Familial Myeloproliferative Disorders

Review on Familial Myeloproliferative Disorders, with data on clinics, and the genes involved

Genetic Alterations of the Thrombopoietin/MPL/JAK2 Axis Impacting Megakaryopoiesis

Megakaryopoiesis is an original and complex cell process which leads to the formation of platelets. The homeostatic production of platelets is mainly regulated and controlled by thrombopoietin (TPO) and the TPO receptor (MPL)/JAK2 axis. Therefore, any hereditary or acquired abnormality affecting this signaling axis can result in thrombocytosis or thrombocytopenia. Thrombocytosis can be due to genetic alterations that affect either the intrinsic MPL signaling through gain-of-function (GOF) activity (MPL, JAK2, CALR) and loss-of-function (LOF) activity of negative regulators (CBL, LNK) or the extrinsic MPL signaling by THPO GOF mutations leading to increased TPO synthesis. Alternatively, thrombocytosis may paradoxically result from mutations of MPL leading to an abnormal MPL trafficking, inducing increased TPO levels by alteration of its clearance. In contrast, thrombocytopenia can also result from LOF THPO or MPL mutations, which cause a complete defect in MPL trafficking to the cell membrane, impaired MPL signaling or stability, defects in the TPO/MPL interaction, or an absence of TPO production

Congenital hyperinsulinism: current trends in diagnosis and therapy

Congenital hyperinsulinism (HI) is an inappropriate insulin secretion by the pancreatic β-cells secondary to various genetic disorders. The incidence is estimated at 1/50, 000 live births, but it may be as high as 1/2, 500 in countries with substantial consanguinity. Recurrent episodes of hyperinsulinemic hypoglycemia may expose to high risk of brain damage. Hypoglycemias are diagnosed because of seizures, a faint, or any other neurological symptom, in the neonatal period or later, usually within the first two years of life. After the neonatal period, the patient can present the typical clinical features of a hypoglycemia: pallor, sweat and tachycardia. HI is a heterogeneous disorder with two main clinically indistinguishable histopathological lesions: diffuse and focal. Atypical lesions are under characterization. Recessive ABCC8 mutations (encoding SUR1, subunit of a potassium channel) and, more rarely, recessive KCNJ11 (encoding Kir6.2, subunit of the same potassium channel) mutations, are responsible for most severe diazoxide-unresponsive HI. Focal HI, also diazoxide-unresponsive, is due to the combination of a paternally-inherited ABCC8 or KCNJ11 mutation and a paternal isodisomy of the 11p15 region, which is specific to the islets cells within the focal lesion. Genetics and 18F-fluoro-L-DOPA positron emission tomography (PET) help to diagnose diffuse or focal forms of HI. Hypoglycemias must be rapidly and intensively treated to prevent severe and irreversible brain damage. This includes a glucose load and/or a glucagon injection, at the time of hypoglycemia, to correct it. Then a treatment to prevent the recurrence of hypoglycemia must be set, which may include frequent and glucose-enriched feeding, diazoxide and octreotide. When medical and dietary therapies are ineffective, or when a focal HI is suspected, surgical treatment is required. Focal HI may be definitively cured when the partial pancreatectomy removes the whole lesion. By contrast, the long-term outcome of diffuse HI after subtotal pancreatectomy is characterized by a high risk of diabetes, but the time of its onset is hardly predictable

Molecular Diagnosis of Neonatal Diabetes Mellitus Using Next-Generation Sequencing of the Whole Exome

Background: Accurate molecular diagnosis of monogenic non-autoimmune neonatal diabetes mellitus (NDM) is critical for patient care, as patients carrying a mutation in KCNJ11 or ABCC8 can be treated by oral sulfonylurea drugs instead of insulin therapy. This diagnosis is currently based on Sanger sequencing of at least 42 PCR fragments from the KCNJ11, ABCC8, and INS genes. Here, we assessed the feasibility of using the next-generation whole exome sequencing (WES) for the NDM molecular diagnosis. Methodology/Principal Findings: We carried out WES for a patient presenting with permanent NDM, for whom mutations in KCNJ11, ABCC8 and INS and abnormalities in chromosome 6q24 had been previously excluded. A solution hybridization selection was performed to generate WES in 76 bp paired-end reads, by using two channels of the sequencing instrument. WES quality was assessed using a high-resolution oligonucleotide whole-genome genotyping array. From our WES with high-quality reads, we identified a novel non-synonymous mutation in ABCC8 (c.1455G.C/p.Q485H), despite a previous negative sequencing of this gene. This mutation, confirmed by Sanger sequencing, was not present in 348 controls and in the patient’s mother, father and young brother, all of whom are normoglycemic. Conclusions/Significance: WES identified a novel de novo ABCC8 mutation in a NDM patient. Compared to the current Sanger protocol, WES is a comprehensive, cost-efficient and rapid method to identify mutations in NDM patients. W

EFL1 mutations impair eIF6 release to cause Shwachman-Diamond syndrome.

