unaffected; individuals with 36-39 repeats will be at increased risk for HD; and individuals with 40 or more CAG repeats will definitely manifest disease phenotypes (MacDonald et al., 1993; Bates, 2005).
How do you test for trinucleotide repeat disorders?
Why are long CAG repeats unstable?
CAG repeats on HD chromosomes were unstable when transmitted from parent to offspring. Instability appeared more frequent and stronger upon transmission from a male than from a female, with a clear tendency towards increased size.
Which is the first triplet disease to be identified?
Trinucleotide repeat disorder. The first triplet disease to be identified was fragile X syndrome, which has since been mapped to the long arm of the X chromosome. At this point, there are from 230 to 4000 CGG repeats in the gene that causes fragile X syndrome in these patients, as compared with 60 to 230 repeats in carriers…
How are trinucleotide repeat disorders related to age?
Trinucleotide repeat expansion. In 2007, a new disease model was produced to explain the progression of Huntington’s Disease and similar trinucleotide repeat disorders, which, in simulations, seems to accurately predict age of onset and the way the disease will progress in an individual, based on the number of repeats of a genetic mutation.
Why are trinucleotide repeat disorders called Microsatellite expansion?
Trinucleotide repeat disorders, also known as microsatellite expansion diseases, are a set of over 50 genetic disorders caused by trinucleotide repeat expansion, a kind of mutation in which repeats of three nucleotides (trinucleotide repeats) increase in copy numbers until they cross a threshold above which they become unstable.
What causes reduced penetrance in human inherited disease?
Reduced penetrance in some genetic disorders may also depend on genetic background of gene carriers. In Hirschsprung disease (HSCR), although the presence of RET mutations is sufficient to explain HSCR inheritance, a genome scan reveals that new susceptibility locus on 9q-31 is also required to cause the disease [20].
What causes the expansion of triplet repeat DNA?
Genetic diseases, such as Fragile-X syndrome, have been linked to the expansion of trinucleotide repeat (a.k.a. triplet repeat) DNA sequences ofthe 5′-(CNG)n-3′ motif during replication This expansion is related to the formation ofself-complementary hairpins that cause reiterative DNA synthesis.
Trinucleotide repeat disorder. The first triplet disease to be identified was fragile X syndrome, which has since been mapped to the long arm of the X chromosome. At this point, there are from 230 to 4000 CGG repeats in the gene that causes fragile X syndrome in these patients, as compared with 60 to 230 repeats in carriers…
Trinucleotide repeat expansion. In 2007, a new disease model was produced to explain the progression of Huntington’s Disease and similar trinucleotide repeat disorders, which, in simulations, seems to accurately predict age of onset and the way the disease will progress in an individual, based on the number of repeats of a genetic mutation.
Trinucleotide repeat disorders, also known as microsatellite expansion diseases, are a set of over 50 genetic disorders caused by trinucleotide repeat expansion, a kind of mutation in which repeats of three nucleotides (trinucleotide repeats) increase in copy numbers until they cross a threshold above which they become unstable.