Diagnostic utility of telomere length testing in a hospital-based setting

Abstract

Telomere length (TL) predicts the onset of cellular senescence in vitro but the diagnostic utility of TL measurement in clinical settings is not fully known. We tested the value of TL measurement by flow cytometry and FISH (flowFISH) in patients with mutations in telomerase and telomere maintenance genes. TL had a discrete and reproducible normal range with definable upper and lower boundaries. While TL above the 50th age-adjusted percentile had a 100% negative predictive value for clinically relevant mutations, the lower threshold in mutation carriers was age-dependent, and adult mutation carriers often overlapped with the lowest decile of controls. The extent of telomere shortening correlated with the age at diagnosis as well as the short telomere syndrome phenotype. Extremely short TL caused bone marrow failure and immunodeficiency in children and young adults, while milder defects manifested as pulmonary fibrosis-emphysema in adults. We prospectively examined whether TL altered treatment decisions for newly diagnosed idiopathic bone marrow failure patients and found abnormally short TL enriched for patients with mutations in some inherited bone marrow failure genes, such as RUNX1, in addition to telomerase and telomere maintenance genes. The result was actionable, altering the choice of treatment regimen and/or hematopoietic stem cell donor in one-fourth of the cases (9 of 38, 24%). We conclude that TL measurement by flowFISH, when used for targeted clinical indications and in limited settings, can influence treatment decisions in ways that improve outcome.

Keywords: aplastic anemia; interstitial lung disease; liver disease; precision medicine; primary immunodeficiency.

Fig. 1.

TL by flowFISH shows a reproducible normal range. (A) Nomogram of lymphocyte lengths from Johns Hopkins controls (n = 192) and controls from Vancouver (n = 444) with percentile lines as annotated. (B) Interlaboratory reproducibility of lymphocyte TL measurements from 18 samples, processed independently, shows outstanding concordance by linear regression.

Fig. 2.

TL has age-dependent diagnostic thresholds. (A and B) Lymphocyte TL measurements from 100 telomerase and telomere maintenance gene mutation carriers relative to the nomogram with the age-adjusted deviation from the median (ΔT) shown by two-decade intervals. In B, 1st and 10th percentile thresholds are annotated to the right. (C) Data from A separated by mutation carriers who had symptoms, defined as primary immunodeficiency, bone marrow failure, liver disease, or pulmonary fibrosis-emphysema, and those who had no symptoms. (D) The proportion of symptomatic patients increases with age, as indicated by the red circles and quantified in the proportions listed below each age group. (E) TL in lymphocytes annotated by mutant gene. (F) Shorter TL in DKC1 mutation carriers (males) relative to TERT and TR. Graphs in B, D, and E indicate means ± SEM, Mann–Whitney U test.

Fig. 3.

TL correlates with disease onset and disease type. (A) Dot plot shows age-dependent manifestations of the four common short telomere syndrome features. IPF-E refers to idiopathic pulmonary fibrosis with or without emphysema. BMF refers to bone marrow failure. PID refers to severe immunodeficiency, presenting usually in the setting of enterocolitis in infants. The P values to the right indicate difference in age relative to IPF-emphysema (Mann–Whitney U test). (B) Linear regression shows a correlation between deviation of lymphocyte TL from the age-adjusted median (ΔT) and the age at diagnosis of one of four short telomere syndrome features. The linear regression line and 95% confidence intervals are shown for the 73 symptomatic individuals from A. (C) The disease type correlates with ΔT with the percentile ranges, as shown below in the tabulated data. P values in C reflect ΔT comparisons relative to idiopathic pulmonary fibrosis-emphysema patients (Mann–Whitney U test).

Fig. 4.

Utility of TL in the diagnosis of idiopathic bone marrow failure. (A) Lymphocyte TL in 38 prospectively recruited patients with idiopathic aplastic anemia (AA) relative to controls. The red circles denote patients for whom a genetic diagnosis was identified with documentation of a mutation in a telomere maintenance gene (TERT n = 4, TR n = 1, RTEL1 n = 1, DKC1 n = 1, TINF2 n = 1) or nontelomere gene (GATA2 n = 2, RUNX1 n = 1, LIG4 n = 1). The latter group is denoted by an asterisk (*). The blue circles denote patients treated with immunosuppression who responded (all the treated patients responded). The remaining cases, denoted by black and gray circles, denote cases of constitutional aplastic anemia and untreated cases, respectively. Larger circles indicate the 22 patients who reached an informative endpoint (either a genetic diagnosis made or treatment with immunosuppression). (B) The degree of deviation from the age-adjusted median (ΔT) from three groups is shown: prospectively recruited patients who had a response to immunosuppression at 1 y (n = 10, 5 complete response, 5 partial response), patients with telomerase and telomere gene mutations identified in A (TERT, TR, RTEL1, DKC1, TINF2, n = 8), as well as 11 patients successfully treated with immunosuppression who were in remission for 2 y or more. Means ± SEM are shown, Mann–Whitney U test. The 1st, 10th, and 90th percentiles are annotated to the right in B.