A new test may help to streamline genetic testing for Huntington Disease (HD) by generating accurate results, avoiding unnecessary additional testing, and improving turnaround time.
The test, which uses chimeric or triplet repeat primed PCR (TP PCR) methodology, yielded results that were 100% concordant with standard genotyping methods in an analysis of 246 samples. The high sensitivity and specificity of the test could reduce the number of false negative results and facilitate both diagnosis and prognosis by correctly sizing the genetic abnormality characteristic of HD.
Huntington disease (also known as Huntington's disease or Huntington's chorea) is an inherited and progressive neurodegenerative disorder that typically becomes apparent during a person's thirties or forties. With time, HD patients develop diminished muscle coordination that is evident in walking, speaking, and swallowing and undergo changes in personality and thinking ability. A mutation in the Huntingtin gene leads to an abnormal number of repeats of a sequence of three nucleotides known as CAG. Based on the number of CAG repeats, a person may be deemed to be normal (10-35 repeats), at low risk (36-39 repeats), or at high risk (greater than 40 repeats) of having or developing HD symptoms. That is why accurately determining the number of CAG repeats is so important.
In this study, 246 samples that had been previously analyzed by other methods were tested with the new method (TP PCR). The samples included 14 DNA reference samples from the Coriell Cell Repositories, three samples from the College of American Pathologists 2002 Survey, and 229 samples from individuals tested at ARUP Laboratories for clinical purposes by standard technologies, explained lead investigator Elaine Lyon, PhD, Medical Director of Molecular Genetics, ARUP Laboratories and its Institute for Clinical and Experimental Pathology, and Department of Pathology, University of Utah, Salt Lake City, UT. Normal samples were included as well as those with a wide range of CAG repeats. The samples were blinded and analyzed.
The results showed that TP PCR correctly sized 240 of the 246 samples. All of the 100 samples in the normal and low risk groups were correctly sized. In the 146 samples of those known to be affected by HD (those with > 39 CAG repeats), the results for 140 correctly matched that found with other methods whereas the number of CAG repeats differed by ±1 in 6 samples, a difference said by the authors to be within the precision of the method at higher repeat numbers. Up to 101 CAG repeats could be accurately sized with this test. Even samples that were found to be challenging to analyze with other methods could be assessed solely and accurately by TP PCR.
Another advantage of this new method is its ability to identify true homozygous normal samples, thus avoiding further testing. With other methodologies, if a sample appears homozygous for the normal allele, additional testing, often with Southern blot analysis, is still recommended because of the risk of false negatives. "Southern blotting is expensive, labor intensive, requires high concentrations of DNA, and can delay turnaround time," says Dr. Lyon. However, when HD is suspected in children, Dr. Lyon and colleagues recommend that even with TP PCR, apparently homozygous samples should undergo further testing.
TP PCR uses a forward and reverse chimeric primer to amplify from multiple priming sites within the trinucleotide repeat. TP PCR produces a characteristic ladder on a fluorescence electropherogram that allows the rapid and inexpensive identification and quantification of expanded repeats. Major peaks and minor peaks (stutters) representing CAG repeats can be analyzed and sized automatically using commercially available software.
David Sampson | EurekAlert!
Laser activated gold pyramids could deliver drugs, DNA into cells without harm
24.03.2017 | Harvard John A. Paulson School of Engineering and Applied Sciences
What does congenital Zika syndrome look like?
24.03.2017 | University of California - San Diego
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy