Congenital Red Blood Cell Disorders

The integrity and function of red blood cells (RBCs) are vital to neonatal health because RBCs enable the delivery of oxygen to tissues, and therefore support the aerobic metabolism of all organ systems of the newborn. Furthermore, anemia is the most common hematological abnormality in the NICU.1

Premature infants in particular are at high risk of developing anemia for several reasons, including anemia of prematurity, iatrogenic blood loss, suboptimal nutrition, and losses associated with clinical decompensation such as sepsis.2 Anemia in the newborn is defined such as a hemoglobin value or hematocrit concentration greater than 2 deviations below the normal mean for postnatal age.

While physiological anemia of the newborn and anemia of prematurity are the most common causes of neonatal anemia, neonatologists should remain alert to additional causes of anemia and other RBC disorders caused by associated comorbidities and optimize their treatment.3 It is prudent to NICU physicians become familiar with fetal hematopoiesis and its regulation, as well as inherited RBC disorders.

Conceptually, anemia can be divided into instances of inadequate GR production, increased GR destruction, or whole blood loss (the latter etiology being outside the scope of this article).

Anemia secondary to suboptimal GR production is often due to congenital genetic disorders. This alteration may occur in the progenitor cells that cause pancytopenia (e.g., Fanconi anemia [FA], Shwachman-Diamond syndrome (SSD), radium-absent thrombocytopenia syndrome [TAR]), or in the specific cell line of pancytopenia. erythrocytes (e.g., Diamond-Blackfan anemia [DBA]).

Abnormal red blood cell structure ( e.g., hereditary spherocytosis [EsH], hereditary elliptocytosis [ElH], sickle cell anemia) or abnormal enzyme function (e.g., glucose-6-phosphate dehydrogenase [G6PD] deficiency, of pyruvate kinase [PK]) result in anemia due to malformed or poorly adapted RBCs that are more rapidly cleared from the circulation. Variations in the underlying etiology of altered RBC function have different associated pathologies as well as treatment prognoses.

The objective of this article is to review normal neonatal erythropoiesis and its genetic regulation, highlight key features of the underlying genetic etiologies, summarize the approach to the diagnosis of inherited GR disorders, and outline appropriate steps for management.

Erythropoiesis is the process by which red blood cells or erythrocytes are formed.

The sites of erythropoiesis vary throughout gestation, beginning in the yolk sac (3 to 8 weeks of gestation) and then moving to the liver (6 to 30 weeks of gestation) and spleen (9 to 28 weeks of gestation). At 28 weeks of gestation, the bone marrow becomes the primary site of erythropoiesis.4

GR formation in the early embryo begins with the mesodermal cells of the yolk sac and is known as primitive erythropoiesis. All subsequent RBC formation begins with hematopoietic stem cells and is known as definitive erythropoiesis. Hematopoietic stem cells differentiate into erythrocytes in multiple stages.

Mature erythrocytes do not contain nuclei or organelles, so hemoglobin synthesis occurs in precursor cells. The maturation of erythrocyte precursors involves proliferation through cell division, increased hemoglobin synthesis, decreased cell size, degeneration of nuclei, and decreased cytoplasmic RNA.5

> Hemoglobin synthesis

Hemoglobin is a tetramer composed of 4 globin chains, each containing a heme molecule.

Each heme molecule is a ring of protoporphyrin with iron (Fe2+) in the center, which facilitates the reversible binding of oxygen.6 There are 6 types of globin chains. The genes encoding α-globin (HBA1, HBA2) and ƺ-globin (HBZ) are located on chromosome 16. The genes encoding β-globin (HBB), γ-globin (HBG1, HBG2), δ- globin (HBD) and Ԑ-globin (HBE1) are located on chromosome 11. The expression of these genes varies during embryonic and fetal development and give rise to different types of hemoglobin, in a process known as hemoglobin switch. HbF is the primary fetal hemoglobin. At the end of fetal gestation, HbF production decreases and HbA production begins. HbA becomes the dominant hemoglobin 6 months after birth.7

> Regulation of erythropoiesis

Erythropoietin (EPO) is a hormone produced by the kidney that acts on the bone marrow to positively regulate erythropoiesis.

