Here we discuss the key findings and conclusions from a recently published study ‘Comparison of flow FISH and MM-qPCR telomere length assessment techniques for the screening of telomeropathies’.

Why test telomere length, and how?

Telomere length testing is an important element in the diagnosis of dyskeratosis congenita (DC) and telomere biology disorders (TBDs) when assessing bone marrow failure (BMF) syndromes. Correct diagnosis is critical to enable accurate care management, suitable treatment choices and optimal outcomes.

“Clinically, a correct telomere length assessment is of utmost importance for affected patients and their families and has immediate clinical consequences.” Ferreira et al. (2019)

There are a range of different methods available for telomere length testing. This study directly compared two of these; fluorescence in situ hybridization (Flow FISH) and monochrome multiplex-quantitative polymerase chain reaction (MM-qPCR).

Blood samples from 105 patients, with suspected DC or telomeropathy (telomere biology disorder), from Germany, Austria and Switzerland, were analyzed. Samples were tested using both Flow FISH and MM-qPCR. If the telomeres were found to be critically short, the samples also underwent next-generation sequencing (NGS). They were tested for 10 of the 15 known TBD causing genes.

Which telomere testing method should be used for clinical diagnostics, and why?

Based on analysis from 16 cases with a confirmed DC genetic cause, identified by NGS, the study concludes that Flow FISH is the better choice for clinical screening of suspected DC in adults with BMF. This is for a number of reasons:

1. Sensitivity:

   The study found that the sensitivity of both methods was high, with no significant difference between them, but with higher performance for Flow FISH (telomere length ≤1^st percentile sensitivity of Flow FISH and MM-qPCR was 75% and 69% respectively; i.e. the percentage of correctly diagnosed people)

2. Specificity:

   The specificity of Flow FISH was consistently higher than MM-qPCR for all thresholds tested. This difference was statistically significant between the 1^st and the 10^th percentiles. This reflects the finding that more patients without DC were correctly identified as such by Flow FISH in this measurement range. High specificity is particularly important when testing older adults

3. False positives:

   The rate of false positive results was higher when testing with MM-qPCR compared to Flow FISH. At the 10^th percentile this was a significant difference (60% for MM-qPCR vs. 35% for Flow FISH, p=0.03)

Another benefit of Flow FISH noted in the paper is the ability to measure the telomere length of granulocytes and lymphocytes separately, using the same blood sample.

Within the study, the researchers were able to compare results from these two Flow FISH cell subsets with MM-qPCR, both separately and combined. To note, the results listed above are from the lymphocyte Flow FISH testing.

Published in the Annals of the New York Academy of Sciences, the findings have been welcomed by the Telomere Biology Disorder (TBD) community as additional guidance to support screening and diagnosis of TBDs.

To find out more, read our blog on Dyskeratosis Congenita, Telomere Biology Disorders and the role of telomere length testing.

For further information on the Flow FISH process at RepeatDx, read our blog what is Flow FISH telomere testing?

Sources

Ferreira, M. S., Kirschner, M. Halfmeyer,I. et al. Comparison of flow‐FISH and MM–qPCR telomere length assessment techniques for the screening of telomeropathies. Annals of the New York Academy of Sciences. 2019. doi:10.1111/nyas.14248.