Comparison Between Agarose Gel Electrophoresis and Automated Capillary Electrophoresis in the Detection of CAG Replications in Gene HTT

Abstract

Huntington´s disease is a rare genetic, neurodegenerative, progressive and fatal illness, with dominant autosomic inheritance. It is caused by the number of abnormal CAG replications in exon 1 of the gene HTT in 4p16.3. The molecular test is highly important to confirm HD´s clinic diagnosis. Molecular testing involves the amplification of the region by PCR technique and later analysis of the fragments generated (amplicons). Current research compares two techniques for the analysis of amplicons: agarose gel electrophoresis (2.5%) and automated capillary electrophoresis in the determination of the number of CAG repetition units of the gene HTT. Results of agarose gel electrophoresis show that a negative co-relationship exists between the initial age and CAG replications (r = -0.63; p<0.05). However, results of capillary electrophoresis show a stronger negative co-relationship between HD initial age and the number of CAG replications (r = -0.89; p<0.0001). Variation in CAG repetitions between techniques lie between -23 and +48 CAG repetitions. Twenty out of the 26 individuals investigated had the same diagnosis regardless of the technique employed and six had a different diagnosis according to the technique employed. Sensitiveness of agarose gel electrophoresis was 83% when compared to capillary electrophoresis and specificity reached 62.5%. Results show that agarose gel electrophoresis overestimates the number of CAG replications of the gene HTT, as a low precision test for HD diagnosis.