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NHEJ1-patients develop severe progressive lymphocytopenia and premature aging of hematopoietic stem cells (HSCs) at a young age. Here we show a patient with a homozygous-NHEJ1 mutation identified by whole exome-sequencing that developed severe pancytopenia and bone marrow aplasia correlating with the presence of short telomeres. The mutation resulted in a truncated protein. In an attempt to identify the mechanism behind the short telomere phenotype found in the NHEJ1-patient we downregulated NHEJ1 expression in 293T and CD34+cells. This downregulation resulted in reduced telomerase activity and decreased expression of several telomerase/shelterin genes. Interestingly, cell lines derived from two other NHEJ1-deficient patients with different mutations also showed increased p21 expression, inhibition in expression of several telomerase complex genes and shortened telomeres. Decrease in expression of telomerase/shelterin genes did not occur when we inhibited expression of other NHEJ genes mutated in SCID patients: DNA-PK, Artemis or LigaseIV. Because premature aging of HSCs is observed only in NHEJ1 patients, we propose that is the result of senescence induced by decreased expression of telomerase/shelterin genes that lead to an inhibition of telomerase activity. Previous reports failed to find this connection because of the use of patient´s cells immortalized by TERT expression or recombined telomeres by ALT pathway. In summary, defective regulation of telomere biology together with defective V(D)J recombination can negatively impact on the evolution of the disease in these patients. Identification of telomere shortening is important since it may open new therapeutic interventions for these patients by treatments aimed to recover the expression of telomerase genes., R.P. laboratory is partially funded by grant P14-01495 (Fondo de Investigaciones Sanitarias, Instituto de Salud Carlos III, Spain supported by FEDER funds) and ER15PR07ACC114/757 from CIBERER. J.B. laboratory is funded by PI12/00070 and PI16/00440 (FIS) supported by FEDER funds and ER14PROACC13G706. C.M-G granted by the CIBERER. P.R is a scientist from Centre National de la Recherche Scientifique (CNRS). P.R and J-P.V are from a laboratory “Labellise´ La Ligue”.

Background Congenital sideroblastic anemias are rare disorders with several genetic causes; they are characterized by erythroblast mitochondrial iron overload, differ greatly in severity and some occur within a syndrome. The most common cause of non-syndromic, microcytic sideroblastic anemia is a defect in the X-linked 5-aminolevulinate synthase 2 gene but this is not always present. Recently, variations in the gene for the mitochondrial carrier SLC25A38 were reported to cause a non-syndromic, severe type of autosomal-recessive sideroblastic anemia. Further evaluation of the importance of this gene was required to estimate the proportion of patients affected and to gain further insight into the range and types of variations involved.Design and Methods In three European diagnostic laboratories sequence analysis of SLC25A38 was performed on DNA from patients affected by congenital sideroblastic anemia of a non-syndromic nature not caused by variations in the 5-aminolevulinate synthase 2 gene.Results Eleven patients whose ancestral origins spread across several continents were homozygous or compound heterozygous for ten different SLC25A38 variations causing premature termination of translation (p.Arg117X, p.Tyr109LeufsX43), predicted splicing alteration (c.625G>C; p.Asp209His) or missense substitution (p.Gln56Lys, p.Arg134Cys, p.Ile147Asn, p.Arg187Gln, p.Pro190Arg, p.Gly228Val, p.Arg278Gly). Only three of these variations have been described previously (p.Arg117X, p.Tyr109LeufsX43 and p.Asp209His). All new variants reported here are missense and affect conserved amino acids. Structure modeling suggests that these variants may influence different aspects of transport as described for mutations in other mitochondrial carrier disorders.Conclusions Mutations in the SLC25A38 gene cause severe, non-syndromic, microcytic/hypochromic sideroblastic anemia in many populations. Missense mutations are shown to be of importance as are mutations that affect protein production. Further investigation of these mutations should shed light on structure-function relationships in this protein.

