Ban mốc anh.docx1/ 8Endocrine and Bone Complications in -ThalassemiaIntermedia: Current Understanding and Treatment1. Introduction-thalassemia, one of the most common monogenetic diseases worldwide, constitutes a group of hereditary blood disorders resulting from a defect in the synthesis of the - globin chain [1, 2]. This defect causes a disproportionate ratio of alpha- and beta-globin chain synthesis leading to ineffective erythropoiesis (IE) and a chronic hemolytic anemia. Based on genetic and clinical features, -thalassemia is divided into 3 distinct categories: thalassemia major, thalassemia intermedia, and thalassemia minor. Patients with -thalassemia major (-TM) harbor two defective copies of the -globin chain and present during the first 2 years of life with a severe lifelong transfusion dependent microcytic anemia. People with thalassemia minor or the carrier state have one defective copy of the -globin chain (heterozygous) and are usually clinically silent [1–3]. Beta thalassemia intermedia (-TI) is a disease of intermediate severity where affected patients usually present with a later onset of microcytic anemia and milder clinicalsymptoms compared to -TM. It belongs to the nontransfusion dependent thalassemia (NTDT) group which also includes -thalassemia intermedia (hemoglobin H disease) and hemoglobin E/-thalassemia (mild and moderate forms). It arises from a homozygous or a compound heterozygous mutation leading to partial suppression of betaglobin protein production.Three mechanisms are responsible for the milder phenotype of -TI: inheritance of a mild or silent beta-chain mutation, coinheritance of -thalassemia, and hereditary persistence of HbF, -thalassemia, and G XMN1 polymorphism [2–4].The clinical manifestations and complications of -TI are unique and different from well treated -TM patients but are similar to -TM patients who are poorly transfused. Hence, it is plausible that the manifestation of -TI are due to dyserythropoiesis. The disease is characterized by marked phenotypic heterogeneity with some patients remaining asymptomatic and maintaining a baseline hemoglobin range of 7–10 g/dL, while some others requiring transfusions due mostly to suboptimal growth and development, skeletalResearch International deformity, exercise intolerance, and declining hemoglobin levels because of progressive splenomegaly. Typical physical exam findings include growth retardation, thalassemic bone deformities, splenomegaly, and moderate to severe hepatomegaly [2, 3, 5].The triad of chronic anemia, ineffective erythropoiesis, and iron overload characterizes -TI and is mostly responsible for its clinical sequelae. Other disease complications include endocrinopathies, bone disorders, and end organ damage. Some complications as extramedullary hematopoiesis, leg ulcers, gallstones, thrombosis, and pulmonary hypertension, are rarely encountered in -TM, but frequently seen in -TI [2–4, 6, 7]. Older age and splenectomy have been shown to be independently associated with an increased risk of most -TI disease-related complications [8, 9]. Much of the disease associated morbidity and mortality can be reduced withregular surveillance, early treatment, and follow-up in a comprehensive multidisciplinary setting.Treatment of -TI needs to be individualized and tailored to the patient’s clinical scenario. Conventional treatment consists of transfusions, iron chelation, splenectomy, supportive therapies, and psychological support.Nonconventional treatment includes hematopoietic stemcelltransplantation which remains to be the only curative treatment, fetal hemoglobin modulation, and gene therapy [2, 4, 5, 9].In this review, we shall cover two of the major complications encountered in -TI: endocrine andbone complications. We will also shed light on iron overload in -TI as well as other mechanismsthat may lead to these complications.2. Iron Overload in �-TIIron overload in �-TI is multifactorial and attributed primarily to increased gastrointestinal iron absorption [10]. It can also result from chronic hemolysis and occasional blood transfusions required to treat disease complications [10, 11]. In response to chronic anemia and ineffective erythropoiesis, levels of growth and differentiation factor 15 (GDF 15), twisted gastrulation factor 1, and hypoxia-inducible transcription factors (HIFs) increase leading to hepcidin suppression and ferroportin and erythropoietin upregulation [11–14].Theoutcome is an increase in duodenal iron absorption and release of iron from the reticuloendothelial system [11]. Increased gastrointestinal iron absorption, coupled with transfusions, leads to iron overload. Even though iron overload occurs in patients with �-TI at a much slower rate than that in those with regularly transfused �-TM, with advancing age, it can reach levels much higher than normalthresholds with markedly elevated liver iron concentration (LIC) and high levels of circulating toxic non-transferrin-bound