Hypoxia causes increased production of EPO . EPO binds to its receptor, EPOR, leading to a cascade of events that allows the early release of reticulocytes from the bone marrow, decreases the time required for RBC maturation, and prevents erythrocyte death. Many transcription factors play a key role in regulating erythropoiesis. Some of these include GATA1, LDB1, FOG1, SCL/TAL1 and LMO2.5,8

Congenital red blood cell disorders can be divided into bone marrow failure syndromes, hemoglobinopathies, sideroblastic anemia, RBC membrane defects, and RBC enzyme defects.

> Bone marrow failure syndromes

Bone marrow failure syndromes are disorders that lead to decreased production of one or more cell lines.

All of the disorders discussed here involve reduced red blood cell production, manifesting as anemia. These syndromes increase the predisposition to developing malignant tumors later in life, so early diagnosis is key to ensuring adequate surveillance of affected people.

Fanconi anemia

Fanconi anemia (FA) (Online Mendelian Inheritance in Man [OMIM]: 227650, 300514, 227645, 614082, 617244 and others) is a disorder of chromosomal instability. About one-third of FA patients do not show phenotypic features, which can present a diagnostic challenge. In patients who have clinical features, the expression may be variable. Abnormalities may include intrauterine growth restriction, skeletal anomalies (e.g., thumb malformations, scoliosis), skin depigmentation, genitourinary anomalies, heart defects, intestinal atresia, microcephaly, and hydrocephalus.9

Mutations occur in 1 of 21 genes, including FANCA (the most common), FANCC, and FANCG. Inheritance is autosomal recessive, except for FANCB (which is X-linked recessive) and FANCR (which is autosomal dominant). The mechanism by which AF gene mutations cause disease is still being investigated.10

Laboratory findings include pancytopenia, reticulocytopenia, hypocellular bone marrow, and occasionally elevated hemoglobin (Hb)F. The diagnosis of FA is made by chromosome breakage analysis, which demonstrates increased DNA damage in the presence of cross-reactive agents. Many patients with FA develop malignant tumors in the first 3 decades of life, and most present with bone marrow failure by 40 years of age. Supportive treatment includes transfusions, granulocyte colony-stimulating factor (G-CSF), and granulocyte-macrophage colony-stimulating factor. Curative treatment is with hematopoietic stem cell transplantation.11

Diamond-Blackfan anemia

Diamond-Blackfan anemia ( DBA) (OMIM: 105650, 612562, 613309, and others) is a pure RBC aplasia characterized by a decrease in erythrocyte precursors with remaining normal values ​​in the bone marrow. About 50% of patients have craniofacial anomalies (eg, cleft lip and palate), thumb anomalies, and heart defects.12 ADB is caused by mutations in genes that encode ribosomal proteins.

At least 17 genes are involved, including RPS19 (the most common), RPL11 and RPS26. Inheritance is mainly autosomal dominant and rarely X-linked recessive. Laboratory findings include macrocytic anemia and reticulocytopenia. Bone marrow evaluation can differentiate ADB from other bone marrow failure syndromes due to normal numbers of myeloid cells (white blood cell precursors) and megakaryocytes (platelet precursors). Its management involves transfusions of RBCs and corticosteroids. Bone marrow transplant is curative and can improve outcomes.11

Shwachman-Diamond syndrome

Shwachman-Diamond syndrome ( SDS) (OMIM: 260400, 617941) is a rare congenital disorder described by Shwachman et al. in 1964 as syndrome of pancreatic insufficiency and bone marrow dysfunction.13 This disorder is characterized by its genetic heterogeneity with 2 main forms currently distinguished.14,15 SDS is characterized by multiorgan and systemic involvement, the predominant manifestations being exocrine pancreatic insufficiency. , skeletal abnormalities, and bone marrow failure.16

Other manifestations of SDS include skeletal abnormalities such as thoracic dystrophy, neurocognitive problems, and hepatomegaly.17 Although neutropenia is the most common hematologic abnormality in SDS, aplastic anemia and macrocytosis may be among the symptoms present as well.18,19 SDS It rarely occurs in newborns. In those rare cases, typical neonatal manifestations include acute severe infections, aplastic anemia, and growth retardation secondary to exocrine pancreatic insufficiency.18,20,21 Fecal fat levels may increase due to malabsorption. Decreases in other serum biomarkers such as trypsinogen and isoamylase can be seen later in life.22