Shwachman-Diamond syndrome (SDS) is a recessive disorder typified by bone marrow failure and predisposition to hematological malignancies. SDS is predominantly caused by deficiency of the allosteric regulator Shwachman-Bodian-Diamond syndrome that cooperates with elongation factor-like GTPase 1 (EFL1) to catalyze release of the ribosome antiassociation factor eIF6 and activate translation. Here, we report biallelic mutations in EFL1 in 3 unrelated individuals with clinical features of SDS. Cellular defects in these individuals include impaired ribosomal subunit joining and attenuated global protein translation as a consequence of defective eIF6 eviction. In mice, Efl1 deficiency recapitulates key aspects of the SDS phenotype. By identifying biallelic EFL1 mutations in SDS, we define this leukemia predisposition disorder as a ribosomopathy that is caused by corruption of a fundamental, conserved mechanism, which licenses entry of the large ribosomal subunit into translation.Medical Research Council, Bloodwise, Wellcome Trust, Ted’s Gang, The Connor Wright Shwachman Diamond Projec

GSKIP (GSK3-beta interaction protein)

GSK3beta interaction protein (GSKIP) is a negative regulator of GSK3B (GSK3 beta) which is a highly conserved serine-threonine kinase involved in many cellular processes including glycogen metabolism, proliferation, differentiation, and development. GSKIP directly interacts with GSK3B through its C-terminal conserved GSK3B -binding domain (GID) and negatively regulates GSK3B in the Wnt/ beta -catenin signaling pathway. The overexpression of GSKIP may result in the activation of the Wnt pathway involved in hematopoietic stem cell homeostasis and normal megakaryopoiesis and in the development of leukemia stem cells in acute myeloid leukemia (AML). In a mouse model, GSK3B allelic deletion results in a myelodysplastic syndrome that, when combined with GSK3A deletion, leads to AML The germline duplication of ATG2B and GSKIP, both located in 14q32.2, predisposes to the development of familial myeloproliferative neoplasms with autosomal dominant inheritance, in particular essential thrombocythemia progressing to leukemia. Overexpression of ATG2B and GSKIP enhances megakaryocyte progenitor differentiation by increasing progenitor sensitivity to thrombopoietin. Both genes cooperate with somatic JAK2, MPL and CALR mutations and their overexpression provides a growth advantage to hematopoietic cells carrying these driver mutations that may explain the familial aggregation and the progression of essential thrombocythemia to myelofibrosis and leukemia

Granulopoïèse et leucémogenèse

Les neutropénies congénitales sont des maladies extrêmement rares, définies par une diminution permanente ou intermittente des neutrophiles circulants dans le sang. Les bases moléculaires de plusieurs de ces neutropénies ont récemment été déterminées, impliquant en particulier les gènes codant pour l’élastase neutrophile ELA2, le proto-oncogène GFI1, la protéine WASP et la protéine mitochondriale HAX1. Ces mutations, transmises selon un mode autosomique dominant (ELA2, GFI1), lié à l’X (WAS) ou autosomique récessif (HAX1) ont pour conséquence des modifications de la stabilité du contenu des granules - en particulier de l’élastase neutrophile -, des anomalies du cytosquelette et possiblement un excès d’apoptose. Les mutations ELA2 sont associées soit à une neutropénie profonde permanente, soit à une neutropénie intermittente, pseudo-sinusoïdale, suggérant que ces pathologies sont peut-être assez proches et que la variation temporelle des neutrophiles peut être modélisée par une fonction non linéaire. Les neutropénies congénitales, en particulier liées à ELA2, sont caractérisées par un risque leucémogène important (environ 15 % à 20 ans). Ce risque apparaît lié non pas à un effet oncogène des mutations, mais avant tout à la profondeur de la neutropénie, et par voie de conséquence à l’intensité du traitement par G-CSF qui est proposé à ces patients

Neonatal cholestatic jaundice as the first symptom of a mutation in the hepatocyte nuclear factor-1beta gene (HNF-1beta).

This report describes the phenotype of a novel de novo heterozygous frameshift mutation in the hepatocyte nuclear factor-1beta gene (HNF-1beta or TCF2) manifest as a neonatal paucity of intrahepatic bile ducts. HNF-1beta mutations should be considered in neonates with cholestatic jaundice associated with renal malformation or diabetes mellitus

Le MODY: modèle d’étude d’interactions génotype/phénotype dans le diabète de type 2

Le MODY (maturity onset diabetes of the young) est une forme de diabète familial, à transmission autosomique dominante et à début précoce, associé à des anomalies primaires de l’insulinosécrétion. Des mutations dans six gènes (l’enzyme glucokinase et cinq facteurs de transcription exprimés dans le pancréas) sont responsables de la plupart des cas de MODY. Cette hétérogénéité génétique est associée à une hétérogénéité métabolique et clinique faisant du MODY un modèle intéressant d’étude d’interactions génotype/phénotype dans le diabète.Maturity onset diabetes of the young (MODY) is a subtype of familial diabetes mellitus characterised by early onset, autosomal dominant inheritance and primary defects of insulin secretion. Mutations in six known genes (the enzyme glucokinase and five transcription factors expressed in pancreatic β-cells) cause most of the MODY cases. This genetic heterogeneity is associated with metabolic and clinical heterogeneity making MODY an interesting model of genotype/phenotype interaction in diabetes

Unsolved issues related to human mitochondrial diseases.

19 pagesInternational audience: Human mitochondrial diseases, defined as the diseases due to a mitochondrial oxidative phosphorylation defect, represent a large group of very diverse diseases with respect to phenotype and genetic causes. They present with many unsolved issues, the comprehensive analysis of which is beyond the scope of this review. We here essentially focus on the mechanisms underlying the diversity of targeted tissues, which is an important component of the large panel of these diseases phenotypic expression. The reproducibility of genotype/phenotype expression, the presence of modifying factors, and the potential causes for the restricted pattern of tissular expression are reviewed. Special emphasis is made on heteroplasmy, a specific feature of mitochondrial diseases, defined as the coexistence within the cell of mutant and wild type mitochondrial DNA molecules. Its existence permits unequal segregation during mitoses of the mitochondrial DNA populations and consequently heterogeneous tissue distribution of the mutation load. The observed tissue distributions of recurrent human mitochondrial DNA deleterious mutations are diverse but reproducible for a given mutation demonstrating that the segregation is not a random process. Its extent and mechanisms remain essentially unknown despite recent advances obtained in animal models