. What are the types of
globin chains attached to haem pigment ?? We know that haemoglobin is a
terameric protein, composed of two kinds of globin chains. Therefore there are total four globin chains
are attached to each haem molecule. Thalassaemia by definition is quantitative
diminution of synthesis of one or two type’s globin chains. But by
haemoglobinopathies we understand there are structurally abnormal globins and
such abnormal globin chains may affect either
β, α, γ or Õ chains. These are the four types of globin chains. When to
think of abnormal haemoglobin after going through peripheral smear? Or say
Thalassemia??
1)
Microcytosis
disproportionate to the degree of anemia. 2) then one should enquire any
positive family history or lifelong personal history of microcytic anemia 3) Abnormal
red blood cell morphology with microcytes acanthocytes and target cells
Q. What to
diagnose B thalassemia?? Ans:- In B
thalassemia elevated levels of hemoglobin A2 or F
General
Considerations : The thalassemia are hereditary disorders characterized by
reduction in the synthesis of globin chains. Reduced globin chain synthesis
causes reduced hemoglobin synthesis and eventually produces a hypochromic
microcytic anemia because of defective hemoglobinization of red blood cells. Thalassemias
can be considered among the hypoproliferative anemias the hemolytic anemias and
the anemias related to abnormal hemoglobin since all of these factors play a
role in pathogenesis.
. .Q. 2: What are the three usual types of globin chains are observed in persons who carry near
normal globin moiety?? Ans: in adults there are normally three kinds of globin chains: and amount of
each globin varies person to person but the usual range is as follows:- is HbA0 (α-2,
β -2 chains ) and
this is comprises about 95-97% of all
globin moiety in a haemoglobin molecule. :
HbA2 by contrast have following globin pattern (α-2 and Õ2 chains) and
it comprises normally about 2-3% of all globins in haemoglobin. Lastly (third
variety) is HbF (comprises of
two α-chains and 2 γ chains ). HbF is < 2% of all globin chains. When only one a- globin chain is
present the patient has hemoglobin H disease. This is a chronic hemolytic
anemia of variable severity. Physical examination will reveal pallor and
splenomegaly. Although affected individuals do not usually require transfusions
they may do so during periods of hemolytic exacerbation caused by infection or
other stresses. When all four a-globin genes are deleted the affected fetus is stillborn
as a result of hydrops fetalis.
What is the
difference between Thalassaemia & Haemoglobinopathies:-:-We all know that: the thalassemia are due to a quantitative defect
in the globin chain production. Haemoglobinopathies result from a) structural
defect in the globin gene, c) whereas
the average frequency of Hb-S and Hb-D is 4.3% and 0.86%, respectively in
Indian population . HbS, HbE, and Hb D are prevalent in India..
The genetics of normal
goblin synthesis:
What about alpha chains? Such chains are governed by 4 genes all of them are
located at Chromosome 16. What about beta chains production?: Such are
controlled only by 2 genes which are located at Chromosomes 11. Beta
thalassaemia is a mutation disorder.(Alpha thalassaemia is a deletion
disorders). Normal adult hemoglobin is primarily hemoglobin A which represents
approximately 98% of circulating hemoglobin. Hemoglobin A is formed from a tetramer
two a chains and two B chains – and can be designated a2 B2 . Two copies of the
a globin gene are located on chromosome 16 and there is no substitute for a globin in the formation of hemoglobin . The
B globin gene resides on chromosome 11 adjacent to genes encoding the B like
globin chains g and y . The tetramer of a2 g2 forms hemoglobin A2 which
normally comprises 1-2 % of adult hemoglobin . The tetramer a2 y2 forms
hemoglobin F which is the major hemoglobin of fetal life but which comprises <1%
of normal adult hemoglobin .
Hemoglobin
chain disorders are principally tow kinds Type A disorders are quantitative in nature but no
structural defect in globin synthesis (thalassemia group of disorders) : There is no abnormality in
structure of globin chains. All the four globin chains are structurally normal
but the production rate of any one is at slower speed at factory
(Quantitatively low globin chains usually one chain is affected) . It is a
quantitative defect of the globin synthesis and are due to genetic defect.
.Such genetic defect (inactivation-mutant genes ) may involve either α, β or γ β chains .By contrast the beta chain
of globin manufacturing:-There are two
Varity of β thalassemia : β
thalassemia major implies both the genes
designated for β chain synthesis are defective (derived one from
each parent) and β thalassemia minor
implies only one gene entrusted with synthesis of β globin
is defective .
