The limitations of qPCR telomere length measurement in diagnosing dyskeratosis congenita.

Telomere length <1st percentile-for-age in leukocyte subsets by flow cytometry with fluorescence in situ hybridization (flow FISH) is highly sensitive and specific in diagnosing patients with dyskeratosis congenita (DC), a telomere biology disorder. We evaluated the clinical utility of the high-throughput quantitative real-time PCR (qPCR) relative telomere length (RTL) measurement as a diagnostic test for DC in patients with a priori clinical and/or genetic DC diagnoses. We calculated the sensitivity and specificity of RTL at different age-specific percentile cutoffs in 31 patients with DC and 51 mutation-negative relatives, and evaluated RTL difference by disease genotype. qPCR RTL <1st percentile-for-age failed to identify more than 60% of the patients already known to have DC (sensitivity = 39%, specificity = 98%). Three-quarters of DC patients had RTL below the 10th percentile-for-age (sensitivity = 74%), as did 12% of the unaffected relatives (specificity = 88%). Our findings suggest that the qPCR RTL method is not optimal for diagnosing DC. In light of these limitations, leukocyte flow FISH telomere length remains the recommended molecular test for diagnosing DC.