A novel missense mutation in MVK associated with MK deficiency and dyserythropoietic anemia

Production and stability of cultured red blood cells depends on the concentration of cholesterol in culture medium

The production of cultured red blood cells (cRBC) for transfusion purposes requires large scale cultures and downstream processes to purify enucleated cRBC. The membrane composition, and cholesterol content in particular, are important during proliferation of (pro)erythroblasts and for cRBC quality. Therefore, we tested the requirement for cholesterol in the culture medium during expansion and differentiation of erythroid cultures with respect to proliferation, enucleation and purification by filtration. The low cholesterol level (22 µg/dl) in serum free medium was sufficient to expand (pro)erythroblast cultures. Addition of 2.0 or 5.0 mg/dL of free cholesterol at the start of differentiation induction inhibited enucleation compared to the default condition containing 3.3 mg/dl total cholesterol derived from the addition of Omniplasma to serum free medium. Addition of 5.0 mg/dl cholesterol at day 5 of differentiation did not affect the enucleation process but significantly increased recovery of enucleated cRBC following filtration over leukodepletion filters. The addition of cholesterol at day 5 increased the osmotic resistance of cRBC. In conclusion, cholesterol supplementation after the onset of enucleation improved the robustness of cRBC and increased the yield of enucleated cRBC in the purification process.

Phosphomevalonate kinase deficiency expands the genetic spectrum of systemic autoinflammatory diseases

BACKGROUND

In the isoprenoid biosynthesis pathway, mevalonate is phosphorylated in 2 subsequent enzyme steps by MVK and PMVK to generate mevalonate pyrophosphate that is further metabolized to produce sterol and nonsterol isoprenoids. Biallelic pathogenic variants in MVK result in the autoinflammatory metabolic disorder MVK deficiency. So far, however, no patients with proven PMVK deficiency due to biallelic pathogenic variants in PMVK have been reported.

OBJECTIVES

This study reports the first patient with functionally confirmed PMVK deficiency, including the clinical, biochemical, and immunological consequences of a homozygous missense variant in PMVK.

METHODS

The investigators performed whole-exome sequencing and functional studies in cells from a patient who, on clinical and immunological evaluation, was suspected of an autoinflammatory disease.

RESULTS

The investigators identified a homozygous PMVK p.Val131Ala (NM_006556.4: c.392T>C) missense variant in the index patient. Pathogenicity was supported by genetic algorithms and modeling analysis and confirmed in patient cells that revealed markedly reduced PMVK enzyme activity due to a virtually complete absence of PMVK protein. Clinically, the patient showed various similarities as well as distinct features compared to patients with MVK deficiency and responded well to therapeutic IL-1 inhibition.

CONCLUSIONS

This study reported the first patient with proven PMVK deficiency due to a homozygous missense variant in PMVK, leading to an autoinflammatory disease. PMVK deficiency expands the genetic spectrum of systemic autoinflammatory diseases, characterized by recurrent fevers, arthritis, and cytopenia and thus should be included in the differential diagnosis and genetic testing for systemic autoinflammatory diseases.

The congenital dyserythropoieitic anemias: genetics and pathophysiology

PURPOSE OF REVIEW

The congenital dyserythropoietic anemias (CDA) are hereditary disorders characterized by ineffective erythropoiesis. This review evaluates newly developed CDA disease models, the latest advances in understanding the pathogenesis of the CDAs, and recently identified CDA genes.

RECENT FINDINGS

Mice exhibiting features of CDAI were recently generated, demonstrating that Codanin-1 (encoded by Cdan1) is essential for primitive erythropoiesis. Additionally, Codanin-1 was found to physically interact with CDIN1, suggesting that mutations in CDAN1 and CDIN1 result in CDAI via a common mechanism. Recent advances in CDAII (which results from SEC23B mutations) have also been made. SEC23B was found to functionally overlap with its paralogous protein, SEC23A, likely explaining the absence of CDAII in SEC23B-deficient mice. In contrast, mice with erythroid-specific deletion of 3 or 4 of the Sec23 alleles exhibited features of CDAII. Increased SEC23A expression rescued the CDAII erythroid defect, suggesting a novel therapeutic strategy for the disease. Additional recent advances included the identification of new CDA genes, RACGAP1 and VPS4A, in CDAIII and a syndromic CDA type, respectively.

SUMMARY

Establishing cellular and animal models of CDA is expected to result in improved understanding of the pathogenesis of these disorders, which may ultimately lead to the development of new therapies.

