Genetics of severe congenital neutropenia as a gateway to personalized therapy

Severe congenital neutropenias (SCNs) are rare diseases, and to date about 30 subtypes have been described according to their genetic causes. Standard care aims to prevent infections and limit the risk of leukemic transformation; however, several subtypes may have additional organ dysfunction(s), requiring specialized care. Granulocyte colony-stimulating factor and hematopoietic stem cell transplantation are now the bedrock of standard care. Better understanding of SCN mechanisms now offers the possibility of adapted therapy for some entities. An inhibitor of sodium glucose cotransporter, an antidiabetic drug, may attenuate glycogen storage disease type Ib and glucose-6-phosphatase catalytic subunit 3 neutropenias by clearing 1,5-anhydroglucitol, the precursor of the phosphate ester responsible for these SCNs. Chemokine receptor CXCR4 inhibitors contribute to reversing the leukocyte defect in warts, hypoglobulinemia, infections, and myelokathexis syndrome. All these new approaches use oral drugs, which notably improve quality of life. Additionally, improved research into clonal evolution has highlighted some ways to potentially prevent leukemia, such as stimulating somatic genetic rescue, a physiological process that might limit the risk of leukemic transformation.

Impaired myelopoiesis in congenital neutropenia: insights into clonal and malignant hematopoiesis

A common feature of both congenital and acquired forms of bone marrow failure is an increased risk of developing acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). Indeed, the development of MDS or AML is now the major cause of mortality in patients with congenital neutropenia. Thus, there is a pressing clinical need to develop better strategies to prevent, diagnose early, and treat MDS/AML in patients with congenital neutropenia and other bone marrow failure syndromes. Here, we discuss recent data characterizing clonal hematopoiesis and progression to myeloid malignancy in congenital neutropenia, focusing on severe congenital neutropenia (SCN) and Shwachman-Diamond syndrome. We summarize recent studies showing excellent outcomes after allogenic hematopoietic stem cell transplantation for many (but not all) patients with congenital neutropenia, including patients with SCN with active myeloid malignancy who underwent transplantation. Finally, we discuss how these new data inform the current clinical management of patients with congenital neutropenia.

Pediatric single large-scale mtDNA deletion syndromes: The power of patient reported outcomes

There is a limited understanding of system-level clinical outcomes and interventions associated with single large-scale mitochondrial DNA deletion syndromes (SLSMDS). Additionally, no research exists that describes patient reported outcomes (PROs) of children with SLSMDS. A global and observational registry was established to understand the multi-systemic course of SLSMDS and track clinical outcomes. The development and design of the registry is described. Demographic characteristics, history and diagnoses, and system level prevalence of problems and interventions are reported for 42 children. System level problems and interventions include information on the following body systems: audiology, cardiac, endocrine, gastrointestinal (including pancreatic and hepatobiliary system), hematological, metabolic, neurological (including autonomic, mobility, & learning), ophthalmic, psychiatric, renal, and respiratory. Results emphasize the need of patient registries and suggest that the diagnostic odyssey and burden of disease for children with SLSMDS is significant. System-level findings may help families and clinical providers with diagnosis, prognostication, and treatment. A multidisciplinary team of clinical experts with a central coordinating specialist for children with SLSMDS is recommended.

Special pre- and posttransplant considerations in inherited bone marrow failure and hematopoietic malignancy predisposition syndromes

Advances in the diagnosis and treatment of inherited bone marrow failure syndromes (IBMFS) have provided insight into the complexity of these diseases. The diseases are heterogeneous and characterized by developmental abnormalities, progressive marrow failure, and predisposition to cancer. A correct diagnosis allows for appropriate treatment, genetic counseling, and cancer surveillance. The common IBMFSs are Fanconi anemia, dyskeratosis congenita, and Diamond-Blackfan anemia. Hematopoietic cell transplantation (HCT) offers curative treatment of the hematologic complications of IBMFS. Because of the systemic nature of these diseases, transplant strategies are modified to decrease immediate and late toxicities. HCT from HLA-matched related or unrelated donors offers excellent survival for young patients in aplasia. Challenges include the treatment of adults with marrow aplasia, presentation with myeloid malignancy regardless of age, and early detection or treatment of cancer. In this article, I will describe our approach and evaluation of patients transplanted with IBMFS and review most frequent complications before and after transplant.