SDS-specific growth charts have been developed for affected patients.23 Anemia in SDS can range from intermittent or clinically asymptomatic to severe, requiring RBC transfusion. Patients with SDS have a lifelong risk of malignant transformation, typically myelodysplasia or acute myeloid leukemia.18 Diagnosis is made based on the presence of clinical features and can be confirmed by comprehensive genomic or gene-targeted testing.17 18

Management includes G-CSF for neutropenia, RBC transfusion for anemia, and pancreatic enzyme replacement.11 Hematopoietic stem cell transplantation is the only treatment for severe pancytopenia, myelodysplastic syndrome, or leukemic transformation.16

Radium-absent thrombocytopenia (TAR) syndrome

Thrombocytopenia with absence of rays (TAR) syndrome ( OMIM: 274000) is a rare genetic disorder characterized, as its name indicates, by a reduced platelet count and the absence of rays.24 The disease is inherited autosomal recessive and is caused by compound heterozygosity by a rare null mutation in the RBM8A gene on chromosome 1, region q21.25 Aplastic anemia is a possible manifestation of the erythroid lineage in TAR syndrome; however, it does not occur frequently in newborns. The presence of thumbs helps differentiate TAR syndrome from AF.26

Dyskeratosis congenita

Dyskeratosis congenita (DC; OMIM: 127550, 613989, 613990, 615190, 616553, 613987, 224230, 616353, 613988, 305000) is a rare disorder characterized by mucocutaneous abnormalities and pancytopenia due to bone marrow failure. The classic triad seen is abnormal skin pigmentation, dystrophic nails, and oral leukoplakia.27 Patients with CD have mutations in one of several genes. Inheritance is X-linked recessive (DKC1 gene), autosomal dominant (TERC, TERT, or TINF2 genes), or autosomal recessive (TERT, RTEL1, ACD, NHP2, NOP10, PARN, or WRAP53 genes). These mutations involve the telomerase complex, which is required for the synthesis and maintenance of telomere repeats at the ends of chromosomes to ensure cell survival. Laboratory findings include pancytopenia, reticulocytopenia, macrocytosis, and occasionally increased HbF.

Diagnosis can be made with genetic testing for known mutations or flow cytometry, fluorescence, and in situ hybridization of white blood cell subsets, which will show shortened telomeres. Most patients with CD die due to complications from bone marrow failure. Hematopoietic stem cell transplantation is not necessarily curative given the high risk of fatal pulmonary fibrosis and vascular complications.11

> Hemoglobinopathies

Hemoglobinopathies are caused by mutations in genes involved in hemoglobin synthesis.

They are divided into 2 main groups: thalassemic syndromes and abnormal hemoglobins (also known as structural hemoglobin variants). In thalassemic syndromes, mutations lead to a decreased rate of hemoglobin synthesis, but the structure of hemoglobin is normal. In abnormal hemoglobins, mutations cause changes in the hemoglobin structure.

> Thalassemias

Thalassemias are caused by decreased or absent synthesis of globin chains and are named according to the type of chain that is affected.

Disruption of globin chain synthesis leads to reduced hemoglobin synthesis. Unaffected globins are synthesized at a normal rate and the imbalance between α and β chains can cause damage to erythrocyte precursors. The details of α and β thalassemia are discussed below. Screening tests for thalassemia include a complete blood count, peripheral blood smear, and iron studies (to rule out iron deficiency anemia). Hemoglobin electrophoresis can also be performed. The definitive diagnosis can be made with genetic tests.27

β-Thalassemia. In β-thalassemia (OMIM: 613985), excess α chains precipitate and form inclusion bodies. This leads to oxidative stress, damage to cell membranes, and eventually apoptosis of erythrocyte precursors. The death of these precursors is called ineffective erythropoiesis. The bone marrow attempts to increase RBC production, but the RBCs that are created contain inclusion bodies and are sequestered and destroyed by the spleen.