Fine-Tuning of Cholesterol Homeostasis Controls Erythroid Differentiation

Lipid metabolism is essential for stemness maintenance, self-renewal, and differentiation of stem cells, however, the regulatory function of cholesterol metabolism in erythroid differentiation is poorly studied. In the present study, a critical role for cholesterol homeostasis in terminal erythropoiesis is uncovered. The master transcriptional factor GATA1 binds to Sterol-regulatory element binding protein 2 (SREBP2) to downregulate cholesterol biosynthesis, leading to a gradual reduction in intracellular cholesterol levels. It is further shown that reduced cholesterol functions to block erythroid proliferation via the cholesterol/mTORC1/ribosome biogenesis axis, which coordinates cell cycle exit in the late stages of erythroid differentiation. The interaction of GATA1 and SREBP2 also provides a feedback loop for regulating globin expression through the transcriptional control of NFE2 by SREBP2. Importantly, it is shown that disrupting intracellular cholesterol hemostasis resulted in defect of terminal erythroid differentiation in vivo. These findings demonstrate that fine-tuning of cholesterol homeostasis emerges as a key mechanism for regulating erythropoiesis.

Congenital dyserythropoietic anemias

Congenital dyserythropoietic anemias (CDAs) are a heterogeneous group of inherited anemias that affect the normal differentiation-proliferation pathways of the erythroid lineage. They belong to the wide group of ineffective erythropoiesis conditions that mainly result in monolinear cytopenia. CDAs are classified into the 3 major types (I, II, III), plus the transcription factor-related CDAs, and the CDA variants, on the basis of the distinctive morphological, clinical, and genetic features. Next-generation sequencing has revolutionized the field of diagnosis of and research into CDAs, with reduced time to diagnosis, and ameliorated differential diagnosis in terms of identification of new causative/modifier genes and polygenic conditions. The main improvements regarding CDAs have been in the study of iron metabolism in CDAII. The erythroblast-derived hormone erythroferrone specifically inhibits hepcidin production, and its role in the mediation of hepatic iron overload has been dissected out. We discuss here the most recent advances in this field regarding the molecular genetics and pathogenic mechanisms of CDAs, through an analysis of the clinical and molecular classifications, and the complications and clinical management of patients. We summarize also the main cellular and animal models developed to date and the possible future therapies.

Gene Expression Analysis of Mevalonate Kinase Deficiency Affected Children Identifies Molecular Signatures Related to Hematopoiesis

Mevalonate kinase deficiency (MKD) is a rare autoinflammatory genetic disorder characterized by recurrent fever attacks and systemic inflammation with potentially severe complications. Although it is recognized that the lack of protein prenylation consequent to mevalonate pathway blockade drives IL1β hypersecretion, and hence autoinflammation, MKD pathogenesis and the molecular mechanisms underlaying most of its clinical manifestations are still largely unknown. In this study, we performed a comprehensive bioinformatic analysis of a microarray dataset of MKD patients, using gene ontology and Ingenuity Pathway Analysis (IPA) tools, in order to identify the most significant differentially expressed genes and infer their predicted relationships into biological processes, pathways, and networks. We found that hematopoiesis linked biological functions and pathways are predominant in the gene ontology of differentially expressed genes in MKD, in line with the observed clinical feature of anemia. We also provided novel information about the molecular mechanisms at the basis of the hematological abnormalities observed, that are linked to the chronic inflammation and to defective prenylation. Considering the broad and unspecific spectrum of MKD clinical manifestations and the difficulty in its diagnosis, a better understanding of MKD molecular bases could be translated to the clinical level to facilitate diagnosis, and improve management and therapy.

A Very Rare Congenital Dyserythropoietic Anemia Variant-Type IV in a Patient With a Novel Mutation in the KLF1 Gene: A Case Report and Review of the Literature

Congenital dyserythropoietic anemias comprise a group of very rare hereditary disorders characterized by ineffective erythropoiesis and distinct morphologic abnormalities of the erythroblasts in the bone marrow. The wide variety of phenotypes observed in these patients makes the diagnosis difficult; identification of the genetic variants is crucial in differential diagnosis and clinical management. We report the nineth case with congenital dyserythropoietic anemia type IV, with a novel mutation that has not been reported before.

Diagnosis and management of congenital dyserythropoietic anemias

Congenital dyserythropoietic anemias (CDAs) are inherited disorders hallmarked by chronic hyporegenerative anemia, relative reticulocytopenia, hemolytic component and iron overload. They represent a subtype of the inherited bone marrow failure syndromes, characterized by impaired differentiation and proliferation of the erythroid lineage. Three classical types were defined by marrow morphology, even if the most recent classification recognized six different genetic types. The pathomechanisms of CDAs are different, but all seem to involve the regulation of DNA replication and cell division. CDAs are often misdiagnosed, since either morphological abnormalities or clinical features can be commonly identified in other clinically-related anemias. However, differential diagnosis is essential for guiding both follow up and management of the patients.

