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MOLECULAR GENETIC TESTING

This test is based on targeted mutation analysis. The Huntington gene is the only gene associated with HD. Molecular testing of huntingtin gene could be performed in order to determine the number of CAG repeats and to prediagnose patients bearing CAG expansion. (Potter et al, 2004)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A PCR should be performed to detect alleles until 115 CAG repeats. It must be considered polymorphic CAG repeat adjacent sequences such as CCG repeat lying 3’ CAG repeat. This polymorphic sequence might modify primer-annealing sites or loss of interruption between CAG and CCG tracts and this can results in misinterpretation of genotyping data because of the misalignment of primers and the miscalculation of uninterrupted CAG repeat length. (Potter et al, 2004)

 

A Southern blot should be performed to identify large expansions associated with Juvenile-onset HD and to confirm homozygous normal. The mutation detection frequency of this test method is 100 %. This test should be performed in case of:

 

  • Confirmatory testing: Establishing diagnosis in a proband

 

  • Predictive testing: it is not offered for minors. This test is performed to determine the carrier status

 

  • Prenatal testing in amniotic fluid cells and chorionic villus samples: it should be carried out in case of high risk pregnancies.

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