Patients with β-thalassemia may be asymptomatic in the fetal period and up to 6 months after birth due to the predominance of HbF (α2-γ2). Around 6 months of age, γ-globin production decreases and the inability to synthesize β-globin due to mutations leads to symptoms of anemia. γ and δ globins are upregulated, but this is not sufficient to compensate for HbA (α2-β2) deficiency. Anemia causes an increase in EPO and the resulting ineffective erythropoiesis leading to bone marrow expansion, thinning of the bone cortex, frontal pons, and extramedullary hematopoiesis.

β-thalassemia is inherited in an autosomal recessive manner. Nearly 300 mutations have been discovered in the β-globin gene and additional mutations in the δ and γ globin genes.

The following conventions are used to describe β-thalassemia genes: β+ (decreased globin production), β0 (no globin production), and β (normal globin production). β-Thalassemia can be classified using 2 different classification systems. The first system takes into consideration the severity of the phenotype based on the amount of functional β-globins.28,29 The second classification system is based on transfusion requirements: transfusion-dependent thalassemia and non-transfusion-dependent thalassemia.

Patients requiring long-term transfusions are at risk of iron overload. Iron accumulation leads to deposition in the liver, heart and pancreas, causing organ damage. Patients must undergo iron chelation therapy in addition to receiving transfusions. Deferoxamine is the most commonly used agent. Hematopoietic stem cell transplantation can cure thalassemia major.28

α-Thalassemia. In α-thalassemia (OMIM: 604131), the inability to synthesize α-globin can cause effects in the uterus because the primary type of intrauterine hemoglobin is HbF (α2-γ2). The accumulation of γ-globins does not lead to precipitation. In fact, γ-globins can form tetramers called Hb Bart (γ4). As β-globins are produced later in gestation, they can also form tetramers called HbH (β4). HbH can eventually precipitate and form inclusion bodies, leading to the destruction of red blood cells. Hb Bart and HbH have a high affinity for oxygen and therefore lead to a decrease in oxygen delivery to the tissues.28

There are several forms of α-thalassemia. α-Thalassemia minor (trait) results from 2 dysfunctional genes and causes mild anemia. α-Thalassemia intermedia, also known as HbH disease, results from 2 dysfunctional genes with diminished function. HbH disease generally does not require transfusions, except in cases of hemolytic crisis. The most severe form of α-thalassemia occurs when α-globins are not produced and is called hydrops fetalis syndrome by Hb Bart. Only fetuses with Hb Bart develop hypoxia, heart failure, and hydrops fetalis; those who survive to birth often require long-term transfusions.28,30

> Abnormal hemoglobins

Abnormal hemoglobins, or structural hemoglobin variants, are caused by mutations that lead to changes in the structure of hemoglobin.

Mutations are inherited in an autosomal co-dominant manner. This group of disorders can be divided into 4 categories: (1) sickle cell disorders, (2) hemoglobins with decreased stability (e.g., Brockton, Philadelphia, and Peterborough variants leading to hemolytic anemia; Hirosaki and Terre Haute variants causing hemolytic anemia and Heinz body formation), (3) hemoglobins with altered affinity for oxygen (e.g., high-affinity variants Kempsey, Hiroshima, York; low-affinity variants Kansas, Beth Israel, St. Mandé), and ( 4) hemoglobins that cause methemoglobinemia (e.g., M-Iwate, M-Saskatoon variants).31,32 This review discusses sickle cell disorders, the most common category of abnormal hemoglobins.

Sickle cell anemia (sickle cell disease). Sickle cell disease (AD; OMIM: 603903) is a group of disorders characterized by the production of HbS, the formation of sickle cells, and their effects on various organs. HbS occurs due to a mutation in the HBB β-globin gene on chromosome 11p15.4. The mutation leads to a substitution of glutamic acid for valine at amino acid 6. Inheritance is autosomal recessive.33 Patients who are homozygous for HbS (SS) have the most severe disease phenotype. Heterozygous patients, with 1 HbS allele in combination with another β-globin mutation (such as HbC or β-thalassemia) have less severe manifestations of the disease.