Background: Eltrombopag (EPAG), an oral thrombopoietin receptor agonist, is approved for treating thrombocytopenia in adults with chronic immune thrombocytopenia (ITP) with insufficient response to prior therapy. Pooled data from 2 similarly designed, randomized, double-blind, placebo (PBO)-controlled studies investigating safety and efficacy of EPAG in pediatric ITP are presented here. Methods: Subjects aged 1 to Results: A total of 174 subjects were enrolled in both studies; 171 received ≥1 dose of EPAG. 159 subjects were randomized (intent-to-treat population), and 157 received ≥1 dose of randomized study treatment (safety population). In the randomized period, 3 EPAG and 1 PBO subject discontinued study treatment, of which 2 EPAG and 1 PBO discontinued due to adverse events (AEs). In the OL-EPAG period, an additional 14 EPAG subjects discontinued study treatment, 6 due to AEs. Males comprised 47% of the EPAG and PBO groups and 20% and 24% were East Asians, respectively. Most subjects (93%) were diagnosed with ITP for ≥12 months, and 13% were receiving ITP medications at baseline. The majority of subjects (81%) received ≥2 prior ITP therapies. Most subjects (59%) had a baseline platelet count Randomized Period A higher proportion of EPAG versus PBO subjects (62% vs 24%; P < 0.001) achieved a response with platelet counts ≥50 Gi/L at least once between weeks 1–6 (Cohort 1, 64% vs 11%; Cohort 2, 64% vs 27%; Cohort 3, 54% vs 36%, respectively). At each week, a higher proportion of EPAG subjects had a response versus PBO (Fig. 1). A lower proportion of EPAG subjects (13%) received rescue treatment compared with PBO subjects (31%; P = 0.009). The odds of having World Health Organization (WHO) bleeding grades 1–4 (0.19; P = 0.011) and clinically significant (WHO grades 2–4) bleeding (0.29; P = 0.007) were lower for EPAG versus PBO subjects. EPAG-Only Period Sustained reduction or discontinuation of baseline ITP medications, primarily corticosteroids, was achieved by 50% of subjects; 81% of subjects had a platelet count response at least once; 52% (n = 80/154) had a platelet count response for ≥50% of assessments; and 38% (n = 58/154) responded for ≥75% of assessments. For >13 of 24 weeks, 47% of subjects achieved responses (Fig. 2). The median average daily dose for EPAG-exposed patients in Cohorts 1, 2, and 3 were 64.0 mg (0.93 mg/kg), 57.6 mg (1.50 mg/kg), and 37.0 mg (2.02 mg/kg), respectively. AEs Similar proportions of subjects in the EPAG and PBO groups reported an AE during the randomization period. The most common AEs (≥10% of subjects) were headache, upper respiratory tract infection, and nasopharyngitis in the EPAG group, and headache, epistaxis, and vomiting in the PBO group. Serious AEs (SAEs) were reported in 8% of EPAG subjects versus 12% of PBO subjects. No SAEs were reported by >1 subject in either treatment group except epistaxis, which was reported by 2 subjects in the PBO group. No SAEs were common to both treatment groups. In the randomized period, an ALT elevation of ³3 x ULN occurred in 5 (4.7%) subjects in the EPAG group and no subjects in the PBO group. In the OL period, there were an additional 7 subjects with ALT ³3 x ULN. All elevations resolved either while still on treatment or after discontinuation of study treatment. Overall, the hepatobiliary laboratory findings were mostly mild, reversible, and not accompanied by impaired liver function. Fewer EPAG than PBO subjects reported bleeding AEs (17% vs 36%, respectively). No thromboembolic events were reported. Cataract events were experienced by 2 subjects who received EPAG; both had used corticosteroids and 1 had pre-existing cataracts. Conclusions: EPAG was safe and raised platelet counts in 62% of pediatric patients with persistent and chronic ITP during the randomized phase. Treatment with EPAG was well tolerated in both studies as evidenced by the low incidence of treatment discontinuations due to AEs. Disclosures Bussel: Shionogi: Membership on an entity's Board of Directors or advisory committees, Research Funding; Rigel: Honoraria; Novartis: Honoraria; Ligand: Membership on an entity's Board of Directors or advisory committees, Research Funding; Immunomedics: Research Funding; IgG of America: Research Funding; GlaxoSmithKline: Equity Ownership, Honoraria, Research Funding; Genzyme: Research Funding; Eisai, Inc.: Research Funding; Cangene: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Amgen: Equity Ownership, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Symphogen: Membership on an entity's Board of Directors or advisory committees; Sysmex: Research Funding. Off Label Use: Eltrombopag is a thrombopoietin receptor agonist approved for the treatment of thrombocytopenia in adults with chronic ITP. Use in children and adolescents will be discussed.. Grainger:GlaxoSmithKline: Honoraria; Baxter: Honoraria, Research Funding; Amgen: Honoraria. Pongtanakul:GlaxoSmithKline: Research Funding. Komvilaisak:GlaxoSmithKline: I am an investigator on this study. Other. Sosothikul:CSL Behring: Research Funding; GlaxoSmithKline: Research Funding. Drelichman:GlaxoSmithKline: I am investigator on this study. Other. David:GlaxoSmithKline: Research Funding. Marcello:GlaxoSmithKline: Employment. Iyengar:GlaxoSmithKline: Employment. Chan:GlaxoSmithKline: Employment. Chagin:GlaxoSmithKline: Employment. Theodore:GlaxoSmithKline: Employment, Equity Ownership. Bakshi:GlaxoSmithKline: Employment, Equity Ownership. Bailey:GlaxoSmithKline: Employment, Equity Ownership.