Successful cord blood transplantation for del7q myelodysplastic syndrome in Pearson marrow pancreas syndrome.

Pearson marrow pancreas syndrome (PS) is a multisystem bone marrow failure (BMF) disorder caused by deletions in mitochondrial DNA (mtDNA). Infant-onset transfusion-dependent pancytopenia, immune defects, and metabolic crises result in early mortality. However, PS often goes undiagnosed, and its rarity, comorbidities, and occasional spontaneous hematologic improvement deter timely consideration of hematopoietic stem cell transplantation (HSCT). Here, we report successful cord blood transplantation with 4 years of follow-up for a child with PS who developed myelodysplastic syndrome (MDS) with deletion of chromosome 7q (del7q). By longitudinal quantitation of mutant mtDNA in peripheral blood, we demonstrate the threshold of heteroplasmy correlating with hematologic recovery and its trajectory in myeloid versus lymphoid lineages after HSCT. The case illustrates that PS is an MDS/leukemia predisposition syndrome warranting surveillance and early HSCT consultation, and documents the molecular and clinical evolution of PS-associated features after complete replacement of the hematopoietic system. In PS, a deletion occurs in one copy of the mtDNA amongst many, presumably in the female germ cell or oocyte.1, 2 The so-called single large-scale mitochondrial DNA deletion (SLSMD) is amplified by unknown means to constitute varying proportions of mutant versus normal mtDNA, termed heteroplasmy, which accumulate differently in various tissues during development.3 The consequence is a multisystem disorder with phenotypic variability amongst SLSMD patients.4 PS is a severe form characterized by early-onset BMF, metabolic disorder, and pancreatic and renal dysfunction.5 For patients who survive the early manifestations of PS, symptoms may progress into cardiac, muscular, and neurological defects characteristic of later-onset SLSMD diseases such as Kearns-Sayre Syndrome (KSS) and Progressive External Ophthalmoplegia (PEO). PS is frequently misdiagnosed as Diamond-Blackfan anemia due to severe anemia in the neonatal period.5-7 Spontaneous hematologic improvement can be seen in both disorders. In PS, durable transfusion-independence occurring in the first few years of life is presumed to be due to a selection against mutant mtDNA in hematopoietic stem and progenitor cells (HSPC), which have a high capacity for turnover, thus reducing the burden of mutant mtDNA below a threshold of mitochondrial dysfunction.8, 9 The expectation of spontaneous hematologic improvement has been used to argue against definitive but high-risk treatment for BMF via HSCT.10, 11 However, the timeline of remission remains unpredictable, and in the interim PS patients may suffer life-threatening complications of BMF and transfusion support, including infections, iron overload, and allosensitization. Moreover, hematopoiesis in the face of chronic mitochondrial dysfunction could be maladaptive including transformation to MDS or leukemia, as is seen with chronic marrow stress in other inherited BMF syndromes. Here, we report a patient with PS who experienced spontaneous hematologic improvement but later developed MDS with del7q and underwent successful HSCT. The patient was born at 41 weeks gestational age by Caesarean section due to non-reassuring fetal heart tracing and was found to have respiratory distress. Initial complete blood count showed a hemoglobin 6.0 g/dL, with white blood cell count (WBC) 7000/μL, absolute neutrophil count (ANC) 2800/μL, platelet count 360 000/μL, and reticulocyte count 47 100/μL. His workup was notable for hepatomegaly, but no ABO blood type incompatibility or signs of bleeding. He received packed red blood cells (RBC) and improved with discharge on the fourth day of life. Bone marrow evaluation was performed for persistent anemia at 5 weeks of age and showed a cellular bone marrow with myeloid predominance, vacuolation of immature myeloid and erythroid progenitors, and occasional ringed sideroblasts. A workup for congenital sideroblastic anemia ultimately demonstrated an ~5 kilobase mtDNA deletion (m.10382_15406) detected in peripheral blood by next-generation sequencing and quantified as approximately 98% of mtDNA, establishing the diagnosis of PS. The patient continued to be RBC transfusion-dependent until approximately 14 months old. During that time, he experienced severe neutropenia (ANC range 80–380/μL) and thrombocytopenia (platelet nadir 59 000/μL). He did not have any major infectious complications, bleeding, or need for platelet transfusions. He had elevated lactate levels with febrile illnesses, and was maintained on enteral bicarbonate supplementation. After 14 months of age, his blood counts improved and he became RBC transfusion-independent, with hemoglobin reaching the 11–12 g/dL range. His ANC and platelet counts normalized in the year that followed, and he was felt to be in a hematologic remission (Figure 1A). Serial mtDNA assessment in peripheral blood by Southern blot showed a decrease in mutant mtDNA burden over this time (Figure 1B,C). At 4 years of age, the patient presented for participation in a clinical trial of maternal mitochondrial augmentation therapy using his own HSPCs.12 A bone marrow examination unexpectedly demonstrated del7q abnormality in 30% of cells by fluorescence in situ hybridization (FISH) and in 13 of 20 metaphases by karyotype, confirmed by repeat examination of bone marrow and peripheral blood. In retrospect the patient's platelet count trajectory was downward in the preceding year with intact WBC and hemoglobin (Figure 1A). The patient was deemed ineligible for the autologous stem cell trial and referred for allogeneic HSCT. An HLA-matched cord blood unit was available from the patient's younger sibling, who did not have detectable mutant mtDNA in the blood. The conditioning regimen was busulfan 0.8 mg/kg every 6 h (days −7 to −4) with a target area under the curve of 