Week 1 - F - Haemaglobinopathy - Major forms of Hb, Thalassemia (alpha trait, Hbh, Barts HYdrops/ Beta trait, intermedius, Major), Sickle cell disease

Question 1

What is the structure of adult haemoglobin?

Answer 1

HbA is a tetramer made up of 2alpha globulin like chains and 2beta globulin like chains One haem molecule (containing a prophyrin ring and iron Fe2+) bind to each globulin

Question 2

What are the major forms of haemoglobin in adults? and their percentages? WHat is the main form of haemoglobin in adults?

Answer 2

HbA - 2alpha 2beta chains - 97% HbA2 - 2 alpha, 2delta chains - 2.5% HbF - 2alpha, 2gamma chains - 0.5% The main form of haemoglobin in adults is hameoglobin A

Question 3

Just throwing in the question, What chromosome holds the genes for A,B andO? What chromosome holds the genes for RhD protein?

Answer 3

ABO substances - chromosome 9 RhD protein (D and d) - chromosome 1

Question 4

Genetic control of globin chain production Where are the alpha like genes located? Where are the beta like chains located? ie which chromsomes How Many genes are their per chromsome for both of the above chromosomes and therefore how many genes for each chromosome per cell?

Answer 4

Alpha genes are located on chromosome 16 There are 2 genes per chromosome and therefore each cell contains 4 alpha genes Beta genes are located on chromosome 11 (gamma is also on chromosome 11) There is only 1 gene per chromosome and therefore each cell contains 2 beta genes

Question 5

Expression of globin genes changes during embryonic life and childhood The genes are arranged in order of this expression The haemoglobin that exists during embryo (HbE)is known as Haemoglobin Gower and Portland When does this haemoglobin become foetal haemgolobin (HbF)?

Answer 5

At 10-12 weeks of development, the foetus primary source of haemoglobin switches from embryonic to foetal haemoglobin

Question 6

At 10-12 weeks when the embryonic haemoglobin becomes the foetal haemoglobin, what are the globulin involed in HbF? When is does haemoglobin reach adult levels? What are the types of adult haemoglobin?

Answer 6

HbF - 2alpha, 2 gamma globilins Adult haemoglobin levels reached by 6-12 months of age HbA - 2alpha, 2 beta = 97% HbA2 - 2alpha, 2delta = 2.5% HbF - 2alpha, 2gamma = 0.5%

Question 7

In adults, fetal hemoglobin production can be reactivated pharmacologically, which is useful in the treatment of diseases such as what? What drug is used to reactivate the foetal haemoglobin production?

Answer 7

Foetal haemoglobin may be reactivated in diseases such as sickle cell anemia Hydroxycarbamide is the drug used to reactive foetal haemoglobin production

Question 8

During foetal development gamam globulin production rises to around birth before continually falling until HbA is the main Hb What are hereditary conditions affecting globin chain synthesis known as?

Answer 8

Hereditary conditions affecting globin chain synthesis are usually known as haemaglobinopathies

Question 9

What mode of inheritance are haemaglobinopathies usually?

Answer 9

Haemaglobinopathies are usually autosomal recessive conditons

Question 10

Haemaglobinopathies - hereditary conditions affecting globin chain synthesis and this is usually autosomal recessive What are the two main groups of haemoglobinopathies?

Answer 10

Thalassemia - this is where there is a decreased rate of globin chain synthesis Structural haemoglobin variants - normal production of structurally abnormal globin chains - variant haemoglobin (HbS)

Question 11

Reduced globin chain synthesis resulting in impaired haemoglobin production What is this?

Answer 11

This is thalassemia

Question 12

Thalassemia can be classified as Alpha thalassemia - alpha chain affected or Beta thalassemia - beta chain affected What is the difference of cause of alpha and beta thalassemias?

Answer 12

Alpha thalassemias usually are caused by whole gene deletions which code for alpha globulins on chromsome 16 whereas Beta thalassemias usually are caused by point mutations in B-globulin genes on chromsome 11

Question 13

What type of anaemia caused by the inadequate haemoglobin production in thalassemia?