Thalassaemia Diagnostic dilemma:-Confirmation
of diagnosis must be done in conjunction with 1) Parental Screening,
2) DNA
study & 3) blood picture B-12
deficiency .4) Severe
Iron deficiency can lead to borderline HbA2’s . The Hb A2
results must be repeated after
correcting the Iron deficiency. Normally a man/ woman of beta Thalassemia
minor will exhibit HbA of 80-95%: HBA2 of 4-10% and HBF will be
usually in the range of 1-5%.. In cases of all thalassaemia Family studies must be done to
confirm the compound
heterozygous conditions of thalassaemia & a haemoglobinopathies together
or when the haemoglobinopathies
coexist. The results cannot be suggestive
of a particular diagnosis if the
sample was analyzed following
a blood transfusion , Most haemoglobin
variants are clinically silent. In beta
thalassemia carrier 1) to supplement full dose of F acid2) If ferritin is low
then oral Fe is indicated but by and large Blood transfusion is
contraindicated,. Unless Hb is < 8Gm near term.
What about HBE
prevalence: - This gene frequency in north eastern regions of
India has been reported to be 10.9%. In a study, the prevalence of sickle cell
disorders was found to vary from 2.4% to 5.6% among the tribes of Orissa in
eastern India / in central India, the prevalence of sickle cell disorders was
observed to be 5.7% among children.
What about the terminology of
HPLC? Hemoglobin separates into major
and minor hemoglobin’s when subjected to CE-HPLC. The order of elution of the
various components is HbA1a, HbA1b, Hb, LA1c/CHb-1, LA1c/CHb-2, HbA1c, P3 (Hb
component), HbA0, and HbA2. The minor hemoglobin’s A1a, A1b, A1C, F1, and the
P3 component are posttranslational modifications of the globing chains. HbA2, a
minor hemoglobin, however, is composed of two alpha and two delta chains. HbA0
and Hb are the major hemoglobin’s in a normal
population.
What about
HbA2 level ?? What is β-thalassemia trait? An elevated HbA2 with an average value of
about 5%, along with microcytic hypo chromic indices, is characteristic
of β-thalassemia trait in β-thalassemia major, in addition
to a markedly microcytic hypo chromic blood picture; there are elevated HbA2
and elevated Hb ranging from 10 to 90% .He trait is diagnosed by the presence
of a high HbA2 (E+A2), approximately 30% Homozygous He patients have
approximately 90% HbE+A2 with minor elevation of Hb . HbE+A2 levels of 40–60%
with marked elevation of Hb are seen in He-β-thalassemia Hobs is around 40% in sickle cell trait, 90–95% in sickle
cell anemia’s (which varies inversely with Hb proportion), and less than 50% in
sickle β-thalassemia .Approximately less
than 50% of abnormal hemoglobin is seen in Hb traits
The present study highlights the
detection of the haemoglobinopathies and thalassemia by CE-HPLC.
Type B
disorders are called Haemoglobinoathies? HbE Disorders (E Trait, EE, E β-Thalassemia)
Comparing
all the HbE disorders, it is seen that the lowest hemoglobin as well as the
highest proportion of HbF is seen in HbE β-thalassemia The
single case of HbSE disorder had a hemoglobin of 10.1 gm%, thalassemic indices
with MCV of 71fl, MCH of 23.1 pg, 36.7% of HbA2+HbE, and 2.8% of HbF.
Q.
3: What are the different kinds of haemoglobinopathies??
There is mutation of any one of the total 400 genes involved in the
synthesis of globin chains. Haemoglobin
variants are due to manufacture of abnormal globins usually one chain is
affected. Such structurally abnormal
haemoglobin are collectively called as Haemoglobinopathies .Most
important example is sickle cell disease, trait and HbC
diseases, Hb C disease, HbE trait, (20-35% HBE structurally).However HBE
trait may be very rarely combined with beta trait when it should be
investigated as Thalassaemia major.(prenatal testing like Thalassaemia major is important & recommended).
In sickle cell trait:- There is mutation of any one of
the total 400 genes involved in the synthesis of globin chains. It is due to substititution of 1 amino acid
for another one. Sometimes it may be due to deletion of a portion of amino acid
sequence: He/ She may complain of painless haematuria. Such trait has no anemia
and normal RBC morphology but higher rate of UTI / Splenic infarct.
What about Sickle Cell disease? It is basically a chr hemolytic
anemia and one glutamic acid is replaced by valine at position of 6 of the beta
globin chain. HBs? Beta thalassaemia are
not uncommonly present in Indian population (South India in particular) and in
Africa. Mild jaundice, cholelithiasis, splenomegaly are common as is
retinopathy and stroke.. Normocytic normochromic anemia with target cells,
sickled cells and ovalocytes.
.
Which method may be best used for
detection of structural abnormality of globin chains of Haemoglobin?? Ans:-
Most haematologist believe that cation
exchange-high performance liquid chromatography (CE-HPLC) is increasingly being used as a first line of investigation for haemoglobinopathies and thalassemia.
