A Study of Triplet-Primed PCR for Identification of CAG Repeat Expansion in the HTT Gene in a Cohort of 503 Indian Cases with Huntington’s Disease Symptoms
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Huntington’s disease (HD) is an autosomal-dominant neurodegenerative disorder with an average age at onset of 40 years. It is a polyglutamine (polyQ) disorder that is caused by an increase in the number of CAG repeats in the huntingtin (HTT) gene. Genetic tests that accurately determine the number of CAG repeats are performed for confirmation of diagnosis, predictive testing of persons at genetic risk for inheriting HD, and prenatal testing. The aim of our study was to evaluate efficacy of triplet-primed polymerase chain reaction (TP-PCR) for routine diagnosis of HD in suspected cases from India.
We evaluated a combination of CAG flanking PCR and triplet-primed PCR for estimation of CAG repeats in 503 cases with clinical suspicion of HD.
There were 250 cases (49.7%) that showed the presence of expanded alleles, with 241 (47.9%) being fully penetrant alleles and nine (1.8%) in the reduced penetrance category. There were seven juvenile cases with an age of onset of < 20 years, with the longest allele comprising 106 CAG repeats found in an 8-year-old male patient. The results demonstrated an inverse (R = − 0.67) relationship between CAG length and age at clinical onset.
Our study on pan-Indian cases is one of the largest studies reported so far in India and focuses on the most accurate and comprehensive molecular diagnostic evaluation of HD.
Compliance with Ethical Standards
Conflict of interest
All the authors were employed by Metropolis Healthcare Ltd. PC, MC, YS, TD, AP, SP, RB and NS have no conflicts of interest to disclose.
No funding supported this study.
Ethics approval and consent to participate
The study procedures were approved by Conscience Independent Ethics Committee (CIEC). Informed consent was obtained from all participating individuals.
- 2.Moily NS, Kota LN, Anjanappa RM, Venugopal S, Vaidyanathan R, Pal P, et al. Trinucleotide repeats and haplotypes at the huntingtin locus in an Indian sample overlaps with European haplogroup a. PLoS Curr. 2014. https://doi.org/10.1371/currents.hd.a3ad1a381ab1eed117675145318c9a80.PubMedPubMedCentralGoogle Scholar
- 15.Bates G, Tabrizi S, Jones L. Huntington’s disease. 4th ed. Oxford: Oxford University Press; 2014.Google Scholar
- 19.Losekoot M, van Belzen MJ, Seneca S, Bauer P, Stenhouse SA, Barton DE. European Molecular Genetic Quality Network (EMQN). EMQN/CMGS best practice guidelines for the molecular genetic testing of Huntington disease. Eur J Hum Genet. 2013;21:480–6. https://doi.org/10.1038/ejhg.2012.200.CrossRefPubMedGoogle Scholar
- 21.Kay C, Collins JA, Miedzybrodzka Z, Madore SJ, Gordon ES, Gerry N, et al. Huntington disease reduced penetrance alleles occur at high frequency in the general population. Neurology. 2016;87:282–8. https://doi.org/10.1212/WNL.0000000000002858 Epub 2016 Jun 22.CrossRefPubMedPubMedCentralGoogle Scholar
- 22.Sequeiros J, Ramos EM, Cerqueira J, Costa MC, Sousa A, Pinto-Basto J, Alonso I, et al. Large normal and reduced penetrance alleles in Huntington disease: instability in families and frequency at the laboratory, at the clinic and in the population. Clin Genet. 2010;78:381–7. https://doi.org/10.1111/j.1399-0004.2010.01388.x.CrossRefPubMedGoogle Scholar