CRISPR-Cas9-Mediated ELANE Mutation Correction in Hematopoietic Stem and Progenitor Cells to Treat Severe Congenital Neutropenia

Severe congenital neutropenia (SCN) is a monogenic disorder. SCN patients are prone to recurrent life-threatening infections. The main causes of SCN are autosomal dominant mutations in the ELANE gene that lead to a block in neutrophil differentiation. In this study, we use CRISPR-Cas9 ribonucleoproteins and adeno-associated virus (AAV)6 as a donor template delivery system to repair the ELANEL172P mutation in SCN patient-derived hematopoietic stem and progenitor cells (HSPCs). We used a single guide RNA (sgRNA) specifically targeting the mutant allele, and an sgRNA targeting exon 4 of ELANE. Using the latter sgRNA, ∼34% of the known ELANE mutations can in principle be repaired. We achieved gene correction efficiencies of up to 40% (with sgELANE-ex4) and 56% (with sgELANE-L172P) in the SCN patient-derived HSPCs. Gene repair restored neutrophil differentiation in vitro and in vivo upon HSPC transplantation into humanized mice. Mature edited neutrophils expressed normal elastase levels and behaved normally in functional assays. Thus, we provide a proof of principle for using CRISPR-Cas9 to correct ELANE mutations in patient-derived HSPCs, which may translate into gene therapy for SCN.

Adult-onset Repeat Rhabdomyolysis with a Very Long-chain Acyl-CoA Dehydrogenase Deficiency Due to Compound Heterozygous ACADVL Mutations

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is a genetic disorder of fatty acid beta oxidation that is caused by a defect in ACADVL, which encodes VLCAD. The clinical presentation of VLCAD deficiency is heterogeneous, and either a delayed diagnosis or a misdiagnosis may sometimes occur. We herein describe a difficult-to-diagnose case of the muscle form of adult-onset VLCAD deficiency with compound heterozygous ACADVL mutations including c.790A>G (p.K264E) and c.1246G>A (p.A416T).

Effects of fasting, feeding and exercise on plasma acylcarnitines among subjects with CPT2D, VLCADD and LCHADD/TFPD

BACKGROUND

The plasma acylcarnitine profile is frequently used as a biochemical assessment for follow-up in diagnosed patients with fatty acid oxidation disorders (FAODs). Disease specific acylcarnitine species are elevated during metabolic decompensation but there is clinical and biochemical heterogeneity among patients and limited data on the utility of an acylcarnitine profile for routine clinical monitoring.

METHODS

We evaluated plasma acylcarnitine profiles from 30 diagnosed patients with long-chain FAODs (carnitine palmitoyltransferase-2 (CPT2), very long-chain acyl-CoA dehydrogenase (VLCAD), and long-chain 3-hydroxy acyl-CoA dehydrogenase or mitochondrial trifunctional protein (LCHAD/TFP) deficiencies) collected after an overnight fast, after feeding a controlled low-fat diet, and before and after moderate exercise. Our purpose was to describe the variability in this biomarker and how various physiologic states effect the acylcarnitine concentrations in circulation.

RESULTS

Disease specific acylcarnitine species were higher after an overnight fast and decreased by approximately 60% two hours after a controlled breakfast meal. Moderate-intensity exercise increased the acylcarnitine species but it varied by diagnosis. When analyzed for a genotype/phenotype correlation, the presence of the common LCHADD mutation (c.1528G > C) was associated with higher levels of 3-hydroxyacylcarnitines than in patients with other mutations.

CONCLUSIONS

We found that feeding consistently suppressed and that moderate intensity exercise increased disease specific acylcarnitine species, but the response to exercise was highly variable across subjects and diagnoses. The clinical utility of routine plasma acylcarnitine analysis for outpatient treatment monitoring remains questionable; however, if acylcarnitine profiles are measured in the clinical setting, standardized procedures are required for sample collection to be of value.