Answer 13

This will cause microcytic hypochromic anaemia

Question 14

Unbalanced accumulation of globin chains is toxic→ ineffective erythropoiesis and haemolysis Reduced globin chains - reduced haemoglobin - reduced red blood cells - increase in haemolysis What are the most common inherited single-gene disorders in the world? (commonest monogenic disorders)

Answer 14

The commonest monogenic disorders worldwide are alpha and beta thalassemias

Question 15

What areas is thalassemia most common in? What ethnic groups?

Answer 15

Thalassemia is common in areas where malaris is or was present It is most common in people of Mediterranean origin (for beta thalessemias) or from the far east (for alpha thalassemias)

Question 16

Alpha thalassemia is caused by mutations affected alpha globin chain synthesis How may alpha globulins do normal individual have? What causes alpha thalassemia?

Answer 16

Normal individuals have 4 alpha globulins per cell (2 from each parents chromosome 16) Alpha thalassemia is caused by a deltion in one (a+) or both (a0) of the alpha genes on chromsome 16

Question 17

Alpha thalassemia Reduced α+ or absent α0 synthesis of α chains Results from deletion of one α+ (-α) or both α0 (–) alpha genes from chromosome 16 α chains present in all adult forms of Hb therefore HbA, HbA2 and HbF all affected What are the different classifications of alpha thalassemia?

Answer 17

α thal trait; one or two genes missing * α+/α (-α/αα) * α0/ α (–/αα) * α+/α+(-α/-α) HbH disease; only one alpha gene left α0/α+(–/-α ) Hb Barts hydrops fetalis; no functional α genes α0/α0 (–/–)

Question 18

How is alpha thalassemia trait written? (alpha thal trait) What are the symptoms? What is different about this persons blood results?

Answer 18

Alpha thalassemia would be written * a0/aa (–/aa) (that means only two alpha genes affected) or * a+/a+ (-a/-a) still two genes affected or * a+/aa (-a/aa) - only one alpha gene affected These people are usually asymptomatic The patient will have a low MCV, and have hypochromic red blood cells with mild anaemia

Question 19

No treatment usually required for alpha thalassemia trait as only a mild degree of anaemia - it is important to distinguish this from iron deficiency anaemia How is this done? (difference in ferritin and RBC)

Answer 19

In iron deficiency anaemia - the MCV would also be decreased But the ferritin levels would be low and the RBC count will be low In alpha thal trait, MCV is low, but ferritin is normal and RBC high

Question 20

Why is the red blood cell count low in IDA but high in alpha thal trait?

Answer 20

Low in IDA - this is because there isnt enough iron in the body to produce Hb and red cells therefore the count is decreased High in alpha thal trait - this is because there is only a decrease in the globulin therefore the haemoglobin cant carry as much oxygen but no deificnecy in the compounds that make up Hb - therefore erythroid hyperplasia will produce more RBCs to try and counteract the hypoxia - high RBC

Question 21

The severe form of alpha thalassemia occurs when there are 3 alpha gene deletions on chromsome 16 What are the blood findings here? What is this form of alpha thalassemia known as? WHy is it known as this?

Answer 21

This is where there is only one working alpha gene Patient has a very low MCV and MCH This form of alpha thalassemia is known as HbH disease It occurs because the excess beta chains form tetramers known as HbH and these cannot carry oxygen

Question 22

When examining the cells in HbH disease, what do the special stains reveal?

Answer 22

When examining the cells under a special stain - it reveals golf ball cells - these are red cell inclusions of HbH

Question 23

What are the clinical features of HbH disease?

Answer 23

Slplenomegaly due to extramedullary haemtopoiesis - Bone marrow is working overtime to try and compensate for the anaemai but it cant – therefore in red cell production in other places like the spleen Jaundcie due to haemolysis as the cells die early Moderate to severe anaemia

Question 24

What is the only way to inherit Hamegolobin H disease? What is the usual treatment of the disease?

Answer 24

Only way to inherit it is if from one parent you get zero copies of alpha a0 and from the other you get a Usual treatment is blood transfusions Splenectomy should be performed only in the presence of manifest hypersplenism, because it is associated with increased thromboembolic complications.

Question 25

What should be be measured throughout the treatment of HbH disease?

Answer 25

Measure the ferritin levels as iron overload may occur and treatment with an iron cheleating agent may be required

Question 26

What is the severest form of alpha thalassemia?