1300–1450 μmol*min/L per dose, fludarabine 40 mg/m2 daily (days −5 to −2), and graft versus host disease (GVHD) prophylaxis was tacrolimus and mycophenolate mofetil. Venous blood gases and lactate levels were monitored daily with adjustments of sodium bicarbonate supplementation in consultation with the metabolic disorders service. Neutrophil engraftment occurred at day+16, and the initial transplant course was uncomplicated. The patient however developed late sinusoidal obstructive syndrome (SOS) on day+29 and required defibrotide therapy and peritoneal drain placement, recovering on day+55 without sequelae. The post-transplant course was complicated by an episode of polymicrobial bacteremia on day+90 treated successfully, and the patient recovered uneventfully. The patient was weaned off of GVHD prophylaxis and antibiotics without complications. Hematologic parameters remained stable over 3.5 years of follow-up. Engraftment monitoring showed full donor myeloid chimerism from earliest assessments post-HSCT, with initial mixed donor lymphoid chimerism ultimately becoming full donor (Figure 1D). Peripheral blood mtDNA assessment by Southern blot post-HSCT showed the expected rapid depletion of mutant mtDNA; however, the patient's deletion could be detected by PCR even at 3 years post-HSCT. By highly sensitive ddPCR quantitation of heteroplasmy on peripheral blood cells fractionated by flow cytometry, the residual mutant mtDNA was determined to be due to recipient T lymphocytes, and decreased in conjunction with establishment of full donor lymphoid engraftment (Figure 1E–G). The patient's post-HSCT course was characterized by clinical manifestations attributable to PS evolving into KSS. These included ptosis, low facial tone, proximal muscle weakness, mild incoordination for age, and sensorineuronal hearing loss reflective of myopathy and neuropathy; hypoparathyroidism and renal tubulopathy treated with electrolyte supplements; and nutritional deficiency managed with pancreatic enzyme replacement and G-tube feeding but no longer requiring bicarbonate supplementation. The patient remains alive and active 4 years post-HSCT with no evidence of GVHD or relapse. This case illustrates several important points about PS, an ultra-rare and underdiagnosed BMF disorder. First, the patient was incidentally diagnosed with del7q MDS while being evaluated for clinical trial participation. Despite limited literature, the number of cases reporting MDS/AML in PS warrants its designation as a childhood hematologic cancer predisposition syndrome (Table S1). Akin to other BMF disorders with MDS/AML propensity, a bone marrow surveillance plan should be employed by hematologists on a case-by-case basis, balancing clinical concern versus procedural risk, to evaluate for transformation and potential HSCT, including patients in hematologic “remission.” Second, the patient's younger, unaffected sibling's cord blood was successfully utilized as an ideal HLA-matched graft source. PS primarily occurs de novo in one child with rare, if any, recurrence risk in families. Early referral to the HSCT service would enable evaluation of donor availability and, if needed, timely counseling and family planning for potential pre-implantation HLA matching and cord blood banking. Third, despite ablative conditioning using busulfan for MDS in this patient, careful metabolic monitoring enabled HSCT without unanticipated toxicities, including successful management of SOS and bacterial infections. Our case is the third report of successful HSCT for children with PS and MDS, whereas mortality following transplantation was reported by three others (Table S1).13-16 Our report suggests PS patients may not be subject to toxicities above and beyond those seen in other BMF syndromes, and may benefit from earlier HSCT consideration for BMF and to prevent MDS/AML, prior to onset of multisystem disease. Finally, our report and others raise the question of potential systemic benefits of HSCT in PS. While the natural history of PS is unclear and varies considerably between individuals, our patient has been off bicarbonate supplementation following allogeneic HSCT, reminiscent of the metabolic improvement reported by Hoyoux et al. (Table S1). One possible mechanism for systemic effects after HSCT could be eliminating the large burden of hematopoietic cells with high heteroplasmy and anaerobic metabolism. In the setting of busulfan conditioning, chimerization of HSPC-derived, tissue-resident cells (e.g., Kupffer cells, microglial cells) is known to provide the benefit of metabolic cross-correction after HSCT in enzymopathies such as adrenoleukodystrophy and Hurler's syndrome.17 An analogous impact of HSCT in PS could be by replacing dysfunctional cells rather than providing an enzymatic function in trans. The potential for non-hematologic or systemic benefits remains speculative and will be determined by ongoing observation of PS patients who have undergone allogeneic HSCT, which is critical to inform prospects for innovative gene and cellular therapy approaches. Z.H.B., S.M.D., and S.A. designed and performed the research, and wrote the manuscript. Z.H.B. performed experiments and analyzed molecular data. E.J., P.L.M., S.B.P., and M.D.F. provided samples and/or clinical information and feedback on the manuscript. We thank the patient and family for participation in research. We thank A. Shimamura and the Boston Children's Hospital Bone Marrow Failure/Myelodysplastic Syndrome Registry (National Institutes of Health (NIH) grant R21DK099808). This work was supported by funding from the Champ Foundation (to S.A. and S.B.P.), Associazione Luigi Comini Onlus (to S.A.), NIH RC2DK122533 (to M.D.F), and NIH R01DK107716 (to S.A.). The authors declare no competing financial interests. The data that support the findings of this study are available from the corresponding author upon reasonable request. Data S1. Supporting Information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.