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Published on: December 10, 2021
Discrepancies in reporting the CAG repeat lengths for Huntington's disease
Oliver W Quarrell1, Olivia Handley, Kirsty O'Donovan
1Department of Clinical Genetics, Sheffield Children's Hospital, Sheffield, UK. Oliver.quarrell@sch.nhs.uk
European Journal of Human Genetics : EJHG
|August 4, 2011
Summary
Huntington's disease diagnostic testing shows significant CAG repeat length discrepancies between labs. Applying European and American guidelines greatly reduces errors, highlighting the need for standardized reporting and quality control in genetic testing.
Area of Science:
- Genetics
- Molecular Biology
- Neurology
Background:
- Huntington's disease is caused by CAG repeat expansion in the Huntingtin gene.
- Accurate CAG repeat length measurement is crucial for diagnosis and patient management.
- Variability in laboratory testing can impact diagnostic accuracy.
Purpose of the Study:
- To assess the accuracy and consistency of CAG repeat length measurements in Huntington's disease diagnostics.
- To compare results from routine diagnostic laboratories with central reference testing.
- To evaluate the impact of proposed error margins on reported discrepancies.
Main Methods:
- Comparison of 1326 duplicate CAG repeat length results from 121 laboratories across 15 countries.
- Analysis of upper and lower allele discrepancies.
- Re-analysis of 348 samples by an accredited German laboratory.
- Evaluation against American College of Medical Genetics and European Best Practice Guidelines.
Main Results:
- 51% discrepancy in upper allele reporting, reduced to 13.3% and 9.7% with guideline application.
- 40% discrepancy in lower allele reporting.
- Clinically significant discrepancies in 4.0% of cases, with a 0.3% potential misdiagnosis rate.
- High concordance (93-100%) when accredited labs applied error margins.
Conclusions:
- Significant inter-laboratory variability exists in Huntington's disease genetic testing.
- Adherence to standardized error margins is essential for improving diagnostic accuracy.
- Laboratories should report measurement error rates, participate in EQA, and use reference materials.
