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GENETIC FEATURES 

 

Huntingtin (HTT) gene is located in the short arme of chromosome 4 (4p16.3). This gene is linked to 8 dominantly inherited neurodegenerative diseases included Huntington disease (Deplow et al, 2012), which are known as polyglutamine diseases. The huntingtin misfolding due to the CAG expansion causes all these diseases. CAG repeats encodes glutamine.

 

CAG EXPANSION

The number of CAG repeats in HTT is associated with genetic anticipation. In the pathogenic range, repeat expansion inherited by progeny causes an earlier disease onset than the one observed in the parent. In the majority of cases this event occurs when a father passes the mutation to his offspring because of the repeat instability in spermatogenesis.

CAG repeat expansion accounts for 60 % of variance at age of onset. Environment and other genes also determine pathogenesis (Walker et al, 2007)

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Phenotypes according to number of CAG repeats in huntingtin gene

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