tailieunhanh - Chapter 099. Disorders of Hemoglobin (Part 12)

The homozygous state for the α-thalassemia-1 cis deletion (hydrops fetalis) causes total absence of α-globin synthesis. No physiologically useful hemoglobin is produced beyond the embryonic stage. Excess γ-globin forms tetramers called Hb Barts (γ4), which has a very high oxygen affinity. It delivers almost no O 2 to fetal tissues, causing tissue asphyxia, edema (hydrops fetalis), congestive heart failure, and death in utero. α-Thalassemia-2 trait is common (15–20%) among people of African descent. The cis α-thalassemia-1 deletion is almost never seen, however. Thus, α-thalassemia-2 and the trans form of α-thalassemia-1 are very common, but HbH disease and hydrops fetalis. | Chapter 099. Disorders of Hemoglobin Part 12 The homozygous state for the a-thalassemia-1 cis deletion hydrops fetalis causes total absence of a-globin synthesis. No physiologically useful hemoglobin is produced beyond the embryonic stage. Excess y-globin forms tetramers called Hb Barts y4 which has a very high oxygen affinity. It delivers almost no O2 to fetal tissues causing tissue asphyxia edema hydrops fetalis congestive heart failure and death in utero. a-Thalassemia-2 trait is common 15-20 among people of African descent. The cis a-thalassemia-1 deletion is almost never seen however. Thus a-thalassemia-2 and the trans form of a-thalassemia-1 are very common but HbH disease and hydrops fetalis are almost never encountered. It has been known for some time that some patients with myelodysplasia or erythroleukemia produce RBC clones containing HbH. This phenomenon is due to mutations in the ATRX pathway that affect the LCR of the a-globin gene cluster. Diagnosis and Management of Thalassemias The diagnosis of ß-thalassemia major is readily made during childhood on the basis of severe anemia accompanied by the characteristic signs of massive ineffective erythropoiesis hepatosplenomegaly profound microcytosis a characteristic blood smear Fig. 99-5 and elevated levels of HbF HbA2 or both. Many patients require chronic hypertransfusion therapy designed to maintain a hematocrit of at least 27-30 so that erythropoiesis is suppressed. Splenectomy is required if the annual transfusion requirement volume of RBCs per kilogram of body weight per year increases by 50 . Folic acid supplements may be useful. Vaccination with Pneumovax in anticipation of eventual splenectomy is advised as is close monitoring for infection leg ulcers and biliary tract disease. Many patients develop endocrine deficiencies as a result of iron overload. Early endocrine evaluation is required for glucose intolerance thyroid dysfunction and delayed onset of puberty or secondary sexual .

• Y học thường thức
• Disorders of Hemoglobin
• bệnh học và điều trị
• bài giảng bệnh học
• tài liệu học ngành y
• Harrisons Internal Medicine
• Harrisons principles of internal medicine
• Internal medicine
• Quality of health care
• Developed countries
• Health care systems
• Chest discomfort
• Clinical medicine
• The cardiovascular system
• Critical care medicine
• The kidney and urinary tract
• The gastrointestinal system
• The joints and adjacent tissues
• Neoplasms of the Lung
• tài liệu y khoa
• bệnhbệnh học và điều trị
• Sodium and Water học và điều trị
• General considerations in clinical medicine
• Cardinal manifestations
• Presentation of diseases
• The environment and disease
• Regenerative medicine
• Introduction to clinical medicine
• The environment
• Disorders of the cardiovascular system
• Disorders of the respiratory system
• Disorders of the gastrointestinal system
• Infectious diseases
• The respiratory system
• Neurologic Disorders
• Moraxella Infections
• Haemophilus Infections
• Bệnh truyền nhiễm
• Tim mạch
• Tiết niệu
• Tiêu hóa
• Cơ xương khớp
• Acute rheumatic fever
• Antiphospholipid syndrome
• Inflammatory myopathies
• Relapsing polychondritis
• Pituitary tumor syndromes