Answer 26

This would be Hb Barts Hydrops Foetalis In this case, all 4 alpha genes on chromosome 16 have been deleted resulting in severe haemolytic microcytic anaemia

Question 27

No α genes inherited from either parent α0/α0(–/–) Minimal or no α chain production →HbA can’t be made What will be the majority of haemoglobin at birth in someone with Hb Barts Hydrops Foetalis?

Answer 27

The majority of haemoglobin would be Hb Barts (y4) - this is where gamma chains form tetramers and HbH (b4) - beta chains form tetramers Neither can carry oxygen

Question 28

What happens to babeis with Hb Barts Hydrops Foetalis?

Answer 28

As alpha chains are major constituentts of HbF and HbA, the baby is likely to die in utero due to profound anaemia, growth retardation, cardiac abnormalities, severe hepatosplenomegaly Hepatosplenomegaly due to the increased haemolysis of cells - also as bone marrow is working overtime for erythropoeisis, the liver and spleen may join in, in a futile attempt to produce RBCs

Question 29

Beta thalassemia Reduced ( β+), or absent ( β0 ) beta chain Disorder of beta chain synthesis What causes it? Which type of haemoglobin is affected?

Answer 29

It is caused by a point mutation in the beta chains on chromosome 11 Therefore causing reduce B+ or absent B0 from the parents Only HbA is affected as only the beta chains are affected and beta globulins are only involed in adult haemoglobin

Question 30

Where as alpha thal is due to deleting the entire gene Beta thal is only due to a point mutation in the gene Where are the highest carriers for beta thalassemia? What are the different types of beta thalasemmia?

Answer 30

The highest incidence of beta thalassemia is in the far east - ie south east asia and cyprus Different types - Beta thalassemia minor or trait - usually mild B thal from one parent and a normal from the other Beta thalassemia intermedia - more anemia – usually both parents have mild mutations Beta thalassemia major - when both parent shave the absence of Beta chains (B0/B0)

Question 31

Beta thalassemia trait (B+/B or B0/B) How does it present? What haemoglobin is usually raised?

Answer 31

This is asymtpomatic and usually no/mild anaemia Usually there is a low MCV with a raised HbA2 (>3.5%) (sometimes also HbF)

Question 32

β thalassaemia intermedia (β+ /β+ or β0 /β+) How does this tend to present and what are the treatment options?

Answer 32

Usually presents with mild to moderate anaemia with low MCV, can occasionally require blood transfusions

Question 33

When does Bthalassemia major present? How does it present? What does the haemoglobin analysis show?

Answer 33

Present usually within the first year (6-24 months) as the HbF begins to fall off Failure to thrive as well as extramedullary haemtopoesis causing hepatosplenomegaly and skull bossing

Question 34

Where is the normal sites of haematopeoisis? What can extramedullary haematopoeisis in the skull cause? What is the sign on xray with this known as?

Answer 34

Normal sites - bone marrow Skull Sternum Ribs Pelvis Proximal femur The extramedullary haematopoiesis in the skull can cause spinal cord compression Sign on the x-ray is known as the hair-on edge sign - this is due to the icnrease in marrow activity

Question 35

The management of beta thalassemia major is regular transfusions What does this aim to achieve? What haemoglobin level is attempted to maintain?

Answer 35

The regular tranfusion programme ainms to maintain Hb at 95-105g/L This is in the attempt to restore oxygen to the cells Whilst reducing over abosorption of iron and Suppressing the ineffective eryhtropoeisis

Question 36

Simplest way to treat is by putting the patient on a haemoglobin transfusion programme Effectively switches off the ineffective erythropoiesis and over absorption of iron The problem then arises from the iron overlaod from the transfusion - only a matter of time Why is there an iron overload when treating with transfusions?

Answer 36

This is because normally there is only 1mg of iron absorbed per day and 1mg excrete When giving transfusions, about 250mg of iron per unit of red cells There is no escape mechanism of iron as it is a closed cycle and therefore iron overload will result from this regular transfusion - too much iron in blood as well as stored in the marrow and macrophages

Question 37

Bone marrow transplant may be an option if carried out before complications develop What are the complications of iron overload? (heart, endocrine, liver)

Answer 37

Cardiac disease * Cardiomyopathy * Arrhythmias Endocrine dysfunction * Impaired growth and pubertal development * Diabetes * Osteoporosis Liver disease * Cirrhosis * Hepatocellular cancer

Question 38

250mg of iron per unit of red cells Chronic anaemia drives increased iron absorption Venesection not feasible – already anaemic! Therefore managing iron overload can happen using what?

