LAUSR

Dear Editor, Inherited bone marrow failure syndromes (IBMFS) are a heterogeneous group of genetic blood disorders in which there is usually some form of aplastic anemia, associatedwith a family history of the same disorder. In addition, patients with IBMFS have a high risk of malignancies [1]. Some IBMFS have excessively short telomeres at the peripheral nucleated blood cell level, referred to as telomeropathies. The discovery of loss-offunction mutations in genes of telomerase complex (TERC and TERT) established a genetic etiology for telomere attrition in these patients [2, 3]. Several TERC variants, more than 40 nucleotide changes and small deletions, in patients with bone marrow failure have been described [4]. TERC gene, encoding the RNA component of telomerase, spans 451 nucleotides and comprises one non-coding exon that contains several conserved regions essential for its stability. Vertebrate telomerase RNA is composed by four highly conserved structural regions: pseudoknot domain, CR4-CR5 domain, box H/ACA domain, and CR7 domain [5, 6]. The mutations are distributed throughout TERC molecule, indicating that all domains contribute to function and that intricately base-paired structure is critical for its biologic activity [7, 8]. Here, we report on the case of a 33-year-old female affected by a severe anemia and pancytopenia since the age of 3. Family history is positive for blood disorders. Patient’s mother was diagnosed with a severe anemia at the age of 20 and died for a lymphoma, whereas maternal grandfather died for an unspecified form of blood cancer at the age of 80. A bone marrow biopsy performed on our patient showed a markedly hypocellular marrow with a reduction of all cell lines, consistent with the diagnosis of aplastic anemia. Molecular analysis of a panel of genes associated with hereditary anemia was performed by next generation sequencing on a sample of genomic DNA from peripheral blood. Genetic testing revealed a novel heterozygous variant in TERC gene, n.179 T>A (NG_016363.1). The variant was confirmed and checked in healthy father and brother for segregation by direct Sanger sequencing (Fig. 1a). Mother’s DNA sample was not available but we suppose that she harbored the n.179 T>A TERC variant based on of her hematological history. Analysis of mean telomere lengths by Q-FISH in metaphase spreads established from patient’s lymphocytes showed significantly shorter telomeres when compared with those of seven age-matched controls (Fig. 1b, c) confirming that the identified TERC variant has functional implications. Moreover, when compared to normal controls, the patient displayed also a very higher percentage of undetectable and short telomeres (Fig. 1d). We used structural and molecular modeling to gain insight into the effects of the identified TERC variant. The n.179 T>A nucleotide substitution destroys the complementarity with nucleotide A111 in the stem 2 (P3) of the hTER pseudoknot (Fig. 1e), thus breaking the W-C base pairing in this stem. Furthermore, distortions might occur in the arrangements of nearby paired residues to accommodate the larger replacing purine nucleotide. In yeast, base pairing of the central region of stem 2 of the conserved pseudoknot is important for in vivo binding of Est2p (TERT) and telomere maintenance [9]. Of note, both nucleotides flanking 179 T are sites of know pathogenic mutations, 178 G>A and 180 C>T [10]. We propose a pathogenic role for the 179 T>A replacement based on the structural changes envisaged in the central portion of stem 2, which is a region important for the catalytic activity of the * M. Rinelli [email protected]