Abstract
BackgroundMachado-Joseph disease (MJD), caused by a CAG repeat expansion located in exon10 of the ATXN3 gene, is now regarded as one of the most common spinocerebellar ataxia (SCA) in the world. The relative frequency of MJD among SCA has previously been estimated at about 50% in the Chinese population and has been reported to be related to the frequency of large normal alleles in some populations. Taq polymerase has been used for PCR in nearly all studies reported previously.MethodsNormal and expanded alleles of ATXN3 were detected via PCR using LA Taq DNA polymerase (better for GC-rich sequences) and denaturing polyacrylamide gel electrophoresis in 150 normal individuals and 138 unrelated probands from autosomal dominant SCA families. To compare reaction efficiency, 12 MJD patients' expanded alleles were amplified with La Taq and Taq polymerase respectively in the same amplifying systems and reaction conditions.ResultsNormal alleles ranged from 12 to 42 CAG repeats. The most common allele contained 14 repeats with a frequency of 23.3%, which corroborates previous reports. The frequency of large normal alleles (>27 repeats) was 0.28, which was very high relative to previous reports. The frequency of MJD in SCA patients was 72.5%, which was significantly higher than those in previous reports about the Chinese and other Asian populations. This frequency was one of the highest reported worldwide, with only Portuguese and Brazilian populations exhibiting higher proportions. All 12 expanded alleles were amplified in PCR with La Taq polymerase, whereas only 2 expanded alleles were amplified with Taq polymerase.ConclusionWe have first reported the highest relative frequency of MJD in Asia, and we attribute this high frequency to a more efficient PCR using LA Taq polymerase and hypothesized that large ANs may act as a reservoir for expanded alleles in the Southeastern Chinese population.
Highlights
Machado-Joseph disease (MJD), caused by a CAG repeat expansion located in exon10 of the ATXN3 gene, is regarded as one of the most common spinocerebellar ataxia (SCA) in the world
We have recruited 150 unrelated healthy individuals and 138 probands from autosomal dominant SCA families of Southeastern Chinese origin to analyze the distributions and characteristics of CAG repeats of ATXN3, and have found a much higher frequency (72.5%) of MJD in SCA patients compared to previous reports. This relative frequency is only slightly less than that reported in the Portuguese and Brazilian populations (84.2%) [16,17]. We have attributed this high relative frequency to better detection of expanded alleles via more efficient PCR using LA Taq polymerase and hypothesized that large ANs may act as a reservoir for expanded alleles in the Southeastern Chinese population
The difference in the frequency of large ANs between the present study and other studies involving Japanese [9], Indian [10], Czech [11] populations and a combined population comprised of Acadian, Black, Caucasian, Inuit and Thai [21] is shown in table 1
Summary
Machado-Joseph disease (MJD), caused by a CAG repeat expansion located in exon of the ATXN3 gene, is regarded as one of the most common spinocerebellar ataxia (SCA) in the world. Taq polymerase has been used for PCR in most studies reported previously. Amplifying systems and ion conditions vary across studies, Taq polymerase was used for PCR in most previous reports. The efficiency of amplification is affected by long length and high GC content in the amplified sequence when using Taq polymerase [6] and it is difficult to amplify expanded alleles having large CAG repeats [7]. Here we use the LA Taq polymerase which is better for amplifying expanded alleles with GCrich sequences
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