Exosomes derived from mesenchymal stem cells improved function and survival of neutrophils from severe congenital neutropenia patients in vitro

Severe congenital neutropenia (SCN) is described by the absolute neutrophil counts less than 500 cells/mm³, bacterial infections, and an arrest of neutrophil differentiation. So, effective strategies for improving the function and lifespan of the existing neutrophils in these patients are necessary. Mesenchymal stem cells (MSCs) have supportive effects on neutrophils. Recently, it was determined that MSCs exert their effects, mostly by secreting soluble factors and exosomes. So, in this study, neutrophils were isolated from the bloodstream of healthy donors and SCN patients and cultured with medium, MSC-exosomes or MSC-conditioned media (MSC-CM). Then, the effects of the two treatments on neutrophil respiratory burst, apoptosis and phagocytosis percentage were assessed using nitro blue tetrazolium (NBT) assay, annexin V-propidium iodide (PI) and Giemsa staining, respectively. Both treatments could significantly augment respiratory burst of neutrophils from SCN patients and healthy donors. But, only CM could significantly enhance phagocytosis index. About the lifespan of neutrophils, only exosomes could significantly enhance it in both groups. Based on these results, both exosomes and CM derived from MSCs could be attractive candidates for rescuing SCN patients from serious infections.

AAV9 gene replacement therapy for respiratory insufficiency in very-long chain acyl-CoA dehydrogenase deficiency

Very-long chain acyl-CoA dehydrogenase (VLCAD) deficiency (VLCADD) is an autosomal recessive disorder of fatty acid oxidation. Fatty acids are a major source of energy during catabolic stress, so the absence of VLCAD can result in a metabolic crises and respiratory insufficiency. The etiology of this respiratory insufficiency is unclear. Thus, our aims were: (1) to characterize respiratory pathophysiology in VLCADD mice (VLCAD^-/- ), and (2) to determine if AAV9-mediated gene therapy improves respiratory function. For the first aim, VLCAD^-/- and wild-type (WT) mice underwent an exercise/fast "stress protocol" and awake spontaneous breathing was evaluated using whole-body plethysmography (WBP) both at baseline and during a hypercapnic respiratory challenge (FiO₂ : 0.21; FiCO₂ : 0.07; nitrogen balance). During hypercapnia, VLCAD ^-/- mice had a significantly lower frequency, tidal volume, minute ventilation, and peak inspiratory and expiratory flow, all of which indicate respiratory insufficiency. Histologically, the cardiac and respiratory muscles of stressed VLCAD ^-/- animals had an accumulation of intramyocellular lipids. For the second aim, a single systemic injection of AAV9-VLCAD gene therapy improved this respiratory pathology by normalizing breathing frequency and enhancing peak inspiratory flow. In addition, following gene therapy, there was a moderate reduction of lipid accumulation in the respiratory muscles. Furthermore, VLCAD protein expression was robust in cardiac and respiratory muscle. This was confirmed by immuno-staining with anti-human VLCAD antibody. In summary, stress with exercise and fasting induces respiratory insufficiency in VLCAD^-/- mice and a single injection with AAV9-VLCAD gene therapy ameliorates breathing.

A Case of Papillary Thyroid Carcinoma and Kostmann Syndrome: A Genomic Theranostic Approach for Comprehensive Treatment

BACKGROUND Theranostics is a combined diagnostic and treatment approach to individualized patient care. Kostmann syndrome, or severe congenital neutropenia, is an autosomal recessive disease that affects the production of neutrophils. Papillary thyroid carcinoma (PTC) is the most common type of thyroid malignancy associated with gene alterations, including in the mitogen-activated protein kinase (MAPK) signaling pathway gene. Translocation of the ETS variant 6/neurotrophic receptor tyrosine kinase 3 (ETV6/NTRK3) gene has been implicated in radiation-induced and pediatric forms of thyroid carcinoma but has rarely been described in sporadic PTC. This report is of a case of PTC in a patient with Kostmann syndrome associated with ETV6/NTRK3 gene translocation. CASE REPORT A 32-year-old woman with a history of Kostmann syndrome, acute myeloid leukemia (AML), and chronic graft versus host disease (GVHD) was diagnosed with PTC with cervical lymph node metastases and soft tissue invasion following total thyroidectomy and bilateral modified radical neck dissection. Her postoperative radioactive iodine (RAI) scan confirmed lymph node metastasis. Gene expression studies identified increased expression of iodine-handling genes and ETV6/NTRK3 gene fusion. Because of the bone marrow compromise due to Kostmann syndrome and AML, a careful genomic and molecular analysis was performed to guide therapy. CONCLUSIONS This is the first reported case of the association between PTC, Kostmann syndrome, and ETV6/NTRK3 gene translocation in which multimodality treatment planning was optimized by genomic profiling.