Correspondence: Identification of TINF2 gene mutations in adult Japanese patients with acquired bone marrow failure syndromes

Abstract

Mutations of the genes involved in human bone-marrow failure syndromes (BMFS) have been identified in components of the telomerase- and telomere-associated genes, including the TINF2 gene on chromosome 14q11·2, which encodes the 40 kDa TIN2 component of the telomere-associated shelterin protein complex (Calado & Young, 2008; Savage et al, 2008; Walne et al, 2008; Walne & Dokal, 2009). Clinically, it is very important to identify patients with pathogenic mutations in the telomere- or telomerase-associated genes, because these patients will probably exhibit refractoriness to conventional immunosuppressive therapy (IST) (Calado & Young, 2008). Several recent studies showed heterozygous TINF2 mutation in 1–5% of patients with acquired aplastic anaemia (AA) (Walne et al, 2008; Du et al, 2009). The subjects of these studies were Caucasian, Black and Hispanic. Analysis of the TINF2 gene among adult Asian populations of AA and myelodysplastic syndrome (MDS), to the best of our knowledge, had never been done. The largest controlled epidemiological study reported that the incidence of AA in the West was 2cases/million/year, but was about two- to three-fold higher in Asia (Issaragrisil et al, 2006). Therefore, we carried out an investigation to determine whether mutations in TINF2 could be found in our cohort of adult Japanese patients with acquired BMFS, and if so, at what frequency. We screened exon 6 of TINF2, as it was previously found to be a potential hotspot for disease-associated mutations (Walne et al, 2008; Du et al, 2009), among 142 Japanese patients who were diagnosed with acquired AA or MDS refractory anaemia between 1993 and 2006 at the Nippon Medical School Hospital. We excluded AA and MDS patients who were found to carry mutations in the telomerase TERC or TERT gene. We identified two AA patients (1·4%) with TINF2 heterozygous mutations, which were P283H and n865-866 di-nucleotide CC deletion (Fig 1A). The n865-866 di-nucleotide CC deletion in the TINF2 gene is a novel mutation that has not been previously identified. These mutations were not found in 300 healthy controls. Because of the lack of biological sample from the relatives of the patients as well as other tissues of the patients, it was not possible to determine whether these were segregational or germline mutations. Using Southern blotting technique, we compared the length of telomeres of mononuclear cells in AA patients who carried the TINF2 mutations to those of healthy age-matched controls. As shown in Fig 1B, AA patients with TINF2 mutations (Patients 1 and 2) showed much shorter telomere lengths than those of healthy age-matched controls. The clinical characteristics of these two patients with TINF2 mutation are shown in Table I. Both of the patients with TINF2 mutations were diagnosed with severe AA with no physical features of Dyskeratosis Congenita or its severe variant Hoyeraal-Hreidarsson syndrome (HH) (Walne et al, 2008) and showed no clinical response to IST. We attempted treatment of our patients with TINF2 mutations with metenolone, which is a dihydrotestosterone (DHT)-based anabolic steroid with androgenic properties, but they did not show any favourable clinical responses, unlike a previous report of favourable haematological response in BMFS patients with TERT mutations upon androgen treatment (Calado et al, 2009). In summary, we report here for the first time TINF2 natural mutations in 2/142 Japanese patients with acquired BMFS, which is at about the same frequency (1·4%) as reported in patients of other ethnic groups (Caucasian, Black and Hispanic) (Walne et al, 2008; Du et al, 2009). Identification of TINF2 mutations and telomere length measurements. (A) Gene mutations identified by direct sequencing. In the case of the n865-866 di-nucleotide CC deletion (Patient 2), the TINF2 PCR product was sub-cloned into pCR2·1-TOPO expression vector and sequenced. (B) telomere lengths of patients with TINF2 mutations. Patient 1: 3·1 kb, Patient 2: 4·9 kb. HY was the principal investigator and takes primary responsibility for the paper. HY, KI, JT, HT and KD recruited the patients. HY, KI, YM and FK performed the laboratory work for this study. HY, HL and KD analyzed the data and wrote the paper. The authors reported no potential conflicts of interest. This work was supported in part by grants from the American Cancer Society (RSG-06-162-01-GMC) and the AA&MDSIF to H.L.