Inborn errors of metabolism underlying primary immunodeficiencies

A number of inborn errors of metabolism (IEM) have been shown to result in predominantly immunologic phenotypes, manifesting in part as inborn errors of immunity. These phenotypes are mostly caused by defects that affect the (i) quality or quantity of essential structural building blocks (e.g., nucleic acids, and amino acids), (ii) cellular energy economy (e.g., glucose metabolism), (iii) post-translational protein modification (e.g., glycosylation) or (iv) mitochondrial function. Presenting as multisystemic defects, they also affect innate or adaptive immunity, or both, and display various types of immune dysregulation. Specific and potentially curative therapies are available for some of these diseases, whereas targeted treatments capable of inducing clinical remission are available for others. We will herein review the pathogenesis, diagnosis, and treatment of primary immunodeficiencies (PIDs) due to underlying metabolic disorders.

Monogenic autoinflammatory diseases

During the past 15 years, a growing number of monogenic inflammatory diseases have been described and their respective responsible genes identified. The proteins encoded by these genes are involved in the regulatory pathways of inflammation and are mostly expressed in cells of the innate immune system. Diagnosis remains clinical, with genetic confirmation where feasible. Although a group of patients exhibit episodic systemic inflammation (periodic fevers), these disorders are mediated by continuous overproduction and release of pro-inflammatory mediators, such as IL-1 and IL-6, and TNF and are best considered as autoinflammatory diseases rather than periodic fevers. Treatment with biologic agents that block these cytokines, particularly IL-1, has proved to be dramatically effective in some patients. Still, in many cases of autoinflammation no genetic abnormalities are detected and treatment remains suboptimal, raising the question of novel pathogenic mutations in unexplored genes and pathways.

Splicing mutation in MVK is a cause of porokeratosis of Mibelli

Porokeratosis is a chronic skin disorder characterized by the presence of patches with elevated, thick, keratotic borders, with histological cornoid lamella. Classic porokeratosis of Mibelli (PM) frequently appears in childhood with a risk of malignant transformation. Disseminated superficial actinic porokeratosis (DSAP) is the most common subtype of porokeratosis with genetic heterogeneities, and mevalonate kinase gene (MVK) mutations have been identified in minor portion of DSAP families of Chinese origin. To confirm the previous findings about MVK mutations in DSAP patients and test MVK's role(s) in PM development, we performed genomic sequence analysis for 3 DSAP families and 1 PM family of Chinese origin. We identified a splicing mutation of MVK gene, designated as c.1039+1G>A, in the PM family. No MVK mutations were found in three DSAP families. Sequence analysis for complementary DNA templates from PM lesions of all patients revealed a mutation at splice donor site of intron 10, designated as c.1039+1G>A, leading to the splicing defect and termination codon 52 amino acids after exon 10. Although no MVK mutations in DSAP patients were found as reported previously, we identified MVK simultaneously responsible for PM development.

Intermittent neutropenia as an early feature of mild mevalonate kinase deficiency

A 15-month-old boy, born to Iranian consanguineous parents presented with intermittent neutropenia interspersed with episodes of fever and leukocytosis since early infancy. No ELA2 mutations were found and the bone marrow study was normal. At age 4 years he progressed to more typical attacks of periodic attacks of fever, abdominal pain, oral aphthous ulcers, cutaneous rash and leukocytosis. The clinical and laboratory features were compatible with the mild form of mevalonate kinase deficiency, usually named "Hyper-IgD and periodic fever syndrome" (HIDS). Genomic sequencing of the mevalonate kinase (MVK) gene revealed homozygous missense mutation (p.Val377Ile). On demand dexamethasone resulted in a rapid amelioration of febrile episodes. The presentation of intermittent neutropenia has not been reported in HIDS and deserves more attention in large patient cohorts.

Congenital dyserythropoietic anemias: molecular insights and diagnostic approach

The congenital dyserythropoietic anemias (CDAs) are hereditary disorders characterized by distinct morphologic abnormalities of marrow erythroblasts. The unveiling of the genes mutated in the major CDA subgroups (I-CDAN1 and II-SEC23B) has now been completed with the recent identification of the CDA III gene (KIF23). KIF23 encodes mitotic kinesin-like protein 1, which plays a critical role in cytokinesis, whereas the cellular role of the proteins encoded by CDAN1 and SEC23B is still unknown. CDA variants with mutations in erythroid transcription factor genes (KLF1 and GATA-1) have been recently identified. Molecular diagnosis of CDA is now possible in most patients.

