Clinical Applications and Utility of a Precision Medicine Approach for Patients With Unexplained Cytopenias

Functional validation of TERT and TERC variants of uncertain significance in patients with short telomere syndromes

“…In our experience, a pathogenic variant in the coding sequence of a telomere-associated gene can be identified in only 40% of STS cases using current sequencing approaches, with the remaining cases either having no identifiable variant or possessing a variant(s) of uncertain significance (VUS) 1,3 . In addition, in some of these cases, the TL values were not conclusively shortened (i.e., not < first percentile in lymphocytes and/or granulocytes documented by a CLIA-certified FlowFISH assay) complicating the diagnosis.…”

“…In addition, in some of these cases, the TL values were not conclusively shortened (i.e., not < first percentile in lymphocytes and/or granulocytes documented by a CLIA-certified FlowFISH assay) complicating the diagnosis. At Mayo Clinic, we established a dedicated BMF clinic in collaboration with the center for Individualized Medicine and the division of Hematology, so as to leverage the latest NGS technologies and functional assays to assist patients with unexplained BMF syndromes, including STS-related marrow failure 3,4 . We have developed a systematic algorithmic approach to assess STS patients that includes TL testing by flowFISH and genomic assessment of STS-related gene mutations using an in-house designed targeted NGS panel (Supplementary Table 1).…”

“…Further, hTERC wraps around one side of this thumb and the DNA winds across the other side, so that any changes to the internal organization/ arrangement of this thumb may significantly alter function ( Fig. 1b) 3 . The third variant hTERT c,1765A > C; p.Ile589Leu (patient 3) affects a residue located in the helix near the hTERC interface possibly affecting stability of this interaction (Fig.…”

“…In addition to this information, further functional testing was pursued for these variants with the exception of hTERT c.2768 C > T; p.Pro923Leu (Patient 1), where we considered the evidence already available, including a published functional report, to be strong enough to consider this variant as being pathogenic 13 (more information in ref. 3 ). For the remaining patients with hTERT variants, we evaluated their telomerase activity using the TRAP assay 5 .…”

Hereditary Predisposition to Hematopoietic Neoplasms

“…At Mayo Clinic, our 2-year experience with a precision medicine clinic evaluating 68 patients with unexplained persistent (6 months) cytopenias (after exclusion of known infectious, autoimmune, toxic, and malignant causes; 29 [43%] with HPS) showed that genomic assessments resulted in an objective change in management in approximately 25% of tested patients. 147 Definition of a change in management included altered donor-selection strategy, conditioning regimen intensity, and/or initiation or discontinuation of a new drug and necessary both from therapeutic and supportive-care standpoints. Specific examples include use of danazol in short telomere syndromes 150 (although controversial other reports have raised questions whether danazol truly prevents telomere attrition 151,152 ), azithromycin prophylaxis to prevent atypical mycobacterial infections in patients with GATA2 haploinsufficiency syndromes, 153 use of granulocyte growth factor support for patients with severe congenital neutropenia, 154 and upcoming investigational strategies such as post-transcriptional modulation of TERC by inhibition of PAPD5 in dyskeratosis congenita 155 and gene therapy, 156 among others.…”