When HbS is deoxygenated, a hydrophobic area of ​​the hemoglobin chain is exposed. Other HbS molecules bind together to hide the hydrophobic areas, thus creating HbS polymers. As these polymers elongate, they distort the RBC membrane, giving it a sickle shape. Sickle cells cannot change shape and therefore increase blood viscosity and clog capillaries.34 Polymerization and sickling may be reversible with HbS reoxygenation. This cyclic activity can damage RBC membranes and cause chronic hemolytic anemia.31

The classic presentation of AD is vaso-occlusive crisis, which occurs most frequently in bones, lungs, liver, spleen, eyes, central nervous system, and urogenital tract. It can be caused by acidosis, hypoxia, dehydration, infection, fever, and cold temperatures. Babies may have pain and edema in their hands and feet, known as hand-foot syndrome. Trapping of blood in the spleen can lead to splenic sequestration and loss of splenic function over time.35 This predisposes to infections with encapsulated organisms, such as Pneumococcus , Haemophilus, and Salmonella.36

Infections are the most common cause of death in AD, especially in the first years of life. Patients may also develop acute chest syndrome, defined by fever or respiratory symptoms along with pulmonary infiltrates seen on chest x-ray. Other serious complications of AD include fat embolisms due to bone marrow necrosis, pulmonary hypertension, aplastic episodes (especially with parvovirus infection), cardiomegaly, avascular necrosis of the hip, retinopathy, and stroke.

Findings of AD on laboratory evaluation include normocytic anemia, poikilocytosis, anisocytosis (with sickle cells, target cells, nucleated erythrocytes, and Howell-Jolly bodies), and reticulocytosis.35 Sickle cell anemia occurs infrequently in the neonates; This is largely because HbF cannot copolymerize with HbS.37

Early detection and diagnosis of AD is essential for disease recognition and immediate intervention, as sickle cell events and complications can begin as early as 3 months of age. It is important to highlight the fact that the initial presentation could be a fatal infection or an acute splenic sequestration crisis.38

In the United States, all newborns have been screened for AD since 2006.39 Three different technologies, high-performance liquid chromatography, isoelectric focusing, and capillary electrophoresis, can be used to separate and quantify hemoglobin types from samples of dried blood or umbilical cord blood. Neonate samples contain mainly HbF and some HbA. Identification of HbS in the sample suggests AD and can be confirmed with other testing modalities.40

Treatment of AD includes measures to prevent vaso-occlusive crises, such as hydration and avoiding low-oxygen situations (e.g., high altitude and strenuous exercise).

Hydroxyurea can increase HbF production and decrease the number of vaso-occlusive crises. During a vaso-occlusive crisis, analgesia is the mainstay of therapy. RBC transfusion can decrease the number of circulating sickle cells and improve blood flow. Isolated transfusions are performed in cases of splenic sequestration, aplastic crisis, and acute chest syndrome. Patients at high risk for or history of stroke are treated with long-term transfusions. Patients requiring long-term transfusions need iron chelation therapy to prevent iron overload. Antibiotic prophylaxis with penicillin and early initiation of antibiotics in cases of suspected infection are crucial. Hematopoietic stem cell transplantation is the only curative therapy, but its use is limited by the difficulty of finding HLA-compatible family donors.35,36,38

Sickle cell trait. Heterozygous patients with one HbS allele and one normal α-globin allele have sickle cell trait. These patients are usually asymptomatic, but may have mild symptoms during times of extreme exertion.35 Sickle cell trait provides protection against severe Plasmodium falciparum malaria . This explains why the HbS allele has a high prevalence in sub-Saharan Africa, the Mediterranean, the Middle East and India.38

> Sideroblastic anemia

Sideroblastic anemia refers to a subset of inherited and acquired bone marrow disorders in which iron accumulates in excess in the mitochondria of erythrocyte precursors. The pathophysiological impact of this defect is the abnormal metabolism of iron by the mitochondria. Ultimately, this results in a large increase in reactive oxygen species that cause cellular damage and eventual cell death.41

X-linked sideroblastic anemia. X-linked sideroblastic anemia (ASLX; OMIM: 300751) is an to the X of chromosome presence of pyridoxal phosphate as a cofactor.44 This enzymatic defect results in inefficient heme synthesis, which in turn leads to ineffective erythropoiesis and systemic iron overload.43

Clinical features include anemia, formation of ring sideroblasts (erythroid precursors with a perinuclear ring formed by iron-laden mitochondria) in the bone marrow, and systemic iron overload.45 Anemia in ASLX is highly variable and typically microcytic and hypochromic, with increasing GR distribution width. Occasionally, prominent erythrocyte dysmorphism (micro-, normo-, and even macrocytic) has been observed.46 Like most X-linked recessive diseases, most heterozygous women do not show symptoms.