Clinical aspects and pathogenesis of congenital dyserythropoietic anemias: from morphology to molecular approach

Congenital dyserythropoietic anemias belong to a group of inherited conditions characterized by a maturation arrest during erythropoiesis with a reduced reticulocyte production in contrast with erythroid hyperplasia in bone marrow. The latter shows specific morphological abnormalities that allowed for a morphological classification of these conditions mainly represented by congenital dyserythropoietic anemias types I and II. The identification of their causative genes provided evidence that these conditions have different molecular mechanisms that induce abnormal cell maturation and division. Some altered proteins seem to be involved in the chromatin assembly, such as codanin-1 in congenital dyserythropoietic anemia I. The gene involved in congenital dyserythropoietic anemia II, the most frequent form, is SEC23B. This condition seems to belong to a group of diseases attributable to defects in the transport of newly synthesized proteins from endoplasmic reticulum to the Golgi. This review will analyze recent insights in congenital dyserythropoietic anemias types I and II. It will also attempt to clarify the relationship between mutations in causative genes and the clinical phenotype of these conditions.

Mevalonate kinase deficiency, a metabolic autoinflammatory disease

Mevalonate kinase deficiency is a rare autosomal recessive inborn error of metabolism with an autoinflammatory phenotype. In this review we discuss its pathogenesis, clinical presentation and treatment. Mutations in both copies of the MVK-gene lead to a block in the mevalonate pathway. Interleukin-1beta mediates the inflammatory phenotype. Shortage of a non-sterol isoprenoid product of the mevalonate pathway, Geranylgeranylpyrophosphate leads to aberrant activation of the small GTPase Rac1, and inflammasome activation. The clinical phenotype ranges widely, depending on the severity of the enzyme defect. All patients show recurrent fevers, lymphadenopathy and high acute phase proteins. Severely affected patients have antenatal disease onset, dysmorphic features, growth retardation, cognitive impairment and progressive ataxia. Diagnosis relies on mutation analysis of the MVK-gene. There is no evidence based therapy. IL-1 blockade is usually effective. Severe cases require allogeneic stem cell transplantation. Targeted therapies are needed.

Congenital dyserythropoietic anemias

PURPOSE OF REVIEW

Congenital dyserythropoietic anemias (CDAs) are rare hereditary disorders characterized by ineffective erythropoiesis and by distinct morphological abnormalities of erythroblasts in the bone marrow. Characteristic morphological aberrations were the cornerstone of diagnosis, but following the identification of several causative genes, the molecular approach could represent a rapid tool for the identification of these conditions. This review presents advances in diagnosis and classification of CDAs.

RECENT FINDINGS

The classification of CDAs has long been based on morphological features. Now, the discovery of some of the responsible genes allows reconsideration of part of the classification. The first CDA partly accounted for genetically has been CDA 1, through the discovery in 2002 of the gene responsible, CDAN1, encoding codanin-1. Recently, the dramatic identification of the genes responsible for CDA II, SEC23B, and for a hitherto unnamed CDA, KLF1, took place. SEC23B encodes SEC23B which is a component of the coated vesicles transiting from the endoplasmic reticulum to the cis compartment of the Golgi apparatus. A unique mutation in KLF1, which encodes the erythroid transcription factor KLF1, causes major ultrastructural abnormalities, the persistence of embryonic and fetal hemoglobins, and the absence of some red cell membrane proteins.

SUMMARY

Studies of genotype-phenotype relationship, as has already been done for CDA II, will allow a more accurate prognosis. Identification of the responsible genes has opened new vistas for research on CDAs.

Perinatal onset mevalonate kinase deficiency

Defects in mevalonate kinase, a critical rate-limiting enzyme in cholesterol and isoprene metabolism, have been associated with 2 clinical phenotypes: mevalonic aciduria, which presents in infancy or early childhood with growth failure, dysmorphic features, and neurologic disease; and hyperimmunoglobulinemia D and periodic fever syndrome, which usually presents outside the neonatal period as an autoinflammatory periodic fever syndrome. This report describes a kindred with 2 siblings affected by severe mevalonate kinase deficiency (mevalonic aciduria) with perinatal onset. Dysmorphic and central nervous system abnormalities, anemia, and cholestasis were prominent features in 1 sibling. Both cases were fatal, 1 in the immediate neonatal period and 1 in utero. The small number of cases of mevalonate kinase deficiency presenting in the perinatal period have typically been severely affected, with signs and symptoms of a severe multisystem disorder. Predominant features of perinatal onset mevalonate kinase deficiency include intrauterine growth restriction, cerebral ventriculomegaly, dysmorphic features, skeletal abnormalities, dyserythropoietic anemia with extramedullary erythropoiesis, thrombocytopenia, cholestatic liver disease, persistent diarrhea, renal failure, recurrent sepsis-like episodes, and failure to thrive. Clinical findings may mimic severe intrauterine viral infection, a chromosomal abnormality, or an acute sepsis syndrome, potentially contributing to delays in diagnosis of this rare condition. Perinatal onset mevalonate kinase deficiency is associated with a very poor prognosis, with death in utero or in early infancy. Detailed autopsy findings in mevalonate kinase deficiency have rarely been reported.