HbSC Disease And The Synergistic Effects

Summarise the effects of any combined abnormal haemoglobin defects e.g. HbSC.

The homozygous HbC gene may lead to only a minor hemolytic anemia. However in HbSC disease, the levels of HbS and HbC are the same, but nevertheless, the HbSC disease exhibits an averagely severe phenotype despite being a mixture of both traits of HbS and HbC, both of which do not have any significant pathology. The combination of the two HbS results in serious disease since HbS enhances the pathogenic characteristics of HbS through the dehydration of the SC red cells hence leading to a clinically significant disorder. HbC induces an increase in K:Cl cotransport which in turn leads to loss of K(+) and the intracellular water.

Explain the principle and practice of relevant techniques for the detection and investigation of abnormal hemoglobin variants.

The main test used for the detection of abnormal Hb is screening through electrophoresis. The test is based on the movement of molecules that have been electrically charged under some applied electric field. HbS [β6 Glu>Val], is detected by performing a zone electrophoresis on the cellulose acetate strips (CAE) in a laboratory. The simplicity of this technique has made it one of the most popular methods the screening of Hb abnormalities. The technique basically entails the separation of the some of the Hb molecules at some specific alkaline pH. Under the alkaline condition, all the Hbs variants develop a negative charge and consequently move towards the cathode end. Since HbS usually has an additional positive charge, they move more slowly as compared to the HbA. The electrophoresis of the Hb variants using an acidic pHis more recent technique developed about forty years ago. The technique is more sensitive to the structural modifications as compared to mutated residue.

What are the limitations of the test and what further investigations would overcome there? (100 words) with the investigation of haemoglobin variants. (100 words).

The screening programs for Hb variants have all become well established in most countries over the past few years. However, in spite of this huge amount of knowledge, there are still various problems and limitation in identification. The most common limitation entails the existence of microcytosis with the normal HbA and HbF which is usually because of iron deficiency, α-thalassaemia trait or δβ+-thalassaemia. Anemic iron deficiency can result in a wide range of RBC deficiencies which makes it easily mistaken for some forms of Hb variants. Therefore to diagnose the precise carriers of the Hb variants, a DNA analysis is the most effective method.

Describe the globin chain composition of severe and trait of alpha and beta thalassaemias, BbH disease and HbBarts. (100 words)

The thalassemia syndromes are genetically inherited Hb disorders that are usually characterized by a marked decrease in the accumulation or the total absence in one or more of the globin sub chains of hemoglobin. For the alpha (α)-thalassemias syndrome, the production of the α-globin subunits or chains is decreased or absent. This is usually caused due to the deletion of at least one of the α-globin chains. They are consequently classified according to the number of deletions. In contrast to the (α)-thalassemias, the beta (β)-thalassemias are characterized by a reduction or absence of the β-globin subunits or chains due to mutations. The other thalassemias affect the production of delta (δ)- or gamma (γ)-globin chains.

Summarise the effects of any combined defects of abnormal haemoglobins with imbalanced chain production (e.g. HbS/ Thalassaemia). (100 words)

One of the combined abnormal hemoglobinopathies and the imbalanced chain production syndromes (thalassemias) is the Hb Lepore, a complex disorder of the (δβ)+-Thalassemia group which is characterized by haemotological changes in which the Hb levels are lower with mild changes in the red cells such as microcytosis. HbA is also slightly reduced, however the levels of HbF are characteristically increased by a between 5 percent to twenty percent as well as a mild imbalance in the globin chain. The condition arises from the non-homologous crossing of the δ- and β-globin genes.

Explain the principles and practice of relevant techniques for the detection and investigation of imbalanced chain production. (100words)

The imbalanced chain production syndromes such as the alpha and beta thalassemias can be diagnosed through the evaluation of any incidences of imbalances in the chain production that is reflected by the symptomatic forms of α and β-thalassemias respectively. Usually, the asymptomatic carriers can be identified by the cation exchange high performance liquid chromatography (CE-HPLC) which gives clearer images with superior resolutions. The method basically works by the quantification of the some of the fractions of haemoglobin. Some people can be silent carriers with borderline indices to which a definitive diagnosis is consequently obtained by a combination of the globin chain synthesis and DNA analysis in a laboratory. The analysis determines the various RBC indices.

What are the limitations of the test and further investigations would be required to overcome these? (100words)

The key principle in the diagnosis of these imbalanced chain production syndromes is to detect the presence of any microcytic hypochromia anaemia that is non-iron deficient. In spite of the sensitivity and rapidity of the tests used for diagnosis, sometimes, especially in cases of iron deficient anaemia, the test might bring about false positive results. The best method therefore is to determine the levels of HbA in which most of the carriers of β-thalassaemia have higher levels of HbA accompanied and the alpha thalassemia carriers slightly lower levels than the normal. Both groups of carriers are normally characterized with an increase in the HbF levels as well.

Explain the use of reference values and clinical significance in the interpretation of abnormal results suggesting further testing as required. (100 words)

The HbA and HbF levels can be correctly measured through the application of the CE-HPLC method. However, it is necessary to keep at the back of the mind that the normal value may be slightly different depending on the assay procedures that are used. The beta-thalassemia carriers of either βo or severe β+ are normally characterized by various changes in the red cell indices, the pattern of haemoglobin and the globin chain ratio. The RBC count is normally very high with reduced mean corpuscular volumes (MCV) and mean corpuscular haemoglobin (MCH) at MCV 60-70fl, MCH 19-23pg. The alpha thalassemia carriers on the other hand have an MCH < 25pg.

Describe the relevant internal quality control and external quality assurance procedures associated with the tests. (100 words)

The identification of any of globin chain production imbalances should generally ensure that no carriers elude the detection process. This should be done by carrying out the methodological approaches of identification as specified, by beginning with a primary screening to determine the RBC indices, which is then followed by a secondary screening which entails the analysis of haemoglobin fractions for individuals who are found to have markedly reduced MCV and MCH. Based on the indices and values, regardless of whether presumptive results can be achieved by the analysis of lab results, a DNA analysis still remains the ultimate method for providing precise information.

Learning Reflection (150 words.)

Through this test, I have learnt several important facts about the various haemoglobin pathologies. I have learnt that the conditions comprise of a wide range of genetic and physiological changes, some of which are not very significant while some such as sickle cell, thalassemias and HbSC disease are common and major life threatening diseases with clinically noticeable effects. I have learnt about all these variants, both the abnormal Hb and the globin chain production imbalances, their significant characteristics, symptomatic and asymptomatic forms and more importantly, the clinical diagnosis processes as well as the relevant quality control and assurance procedures to make sure any carriers do not go unidentified. Overall, the lesson on hemoglobinopathy and thalassemias has served as great addition to the knowledge of the various blood defects.

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