However, occasionally heterozygous females may be affected due to skewed lyonization or severe loss-of-function mutations in the ALAS2 gene that result in apoptosis of mutated erythroid precursors.47 Management includes high-dose pyridoxine supplementation and reduction therapies. of iron. Pyridoxine (vitamin B6), which becomes the cofactor of ALAS2 pyridoxal phosphate, acts to prolong the half-life of ALAS2. However, the answer is variable.48

The primary goal of iron-reducing therapies, such as phlebotomy and iron chelation, is to prevent the development of liver cirrhosis, hepatocellular carcinoma, diabetes, and heart failure due to iron overload.43

Pearson syndrome. Pearson marrow-pancreas syndrome (OMIM: 557000) is a rare mitochondrial disorder first described by Howard Pearson and colleagues in 1979.49 To date, only approximately 150 cases have been reported.50 This syndrome results from sporadic deletions of the mitochondrial genes ND4, ND5, ND6 and CYTB. These genes encode the subunits of nicotinamide adenine dinucleotide (NADH) dehydrogenase and cytochrome b, the inner mitochondrial membrane proteins that are part of the electron transport chain.51,52

Mutations in these genes cause impaired oxidative phosphorylation, leading to deficiency in adenosine triphosphate (ATP) production, which in turn leads to increased anaerobic glycolysis and lactic acidosis. Clinical features include macrocytic anemia and exocrine pancreatic insufficiency, as well as hepatic and renal failure.50 Anemia is the most prominent clinical feature and is typically areregenerative, with low reticulocyte count and refractory in nature, requiring frequent blood transfusions.49, 53

Bone marrow features suggestive of Pearson syndrome include hypocellularity and the presence of cytoplasmic vacuolization of myeloid and erythroid precursors, as well as ringed sideroblasts.54,55 Other hematologic findings include neutropenia and thrombocytopenia.50 Exocrine pancreatic insufficiency is caused by fibrosis. and can cause malabsorption and growth retardation.53

In addition to lactic acidosis, other biochemical abnormalities that may occur in patients with Pearson syndrome are elevated plasma alanine and decreased plasma levels of citrulline and arginine. The latter is thought to be due to a decrease in ornithine transcarbamylase activity.56 Management is supportive with blood transfusions and G-CSF, and correction of metabolic acidosis.50 The prognosis is poor and children often die. in infancy or early childhood.57

The causes of death are usually multiorgan failure, persistent metabolic acidosis, and septicemia.58 Bone marrow dysfunction resolves in survivors, but they develop Kearns-Sayre syndrome characterized by external ophthalmoplegia, retinitis pigmentosa, and cardiac conduction abnormalities.53 ,59,60,61

> Red blood cell membrane defects

The erythrocyte membrane requires a unique composition of lipids and proteins to achieve a flexible biconcave shape, allowing these cells to withstand the stress of transport through the circulatory system. Abnormalities in any of these key components can lead to malformations, resulting in membrane instability and increased erythrocyte lysis.

hereditary spherocytosis

Hereditary spherocytosis (EsH) (OMIM 182900, 616649, 270970, 612653, 612690) constitutes a heterogeneous group of congenital red blood cell disorders described by Oskar Minkowski in 1900.62 These disorders arise from alterations in the genes ANK1, SPTB, SPTA1, SLC4A1 and

EBB42, which encode the red blood cell membrane proteins ankyrin, β-spectrin, α-spectrin, band 3, and protein 4.2, respectively.63 Defects in α-spectrin have been reported to cause severe anemia, while Defects in ankyrin, band 3, and protein 4.2 have been associated with the development of mild to moderate anemia.64 The altered structure of membrane proteins leads to an imperfect connection of the inner membrane cytoskeleton to the outer lipid bilayer.65 As As a result, erythrocytes lose their ability to maintain the distinctive biconcave shape and assume a spherical shape instead.66