Together with a complete blood count, the CE-HPLC is effective in categorizing
haemoglobinopathies as traits, homozygous disorders and compound heterozygous
disorders.
What is the prevalence of different thalassaemia and
Haemoglobinopathies in India?? Ans: The commonest disorder in
India varies from state to state. In one study concentrating chiefly
South Indian population it was observed that
1) β-thalassemia trait (37.9%), 2) HbE trait (23.2%), 3) homozygous HbE
(18.9%), 3) HbS trait (5.3%), 4)
HbE β-thalassemia (4.6%), 5) HbS β-thalassemia (2.5%) ,6) β-thalassemia major (2.3%),7) HbH (1.6%), 8) homozygous HbS (1.4%), and HbD trait (0.7%).
When
we wil designate as Thalassemia
Trait?? The
Thalassemias are described as trait when there are laboratory features without
significant clinical impact and when
there is a red blood cell transfusion requirement or other moderate clinical
impact and major when the disorder is life threatening.
What is α
Thalassaemia ?? Ans: a-Thalassemia is due primarily to gene deletion causing reduced
a-globin chain synthesis. Since all adult hemoglobins are a containing a –
thalassemia produces no change in the percentage distribution of hemoglobins
A, A2 and F. In severe forms of a-
Thalassemia excess B chains may form a B 4 tetramer called hemoglobin H.
What
causes β Thalassemia ?? B-Thalassemias are usually caused by point mutations rather
than deletions. These mutations result in premature chain termination or in
problems with transcription of RNA and
ultimately result in reduced or absent B-globin chain synthesis . The molecular
defects leading to B- thalassemia are numerous and heterogeneous. Defects that
result in absent globin chain expression are termed B whereas those causing
reduced synthesis are termed B. The reduced B-globin chain synthesis in
B-thalassemia results in a relative increase in the percentages of hemoglobins
A2 and F compared to hemoglobin A as the B like globins substitute for the
missing B chains. In the presence of reduced B chains the excess a chains are
unstable and precipitate leading to damage of red blood cell membranes. This
leads to both intramedullary and peripheral hemolysis. The bone marrow becomes
hyperplastic under the drive of anemia and ineffective erythropoisies resulting
from the intramedullary destruction of the developing erythroid cells. In cases
of severe thalassemia the marked expansion of the erythroid element n the bone
marrow may cause severe bony deformities osteopenia and pathologic fractures.
How do we diagnose
Beta Thalassaemia?? What may be preliminary Clinical Findings?
A.
Symptoms
and Signs
The a- thalassemia syndromes are seen primarily in persons
from southeast Asia and China and less commonly in blacks. Normally adults have
four copies of the a-globin chain. When three a- globin genes are present the
patient is hematologically normal. When two a- globin genes are present the
patients is said to have a thalassemia
trait one form of thalassemia minor. These patients are clinically normal and
have a normal life expectancy and performance status with a mild microcytic
anemia.
Global Location: Zone of high prevalence:-B-Thalassemia
primarily affects persons of Mediterranean origin and to a lesser extent Asians
and blacks. Patients homozygous for B- thalassemia have thalassemia major .
Affected children are normal at birth but after 6 months when hemoglobin
synthesis switches from hemoglobin F to hemoglobin A, develop severe anemia
requiring transfusion. Numerous clinical problems ensue including growth
failure bony deformities hepatosplenomegaly and jaundice. The clinical course
is modified significantly by transfusion therapy but the transfusional iron overload results
in a clinical picture similar to hemochromatosis with heart failure cirrhosis
and endocrinopathies usually after more than 100 units of red blood cells.
These problems develop because of the body’s inability to excrete the iron from
transfused red cells. Before the application of allogeneic stem cell
transplantation and the development of more effective forms of iron chelation
death from cardiac failure usually occurred between the ages of 20 and 30 years
. This has been profoundly changed by the early application of transplantation
.
What do U man by homo/heterozygosis?? Patients homozygous for
a milder form of B- thalassemia have Thalassaemia intermedia. These patients
have chronic hemolytic anemia but do not require transfusions except under
periods of stress. They also may develop iron overload because of periodic
transfusion. They survive into adult life but with hepatosplenomegaly an bony
deformities minor and a clinically insignificant microcytic anemia.
Is it possible to diagnose by prenatal methods? When such
tests become necessary? What is these nionivaaive method now available for diag
Thal major( Prenatal diagnosis is available and genetic counseling should be
offered and the opportunity for prenatal diagnosis discussed What are the
informations we gather from cell free DNA (foetal cells citculatimg in maternal
blood) ?? .
What do U expect if U send the blood to A REPUTED LAB? Have
lab reports of this indoor pt been
supplied by te invigilators to you,
my dear candidate?? Have seen the
Laboratory Findings already done?
