All of the following are true about β thalassemia trait, Except: (PGI Nov2008)
|A||Microcytic hypochromic picture|
|D||Patient requires blood transfusion|
Patient requires blood transfusion
1. Hemoglobin consists of 2 different pairs of peptide chains (one alpha and the other beta) with the haem molecule attached to each peptide.
2. Adults have 95% HbA (α2β2) + 5% HbA2 (α2δ2).
3. Fetuses have HbF (α2γ2) which continues to persist in beta – thalassanemia
4. In thalassemias, there is a reduced rate of production of one or more globin chains leading to precipitation of globin, and anemia occurs as a result of ineffective erythropoiesis and hemolysis.
Extra Edge: (Ref. Hari-18th ed., Pg. 61, table 99.4)
1. Alpha thalassanemia (reduced production of alpha chains)
2. Beta thalassanemia (reduced production of beta chains)
3. Hemoglobin H disease
4. Hb Barts
5. Beta thalassemia intermedia.
Beta-thalassemia (β-thalassemia) is a form of thalassemia due to mutations in the HBB gene on chromosome 11, inherited in an autosomal recessive fashion.
1. The severity of the disease depends on the nature of the mutation.
2. Alleles without a mutation that reduces function are characterized as (β).
3. Mutations are characterized as (βo) if they prevent any formation of β chains.
4. Mutations are characterized as (β+) if they allow some β chain formation to occur. (Note that the "+" in β+ is relative to βo, not β.)
5. In either case there is a relative excess of α chains, but these do not form tetramers: rather, they bind to the red blood cell membranes, producing membrane damage, and at high concentrations they form toxic aggregates
Any given individual has two β globin alleles:
β thalassemia minor
(Also called β thalassemia trait)
1. If only one β globin allele bears a mutation.
2. There is a mild microcytic anemia.
3. MCV a slightly decreased.
4. iv. The patient will have an increased fraction of Hb A2 (>3.5%) and a decreased fraction of HbA (<97.5%).
β+/β or βo/β
1. A condition intermediate between the major and minor forms.
2. ii. Affected individuals can often manage a normal life without need for transfusions.
β thalassemia major or Cooley's anemia
1. If both alleles have thalassemia mutations.
2. This is a severe microcytic, hypochromic anemia.
3. Untreated, it causes anemia, splenomegaly, and severe bone deformities.
4. It progresses to death before age twenty. Treatment consists of periodic blood transfusion;
5. Splenectomy if splenomegaly is present, and treatment of transfusion-caused iron overload.
6. vi. Cure is possible by bone marrow transplantation.
β+/βoor βo/βo or β+/β+
Note that β0/β can be associated with β thalassemia minor or β thalassemia intermedia, and β+/β+ with thalassemia major or intermedia.
The genetic mutations present in β thalassemias are very diverse, and a number of different mutations can cause reduced or absent β globin synthesis. Two major groups of mutations can be distinguished:
1. Nondeletional forms: These defects generally involve a single base substitution or small deletion or inserts near or upstream of the β globin gene.
2. Most commonly, mutations occur in the promoter regions preceding the beta-globin genes.
3. Less often, abnormal splice variants are believed to contribute to the disease.
4. Deletion forms: Deletions of different sizes involving the β globin gene produce different syndromes such as (βo) or hereditary persistence of fetal hemoglobin syndromes.
Types of Beta thalassemia
1. Beta – Thalassanemia Major (Homozygotes)
a. Anemia is very severe and the patients live only for a short time without blood transfusion.
b. Bone marrow hyperplasia produces frontal bossing and prominent malar eminences which is seen in the skull X – ray as ‘hair on end’ appearance.
c. Children develop characteristic "chipmunk" facies due to maxillary marrow hyperplasia and frontal bossing.
d. Most types of beta thalassemia are caused by point mutations affecting one or few bases.
e. M/C point mutation in beta thalassemia involves IVS-1 or the intron – 1
2. Thalassemia Intermedia
a.The patient presents with features which are intermediate between thalassemia major and thalassemia minor.
b.The symptoms are milder than those of thalassemia major but severe than those of usually asymptomatic thalassemia minor. Important characteristic features of thalassemia intermedia are:
c.Conventionally the condition is considered non-transfusion dependent, the patient is capable of surviving without transfusion.
d.The growth and development in the patient is usually normal. The common presenting features are:
i. Anemia of mild to moderate degree (7 -10 g/dl), less than 7-8 degrees indicates severe cases.
ii. Mild jaundice.
iii. Splenomegaly (the spleen is palpable from the beginning and its size increases with time).
3. Beta – Thalassanemia Minor (Heterozygotes)
The course is very mild and often this anemia is detected only when a therapy for a mild hypochromic anemia fails. Symptoms are minimal
↑ HbF, ↑ HBA2, usually asymptomatic and S. ferritin is normal