Trinucleotide repeat sequence defect is not seen in
Correct Answer: Alzhiemer's disease
Description: (B) Alzhiemer's disease # Alzheimer's disease (AD), also known simply as Alzheimer's, is a neurodegenerative disease that, in its most common form, is found in people over age 65. Approximately 24 million people worldwide have dementia of which the majority (-60%) is due to Alzheimer's.> The ultimate cause of Alzheimer's is unknown.> Genetic factors are clearly indicated as evidenced by dominant mutations in three different genes have been identified that account for the small number of cases of familial, early-onset AD.> For the more common form of late onset AD (LOAD), ApoE is the only clearly established susceptibility gene. All four genes can contain mutations or variants that confer increased risk for AD, but account for only 30% of the genetic picture of AD.> These four genes have in common the fact that mutations in each lead to the excessive accumulation in the brain of Ab, the main component of the senile plaques that litter the brains of AD patients> Huntington disease is caused by a defect in the gene (an inherited unit which contains a code for a protein) of unknown function called Huntington. The nucleotide codes (building blocks of genes arranged in a specific code which chemically forms into proteins), contain CAG repeats (40 or more of these repeat sequences).> The extra building blocks in the Huntington gene cause the protein that is made from it to contain an extra section as well. It is currently thought that this extra protein section, or portion, interacts with other proteins in brain cells where it occurs, and that this interaction ultimately leads to cell death.> The HD gene is a dominant gene, meaning that only one copy of it is needed to develop the disease. HD affects both males and females. The gene may be inherited from either parent, who will also be affected by the disease. A parent with the HD gene has a 50% chance of passing it on to each offspring. The chances of passing on the HD gene are not affected by the results of previous pregnancies.# Trinucleo Repeat Syndrome: Category I: Huntington disease and spinocerebellar ataxia Category II: Phenotypically diseases with expansions which all heterogenous small in magnitude but also found in exons of genes Category III: Fragile X syndrome, myotonic dystrophy, two of spirocerebellar ataxias, Juvenile myoclonic epilepsy, friedrich's ataxia. Have typically larger repeat expansions, located outside protein coding regions of genes.> Spinocerebellar ataxia type 2 is a minor cause of familial parkinsonism.
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