Single-Step Scalable-Throughput Molecular Screening for Huntington Disease

• Published in: Clinical chemistry (Baltimore, Md.) Md.), 2008-06, Vol.54 (6), p.964-972
• Main Authors: Teo, Clara R. L, Wang, Wen, Yang Law, Hai, Lee, Caroline G, Chong, Samuel S
• Format: Article
• Language: English
• Subjects: African Americans; Analytical, structural and metabolic biochemistry; Autoanalysis; Biological and medical sciences; Deoxyribonucleic acid; DNA; DNA - analysis; DNA polymerase; Electrophoresis, Capillary; Fluorescence; Fundamental and applied biological sciences. Psychology; Genetic testing; Genotype; Humans; Huntingtin Protein; Huntington Disease - genetics; Huntingtons disease; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Melting; Methods; Nerve Tissue Proteins - genetics; Nuclear Proteins - genetics; Polymerase Chain Reaction; Reference Values; Reproducibility of Results; Transition Temperature; Trinucleotide Repeat Expansion
• ISSN: 0009-9147; 1530-8561
• DOI: 10.1373/clinchem.2007.096503

Huntington disease (HD) is a fatal autosomal dominant neurodegenerative disorder caused by an unstable expansion of the CAG trinucleotide repeat in exon 1 of the HTT (huntingtin) gene and typically has an adult onset. Molecular diagnosis and screening for HD currently involve separate amplification and detection steps. We evaluated a novel, rapid microplate-based screening method for HD that combines the amplification and detection procedures in a single-step, closed-tube format. We carried out both the PCR for the HTT CAG-repeat region and the subsequent automated melting-curve analysis of the amplicon in the same wells on the plate. To establish cutoff melting temperatures (T(m)s) for each allelic class, we used a panel of reference DNA samples of known CAG-repeat sizes that represent a range of HTT alleles [normal (< or =26 repeats), intermediate (27-35 repeats), reduced penetrance expanded (36-39 repeats), and fully penetrant expanded (> or =40 repeats)]. We also measured well-to-well variation in T(m) across the thermal block and validated cutoff T(m)s with DNA samples from 5 different populations. We also conducted a blinded validation analysis of clinical samples from an additional 40 HD-affected and 30 unaffected individuals. We observed a strong correlation between CAG-repeat size and amplicon T(m) among the reference DNA samples. Use of the T(m) cutoffs we established revealed that 5 samples from unaffected individuals had been misclassified as affected (1.1% false-positive rate). All samples from HD-affected and unaffected individuals were correctly identified in the blinded analysis. This simple and scalable homogeneous assay may serve as a convenient, rapid, and accurate screen to detect the presence of pathologic expanded HD alleles in symptomatic patients.