Other characteristics of spherocytes include decreased mean corpuscular volume, increased mean corpuscular hemoglobin concentration, absence of pale central region, and increased osmotic fragility. Tests that measure hemolysis (osmotic fragility test, acidified glycerol test, and Pink test) can be used as first-line diagnostic means; however, the sensitivity of these tests is low.65

The eosin-5’-maleimide (EMA) flow cytometry test has been used as an alternative test for the diagnosis of EsH with high sensitivity and specificity. This test is based on labeling RBCs with the fluorescent dye EMA. Spherocytes have decreased dye binding compared to normal RBCs and therefore fluorescence intensity decreases.65,67

Typical clinical manifestations of SpH include anemia with hemolysis, reticulocytosis, jaundice due to unconjugated hyperbilirubinemia, cholelithiasis, and splenomegaly.64 The most common presenting sign in newborns with SpH is jaundice. Anemia is present in less than half of newborns affected by EsH while splenomegaly is rarely detected.

Management includes control of hyperbilirubinemia with phototherapy and exchange transfusion, if necessary. Clinically significant anemia may benefit from transfusions of RBC concentrates.68 The use of recombinant EPO has been reported with variable success.69,70,71 Folic acid should be administered to patients with moderate or severe disease. Splenectomy is performed very infrequently during the first year of life.68

hereditary elliptocytosis

Hereditary elliptocytosis (ElH) (OMIM 611804, 130600, 617948, 166900) comprises a heterogeneous group of congenital RBC disorders characterized by elongated, oval, or elliptical erythrocytes. These conditions are caused by alterations in the genes EPB41, SPTA1, SPTB, and SLC4A1. These genes encode proteins 4.1, α-spectrin, β-spectrin, and band 3, respectively. Another form of ElH is called hereditary pyropoikilocytosis (PPH; OMIM 266140) and is caused by a defect in the SPTA1 gene, which encodes the protein spectrin.72,73,74,75,76

As can be seen, the genes and proteins affected in ElH overlap with those affected in SpH. As such, the 2 groups of disorders share many clinical features. The hallmark of elliptocytosis is the presence of oval or elliptical-shaped RBCs in the peripheral blood smear.77

Newborns usually present with transient hemolytic anemia and jaundice. RBC transfusion and phototherapy may be indicated in cases of severe anemia and hyperbilirubinemia.78 PPH is the most severe form of ElH. It typically occurs in neonates with severe hemolytic anemia that persists throughout life.79 Complications from hemolysis, such as splenomegaly and cholelithiasis, are common and may require splenectomy.80,81

> Enzymatic defects in red blood cells

Although erythrocytes lack a nucleus and other organelles, the rich enzymatic composition is vital for their proper functioning. The primary form of metabolism in the erythrocyte is the Embden-Meyerhof pathway, which requires a functional pyruvate kinase (PK) for the cell to generate stored energy as ATP, glutathione, and pyridine nucleotides (NADH and nicotinamide adenine dinucleotide phosphate [NADPH). ]). Next, most of the NADPH in RBCs is formed through glucose-6-phosphate metabolism, enabled by G6PD. Both metabolic processes must be intact for adequate cellular energy formation. NADPH formation also maintains adequate levels of reduced glutathione, which protects against oxidative damage.82

G6PD deficiency

G6PD deficiency (OMIM: 300908) was first described by Alving et al. in 1956 in patients who had primaquine-induced hemolytic anemia.83 The disorder has an X-linked dominant inheritance and is caused by mutations in the G6PD gene located in the q28 region of the X chromosome.84

G6PD is an internal enzyme that is present in all cells of the human body. It participates in the pentose phosphate pathway and plays a key role in defending against cellular damage due to oxidative stress. The reduced NADPH generated in the pentose phosphate pathway is then used to convert oxidized glutathione to its reduced state.85 RBCs are particularly vulnerable to reactive oxidation due to their exposure to large amounts of oxygen, as well as their inability to synthesize new proteins like mature cells.86 G6PD deficiency leads to a state of NADPH deficiency, inability to reduce oxidized glutathione, and consequently to severe oxidative damage.