Answer 38

Medications used in chelation therapy are known as chelating agents. Chelators bind to iron, complexes formed are excreted in urine or stool

Question 39

What re examples of chelating agents used in the management of iron overload? What is the route of administration?

Answer 39

desferrioxamine (DFO) – taken using a pump that slowly feeds the medicine through a needle into the skin (infusion) over 8-12 hours, five or six times a week deferiprone (DFP) – taken as a tablet or liquid three times a day; it’s sometimes used alongside DFO to reduce the number of infusions you need deferasirox (DFX) – taken once a day as a tablet that you dissolve in a drink

Question 40

What are the risks of continual transfusions?

Answer 40

The risk include * Viral infections * Transfusion reactions (immediate, delayed, febrile) * Allo antibody formation * Fluid overload * Bacterial

Question 41

If the hypersplenism persists depsite increasing transfusions, a splenectomy may have to be carried out? When is this best avoided until? What is the only treatment cure in thalassemia? (has major risks)

Answer 41

This is best avoided until 5years of age due to removing the spleen greatly increasing the risk of infection Splenomegaly usually develops in patients with beta-thalassaemia major as a result of multiple transfusions, iron deposition,& some ineffective extramedullary erythropoiesis (especially in inadequately transfused patients). This usually results in hypersplenism, leading to an increase in transfusion requirement secondary to decreased red cell survival, as well as leukopenia and thrombocytopenia Stem cell or bone marrow transplant - only treatment of cure

Question 42

The spleen contains macrophages which filter and phagocytose bacteria As splenectomy increases the lifelong risk of infections what prophylactic antibitoics should be given for life?

Answer 42

Life long prophylactic oral antibiotics (phenoxymethylpenicillin - penicllin V)

Question 43

What causes sickling disorders?

Answer 43

Sickling disorders is caused by a point mutation in codon 6 of the B globin gene

Question 44

When the point mutation in codon 6 of the B globulin gene occurs, what does this cause?

Answer 44

This substitutes glutamine to valine producing B s This results in an altered structure of the haemoglobin - HbS (A2B s 2)

Question 45

Describe how sickling disorders occur again? What does HbS cause?

Answer 45

It occurs due to a point mutation in codon 6 of the B globulin gene resulting in the conversion of glutamine to valine This forms the abnromal B globulin Bs This alters the structure of the resulting Hb→ HbS (α2βs2) HbS polymerises if exposed to low oxygen for long periods of times - this causes red cells to deform producing sickle cels

Question 46

WHat does HbS polymerising cause? When do they polymerise? What is the inheritance of this condition?

Answer 46

HbS polymerising occurs when deoxygenated causing red cells to deform producing sickle cells - these cells are fragile and haemolyse and also block small blood vessels - the fragile cell is distored due to the sickling damaging the cell membrane This is an autosomal recessive conditon

Question 47

What population are sickling disorders more common in?

Answer 47

More common in those of African descent

Question 48

What is sickle cell trait?

Answer 48

This is when there is one abnormal and one normal B gene One normal, one abnormal β gene (β/βs) The people here are usually asymptomatic

Question 49

In sickle cell trait * Few clinical features as HbS level too low to polymerise * May sickle in severe hypoxia eg high altitude, under anaesthesia WHat is seen on the blood film? What is the main haemoglobin measured?

Answer 49

Blood film is normal - no sickle cells seen here Main hameoglobin is HbA - HbS<50%

Question 50

Sickle cell anaemia What causes this? What is the main haemoglobin type? What are symptoms?

Answer 50

Caused by two copies of the abnormal B gene (Bs/Bs) resulting in HBSS Majority of blood is HBSS with no HbA Symtpoms include: Painful episodes called sickle cell crises - due to sickling cells getting stuck in small vessels causing tissue infarction, which can be very severe and can last up to a week an increased risk of serious infections & anaemia symptoms

Question 51

What happens to the spleen in sickle cell anaemia?