What is α-Thalassemia trait- Patients with two a- globin genes have mild anemia with hematocrits
between 28% and 40% . The MCV is strikingly low despite the modest anemia and
the red blood count is normal or increased. The peripheral blood smear shows
microcytes hypochromic occasional target cells and acanthocytes . The
reticulocytes count and iron parameters are normal. Hemoglobin electrophoresis
will show no increase in the percentage of hemoglobin A2 or F and no hemoglobin
H a- thalassemia trait is thus usually
diagnosed by exclusion . Genetic testing to demonstrate a- globin gene deletion
is available only in research laboratories.
2 A very rare diseases is HB H diseases? Have U heard the name of
it?? Hemoglobin H disease- These patients have a more marked hemolytic anemia with hematocirts
between 22% and 32%.The MCV is remarkably low and the peripheral blood smear is
markedly abnormal with hypochromia microcytosis target cells and
poikilocytosis. The reticulocye count is elevated . Hemoglobin electdrophoresis
will show the presence of fast migrating hemoglobin which comprises 10-14 % of
the hemoglobin. A peripheral blood smear can be stained with supravital dyes to
demonstrate the presence of hemoglobin H.
What U do know about β-Thalassemia minor-not an uncommon condition in N E India?? – As in a thalassemia trait these patients
have a modest anemia with hematocrit between 28% and 40% . The MCV ranges from 5 to 75 ft and the red
blood cell count is normal or increased. The peripheral blood smear is mildly
abnormal with hypochromia Microcytosis
and target cells. In contrast to a – thalassemia basophilic stippling may be
present. The reticulocytes count is normal or slightly elevated. Hemoglobin
electrophoresis may show an elevation of hemoglobin A2 to 4-8% and occasional
elevations of hemoglobin F to 1-5%
4:-Thalassemia major – B- Thalassemia major produces severe
anemia and without transfusion the hematocrit showing severe poikilocytosis
hypochromia microcytosis target cells basophilic stippling and nucleated red
blood cells. Little or no hemoglobin A is present Variable amounts of
hemoglobin A2 are seen and the major hemoglobin present a hemoglobin F.
Thal trait? Treatment
Patients with mild thalassemia require no treatment and
should be identified so that they will no be subjected to repeated evaluations
and treatment for iron deficiency. Patients with hemoglobin H disease should
take folate supplementation and avoid medicinal iron and oxidative drugs such
as sulfonamides. Patients with severe thalassemia are maintained on a regular
transfusion schedule and receive folate supplesmentation. Splenectomy is
performed f hypersplensim causes a marked increase in the transfusion
requirement . Patients with regular transfusion requirements should be treated
with iron chelation in order to prevent life limiting organ damage from iron
overload. Subcutaneous infusion of deferoxamine has largely been replaced by
the oral agent deferasirox.
What about Marrow Transplantation?? Allogenic bone marrow
transplantation is the treatment of choice for B- thalassemia major. Children
who have not yet experienced iron overload and chronic organ toxicity do well
with long term survival in more than 85% of cases.
General Considerations.
U are doing well . Wee
the examiners are happy with your answer. But can U tellus what do U mean by
the term sideroblastic anemia ??
Sideroblastic anemias are a heterogeneous group of disorders in which
hemoglobin synthesis is reduced because of failure to incorporate heme into
protoporphyrin to form hemoglobin. Iron accumulates particularly in the
mitochondria. The disorder is usually acquired it is most often a subtype of
myelodysplasia . Other causes include chronic alcoholism and lead poisoning.
What are the Clinical
Finding of Sideroblastic anemias?? Any
idea dear examinee??
Patients
have no specific clinical features other than those related to anemia. The
anemia is usually moderate with hematocrits of 20-30% but transfusions may
occasionally be required. Although the MCV is usually normal or slightly
increased it may occasionally be low, leading to confusion with iron
deficiency. However, serum iron level is elevated and transferrin is high. The
peripheral blood smear characteristically shows a dimorphic population of red
blood cells, one normal and one hypochromic. In cases of red poisoning, coarse
basophilic stippling of the red cells is seen and the serum lead levels will be
elevated. The diagnosis is made by examination of the bone marrow.
Characteristically, there is marked erythroid hyperplasia, a sign of
ineffective erythropoieis (expansine of the erythroid compartment of the bone
marrow that dose not result in the production of reticulocytes in the
peripheral blood ). The Prussian blue iron stain of the bone marrow shows a
generalized increase in iron stors and the presence of ringed sideroblasts,
which are cells with iron deposite encircling the red cell nucleus. Occasionally,
the anemia is so severe that support withtransfusion is required. These
patients usually do not respond will to erythropoietin therapy, especially when
transfusion requirements are significant
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