Hemolytic anemia follows as a result.87 Hemolysis can be caused by stress, certain foods rich in oxidizing substances (e.g., fava beans), and medications (e.g., quinine, sulfas), as well as certain environmental exposures (e.g., naphthalene of mothballs).88.89

In neonates, G6PD deficiency poses a risk of developing indirect hyperbilirubinemia and the need for phototherapy. Liu et al. reported that in neonates with G6PD deficiency the risk of hyperbilirubinemia is 3.92 times higher and the risk of phototherapy is 3.01 times higher compared to neonates with normal G6PD.90 G6PD deficiency also increases the risk of kernicterus. Thus, 20.8% of infants included in the kernicterus registry had G6PD deficiency compared to the overall prevalence of G6PD deficiency in the United States of 4% to 7%.91,92

Diagnosis can be made with quantitative spectrophotometric analysis or a rapid fluorescent spot test that detects the generation of NADPH from NADP. During the period of acute hemolysis, G6PD deficiency test results may be falsely negative due to preferential lysis of older cells with lower levels of G6PD. Newborns are not routinely screened for G6PD deficiency in the United States.

The cornerstone of G6PD deficiency management is the avoidance of oxidative stressors.93 In neonates, it is important to control jaundice and prevent kernicterus through phototherapy and, in severe cases, exchange transfusion.93,94,95

Pyruvate kinase deficiency

Pyruvate kinase (PK) deficiency (OMIM: 266200) is an inherited metabolic disorder first reported by Valentine et al. in 1961.96 This disorder has autosomal recessive inheritance and is caused by a homozygous or compound heterozygous mutation in the PKLR gene on chromosome 1, region q22.97 PK catalyzes the last step of glycolysis: the conversion of phosphoenolpyruvate to pyruvate with a yield of ATP.

The decrease in ATP production creates a deficit in the energy necessary to maintain structural and functional cellular integrity with subsequent premature destruction of cells in the spleen or liver.98 A deficiency in PK also leads to the accumulation of 2,3 -diphosphoglycerate, the upstream metabolite of glycolysis, leading to a shift of the oxygen-hemoglobin dissociation curve to the right.99 Clinical features in newborns include anemia and hyperbilirubinemia. Symptoms can be heterogeneous, depending on the degree of enzyme deficiency and hemolysis.

Severe deficiency can lead to fetal anemia and development of hydrops fetalis.100 In peripheral blood smear, erythrocytes are typically normochromic. Polychromasia and the presence of echinocytes (RBC with small corneal projections) can be observed. 101,102 Definitive diagnosis is made using the spectrophotometric assay of erythrocyte PK activity.103 False negative results may be seen after recent transfusions or incomplete removal of white blood cells or platelets from the sample.

Additionally, given the higher levels of PK in reticulocytes, false negative results may be seen in some patients due to reticulocytosis.98 Treatment includes management of hyperbilirubinemia and anemia. Phototherapy or, in severe cases, exchange transfusion may be necessary.100 Severe anemia may require blood transfusions and splenectomy. Frequent blood transfusions can lead to iron overload and the need for iron chelation.104

Inherited GR disorders can occur at different periods of life, from pregnancy to adulthood. The severity of presentation can also vary widely from asymptomatic dysfunction to severe multisystem dysfunction requiring immediate interventions.

Significant emphasis should be placed on genetic diseases with consequent decreased production of GR such as AF, ADB, SDS and DC, as these also have anatomical anomalies and associated comorbidities that require more specialized treatments.

Determining the underlying etiology through timely diagnosis and prompt management are key to improving outcomes in newborns affected by these diseases.

Genetic counseling should be provided to parents of affected children to estimate the risk of recurrence and plan future pregnancies.

A high index of suspicion and extensive medical knowledge will help in diagnosing congenital GR disorders in due time and taking appropriate management measures to reduce morbidity and mortality.

The integrity of red blood cells is vital for neonatal health because they allow the delivery of oxygen to tissues, supporting the aerobic metabolism of all organ systems.

While physiological anemia of the newborn and anemia of prematurity are the most common causes of neonatal anemia, there are additional associated causes, including inherited RBC disorders.

Knowledge of these congenital disorders will allow a high index of suspicion for compatible signs and symptoms, allowing timely diagnosis and treatment to improve the child’s health and reduce morbidity and mortality.