Answer 51

Chronic haemolysis occurs due to there being increased red cell breakdown Sequestration of sickled RBCs in liver and spleen Hyposplenism due to repeated splenic infarcts

Question 52

What are the precipitants of sickle cell crisis?

Answer 52

Hypxoia Dehydration INfection Cold Fatigue Anything where there is an increase for oxygen

Question 53

What is the importan treatment of sickle cell crisis?

Answer 53

Pain analgesia Hydration Oxygen Antibitoics if thinking infection Blood transfusion if pain is persistent eg chest or neurological symptoms occurring

Question 54

What is given for the long term management of sickle cell anaemia? (ie for the hyposplenism) For the increased red cell turnover demand? What is given if frequent crises?

Answer 54

For the hyposplenism - increases risk of infections therefore lifelong penicllin is given Need folic acid supplementation as there is increased red cell turnover If frequent crises - can gvie hydrxycarbamide to stimulate the production of HbF

Question 55

If people are allergic to penicillin for prophylaxis, what is given? What is the folic acid dose? Stem cell transplantation (the only cure for sickle cell disease) may be considered in children and young people. What age group is this recommended in? What is hydroxycarbamide also known as?

Answer 55

If pen allergic - erythromycin Folic acid - 5mg daily Stem cell transplantation recommended in those aged less than 17 with: Sickle brain disease which does not respond to hydroxycarbamide. Severe sickle cell disease-related complications which have not responded to hydroxycarbamide. Hydroxycarbamide also known as hydroxyureea

Question 56

to diagnose haemaglobinopathies Full blood count - Hb, Red blood cell indices (MCV, MCH etc), Ferritin (Rule out iron), Ethnic origiin What happens to the RCC in IDA and thalassemia? What ethnic origiins are more common for thalassemia and sickle cell anaemia?

Answer 56

Ethnic origin – more common in African patients to have sickle cell anaemia Thalassemia is more common in those of meditteranean to far east origin Red cell count would be raised and ferritin normal (in IDA – red cell count would be low and ferritin would be low)

Question 57

What tests can be used to quantify the haemoglobins present?

Answer 57

HPLC - high performance liquid chromotography or Gel electropheresis (Not really used anymore)

Question 58

High performance liquid chromatography (HPLC) or gel electrophoresis to quantify haemoglobins present Identifies abnormal haemoglobins eg HbS in sickle cell disease What is diagnostic of beta thalassemic trait? What is wrong with HPLC?

Answer 58

Having a raised HbA2 is diagnostic of beta thalassemia trait Beta thal trait - only one parent affected with the abnomral beta gene HPLC is normal in alpha thalassemia trait so need diagnostic testing to confirm Alpha thalassemia - deletions in alpha gene on chromosome 16 (alpha thal trait - only one or two genes deleted - usually asymptomatic)

Question 59

In a normal patient * HbA >80% * HbF When abnormal haemoglobin is identified, DNA-based assays or HPLC are used to confirm the diagnosis and further identify the genotype. On HPLC graphs, different Hb have different peaks Whhy does this person have beta thal trait?

Answer 59

Has a high HbA2 on the HPLC graph which is diagnostic of beta thal trait HbA2 rises in an attempt to help with the decreased HbA

Question 60

WHat does this patient have?

Answer 60

Has a huge peak at HbS - therefore shows the patient has Sickle cell trait MCH is decreased

Question 61

Haemoglobinopathies are genetic disorders affecting globin chain production Rare in the UK but commonest monogenic disorders worldwide Autosomal recessive inheritance Thalassaemias; decreased rate of globin chain synthesis Structural haemoglobin variants eg sickle cell anaemia

• WHat is microcytic usually, but not always due to?
• List causes of both micro and macrocytic anaemias?

Answer 61

Microcytic hypochromic RBCs not always due to iron!

• MICrocytic (Find The Small Cell)
  
  • * Fe2+ deficiency
  • * Thalassemia
  • * Sideroblastic anaemia (porphyrins)
  • * Anaemia of Chronic disease
• MAcrocytic (Can’t Be Fked)
  
  • * Cytotoxic drugs
  • * B12 deficiency
  • * Folate deficiency