iron (NTBI). Serum ferritin levels and LIC determined by R2 and R2∗ magnetic resonance imaging (MRI) positively correlate in �-TI patients [15–17] where 800 and 300 ng/mL of serum ferritin correspond to 5mg and 3 mgs Fe/g dry weight (DW) [18]. Vascular, endocrine, and bone morbidity in �- TI has been shown to be significantly associated with serum ferritin more than 800 ng/mL and LIC more than 6-7 mg Fe/g DW [18–21]. Spot ferritin measurements, however, may underestimate the burden of iron overload and subsequently delay therapy [20]. LIC, which is the reliable and noninvasive gold standard, approximates iron overload better than serum ferritin [16, 20, 22, 23]. If untreated, iron overload will lead to organ dysfunction involving mostly the liver, heart, and endocrine organs and a wide spectrum of complications and clinical outcomes. A recent study (THALASSA) on 95 patients with NTDT showed efficacy of the once daily oral iron chelator deferasirox in patients at least 10years of age with LIC ≥ 5mg Fe/g DW and serum ferritin of at least 800 ng/mL [18]. Despite the availability of chelation therapy including oral agents, iron overload remains a problem because of poor adherence to chelation regimens and high cost of such treatment.3. Endocrine Complications in �-TIEndocrine complications are amongst the most common complications in �-TI and are mostly attributed to iron overload and suboptimal chelation [2–4, 6, 24]. They are associated with splenectomy, increasing age, severe ineffective erythropoiesis, and low fetal hemoglobin levels [9, 24]. The frequency of these complications is lower than that in �-TM and varies greatly according to severity of the anemia and iron overload [25]. Earlier onset of these complications is observedwithhigher LICcomparedtolower concentrations [21] and a lower frequency has been observed in patients on iron chelation therapy and or on hydroxyurea [9]. However, no relationship could be established between endocrine dysfunction and serum ferritin level, age of start of desferrioxamine, and hemoglobin level [26, 27]. The most frequent endocrine complications reported in �-TI are growth retardation, delayed puberty, hypogonadism, diabetes, impaired thyroid, parathyroid and adrenal functions, and dyslipidemias. Early recognition and treatment of endocrine complications is important in order to prevent late irreversible sequelae and increase the chances of successful reproduction. Patients with established endocrine disease should be referred to an endocrinologist and managed according to recommendations in �-TM patients [2, 4, 6, 24, 26, 27]. The sections below will offer a detailed up to date review of the most frequent endocrine complications encountered in �-TI. They will also summarize important recommendations for screening and management of these complications and highlight the 2013Thalassemia International Federation (TIF) Guidelines for the Management of NTDT [24].3.1. Growth Retardation. The prevalence of short stature in children and adults with thalassemia is approximately 25% regardless of the type of the thalassemia and serum ferritin concentration [25]. 20%–30% of thalassemic patients have growth hormone (GH) deficiency and 70–80% havepeak growth hormone (GH) levels on provocative tests lower than those seen in patients with constitutional short stature [28]. In �-TI, growth hormone deficiency is seen in 31%of patients (28) while the prevalence of short stature (height more than 2 SD below man height for age (below 3rd percentile)) varies between reports ranging from 7 to 46% [26, 27]. In children and adolescents, hypogonadism has been shown to be associated with short stature and GH deficiency to be a significant negative predictor of height. In adults, GH deficiency was the only significant predictor of short stature [25].The pathogenesis of growth failure in thalassemia is multifactorial and is mainly due to transfusional iron overload and resulting endocrinopathies (GH deficiency, hypothyroidism diabetes), nutritional deficiencies, and intensive use of chelating agents particularly desferrioxamine. Other aetiologies particularly in suboptimally treated children are increased metabolism, chronic anemia, and hypoxia. The anterior pituitary is particularly sensitive to iron associated free radical oxidative stress. Even a modest amount of iron deposition in the anterior pituitary byMRI can interfere with its function. Dysregulation of the GH insulin like growth factor axis leads to growth hormone deficiency and growth deceleration [25, 28]. All patients with NTDT including those with �-TI who are ≥10 years should undergo standing and sitting height every 6 months, bone age, growth hormone stimulation, insulin-like growth factor (IGF)-1level, and IGF-BP3 level (in patients who fall-off the growth curve (5%) and have decreased height velocity or delayed bone age, desferrioxamine toxicity, and other
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