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Letters to the Editor
FANCG (n=3), RPL5 (n=2), RPS19 (n=1), RPS17 (n=1), SBDS (n=1), and BLM (n=1). Homozygous mutations were found in three patients (2 in FANCG and 1 in FANCA), compound heterozygous mutations in four patients (2 in FANCA and 1 each in FANCG and SBDS), hemizygous mutations in three patients in FANCA, and heterozygous mutations in 14 patients (6 in TINF2, 3 in TERT, 2 in RPL5, and 1 each in RPS17, RPS19, and BLM). Each patient’s genetic variants are shown in Online Supplementary Table S2.
Out of the 133 patients and following the diagnostic flowchart (Figure 1A), 11 were diagnosed with DC (8%), 15 with non-DC IBMFS (11%), and 107 with AA (81%). The schematic representation of the results of gene analysis and the clinical features of IBMFS are shown in Figure 1B. Of the 11 patients with DC, nine were genet- ically diagnosed (6 with mutations in TINF2 and 3 with mutations in TERT), and those without diagnostic genetic mutations were diagnosed on the basis of clinical criteria. The 15 non-DC IBMFS cases consisted of nine FA, four DBA, one SDS, and one Bloom syndrome. All of these diagnoses were confirmed by the presence of germline mutations in IBMFS-related genes. Physical anomalies were observed in 11 of 15 (73%) patients. The individual clinical features and genetic results of the patients with IBMFS are shown in Online Supplementary Table S2.
We compared the clinical characteristics of patients with DC, non-DC IBMFS, and AA (Table 1). The median age and gender distribution did not show significant dif- ferences among the three groups. Severe or very severe cytopenia was significantly more frequent (P=0.024) in AA cases (57/107, 53%) than in DC (3/10, 30%) and non-DC IBMFS cases (2/12, 17%).
The median TL in patients with DC, non-DC IBMFS, and AA were −3.50 SD (range, −5.73 to +0.83 SD), −1.89 SD (range, −4.74 to +2.05 SD), and −0.84 SD (range, −4.27 to +4.00 SD), respectively (Figure 2A). Patients with DC had significantly shorter TL compared to those with non-DC IBMFS (P=0.031) and AA (P<0.001). Furthermore, patients with non-DC IBMFS tended to have shorter TL than those with AA (P=0.096).
To validate the efficacy of TL measurement in diagnos- ing DC and IBMFS, receiver operating characteristic curves identified two cut-off values with the optimum sensitivity and false positive rate (1-specificity) combina- tion, <−2.19 SD (for patients with DC) (Figure 2B) and <−1.71 SD (for patients with IBMFS) (Figure 2C), defined as “very short TL” and “relatively short TL,” respectively. For the diagnosis of patients with IBMFS, the TL cut-off value at −1.71 SD (relatively short TL) yielded a relatively high negative predictive value (0.921; 95% confidence interval [95% CI]: 0.873-0.958) and a moderately positive predictive value (0.432; 95% CI: 0.333-0.505). Of the total cohort, 44 patients (33%) were classified as having “relatively short TL”, which was significantly more fre- quent (P<0.001) in DC (10/11, 91%) and non-DC IBMFS (9/15, 60%) than in AA (25/107, 23%).
Although germline mutations in TL maintenance genes are known to cause very short TL in patients with DC,3 several studies found that patients with AA also had shorter TL than healthy individuals.4 Furthermore, sever- al cases of short TL in patients with non-DC IBMFS have been reported (Online Supplementary Table S3).3,5,10-15 Alter et al.5 previously reported that very short telomeres (<1st percentile of normal) were observed in five of 78 (6%) patients with non-DC IBMFS, although little overlap was seen in the distribution of TL between DC and non-DC IBMFS cases.
In this study we measured TL by standard flow-FISH in a cohort of BMF patients comprehensively and genetical- ly evaluated by next-generation sequencing. We defined TL < −1.71 SD of normal as a new criterion of “relatively short TL”; the proportions of patients who met this crite- rion were significantly higher in DC (91%) and non-DC cases (60%) than in AA cases (23%). These results sug- gest that TL measurement is useful as a screening test for DC and as a clinical diagnostic tool for non-DC IBMFS patients needing comprehensive genetic analysis.
One limitation of this study is its small sample size: we found that 73% (n=26) of IBMFS cases and 23% (n=107) of AA cases in this cohort had “relatively short TL.” A power calculation to check “relatively short TL” effective- ness in diagnosing IBMFS concluded that the power of 0.998 was high enough to support the assumption of a sufficient number of cases in this study.
A second limitation of the present study is the small number of non-DC cases (n=15), which was insufficient to discuss the significance of TL measurements in each IBMFS subtype. However, “relatively short TL” (<−1.71 SD) was observed in six of nine FA cases, two of four DBA cases, and one case of SDS (Figure 1B). The median TL were −1.84 SD (range, −4.74 to +2.05 SD), −0.89 SD (range, −2.83 to +1.21 SD), and −1.99 for FA, DBA, and SDS cases, respectively (Online Supplementary Table S2). These results support those in previous case reports demonstrating relatively short TL in FA, DBA, and SDS (Online Supplementary Table S3). Nevertheless, future studies in larger cohorts of patients are warranted.
This study confirms that a relatively short TL was pres- ent in a significant proportion of patients with DC and non-DC IBMFS, indicating the clinical diagnostic value of TL measurement in identifying patients who need further testing, particularly comprehensive genetic analysis.
Shunsuke Miwata,1 Atsushi Narita,1 Yusuke Okuno,1,2 Kyogo Suzuki,1 Motoharu Hamada,1 Taro Yoshida,1 Masayuki Imaya,1 Ayako Yamamori,1 Manabu Wakamatsu,1 Kotaro Narita,1 Hironobu Kitazawa,1 Daisuke Ichikawa,1 Rieko Taniguchi,1 Nozomu Kawashima,1 Eri Nishikawa,1 Nobuhiro Nishio,1,2 Seiji Kojima,1 Hideki Muramatsu1 and Yoshiyuki Takahashi1
1Department of Pediatrics, Nagoya University Graduate School of Medicine and 2Center for Advanced Medicine and Clinical Research, Nagoya University Hospital, Nagoya, Japan
Correspondence:
HIDEKI MURAMATSU - hideki-muramatsu@med.nagoya-u.ac.jp YOSHIYUKI TAKAHASHI - ytakaha@med.nagoya-u.ac.jp doi:10.3324/haematol.2021.278334
Received: January 22, 2021.
Accepted: April 13, 2021.
Pre-published: April 22, 2021.
Disclosures: no conflicts of interest to disclose.
Contributions: SM, AN and HM performed laboratory analyses, gathered clinical information, designed and conducted the research, analyzed data, and wrote the paper; MI, AY, MW, KN, HK, DI, RT and YO performed laboratory analyses; MH and YT gathered clinical information; KS, NK, EN, NN and SK conducted the research; YT directed the research and wrote the paper.
Acknowledgments: the authors acknowledge all the clinicians, patients, and their families involved in this study. The authors thank Ms. Yoshie Miura and Ms. Hiroko Ono for their valuable assistance.
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