The diagnostic outcomes for different types of anaemia

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Introduction:

This essay focuses on discussing the link amid genetic aberrations that cause anaemia to proliferate and diagnostic outcomes for types of anaemia that exhibit the same principle; where there is a lower than normal blood haemoglobin (Hb) concentration for a patient of a precise gender & age, this is relevant to a lack of mature erythrocytes in vascular flow (Gersten, 2014). It’s significant that anaemia can be qualitative where aberrant Hb is synthesized due to nucleotide substitution or quantitative, where a gene mutation can result in decreased production of ordinary Hb. These categories represent haemoglobinopathies which by meaning are gene mutations that occur in α-/β-globin genes that have the influence of reducing Hb concentration & developing different variants of it (Blann et al, 2010). Sickle-cell anaemia, characterized by sickled erythrocytes, involves hindering Hb’s capacity to effectively acquire & efficiently distribute oxygen satisfactorily to relevant bodily regions (National Health Service, 2014). α-thalassaemia, a deficiency in functional α-globin chains synthesis, is a pathology that’s prevalent in Central Asia; where it exhibits a carrier occurrence of about a fifth (Genetics Home Reference, 2014). Another kind of anaemia, β-Thalassaemia, also entails β-globin chain synthesis reduction but is specifically due to reduced expression β-globin gene (Young, 2010).

Main text:

α-thalassaemia involves up to 4 of the α-globin genes that have undergone alteration. Two normal α-globin genes are inherited from both parents with 16p13.3 as the α-globin gene group loci. In this pathology, genetic deletions occur, rendering at least 1 α-globin gene corrupt, a deletion causes a frame-shift in their amino acid construction, with their protein structures becoming misfolded & incapable of synthesizing normal α-globin (Harteveld and Higgs, 2010). This manifests as an aberrantly low concentration of functional Hb, which is problematic as, interestingly, HbF, HbA and HbA2 (adult Hb variants) require 2 normal α-globins to operate systematically (Blann et al, 2010). There is phenotypic diversity with this anaemia as different gene mutations give rise to different diagnostic results (Kanavakis et al, 2000). If 1 α-globin gene becomes dysfunctional then the patient doesn’t exhibit any greatly deviant symptoms, 2 α-globin genes lost results in α-thalassaemia trait with a placid anaemia type, 3 genes lost results in forming Hb H, reflecting an estimated ¾ reduction in normal α-globins formed with the formation of β4 tetramers and as an outcome severe haemolytic anaemia, excessive number of erythrocytes rupturing (Sheeran and Weekes, 2014). Numerous diagnostic tools should be used to identify specific α-thalassemia subclasses. Initially, a full blood count (FBC) reveals an Hb concentration of 7-10g/dL (normal range: 12-14g/dL), a succeeding blood film would reveal small & pale erythrocytes, indicating it’s microcytic & hypochromic anaemia. If Mean Cell Volume (MCV) & Mean Cell Haemoglobin (MCH) values are below 80fL &27 pg respectively, this would be explained by an excessive quantity of erythrocytes dying prematurely due to a compromise in their Hb’s anatomy, reducing the latter’s affinity for O2 (Cao et al, 2005). Hb electrophoresis would reveal Hb H, an atypical Hb, has migrated on the gel which is diagnostic of Hb H disease. If only two alpha genes are corrupted, then their Hb migration with electrophoresis would be indistinct from normal Hb’s migration as the loss of chains is compensated for by the remaining 2 normal alleles, thus making its detection more challenging. Nevertheless, DNA mutation analysis can be used to identify the 2 faulty α-globin genes & thus be diagnostic of α-thalassaemia trait as it would reveal the point mutations in the gene (Campbell et al, 2009).

With β-thalassaemia there would also be genotypic variability and thus distinct clinical end results for different kinds of this pathology. Even so, a combinatory diagnostic approach would facilitate a more exact diagnosis, as β-thalassaemia involves reduced β-globin chains synthesis owing to point mutations on the β-gene cluster 11p15.5, leading to altered anaemia types (Galanello and Origa, 2010). As this thalassaemia is an autosomal recessive pathology, a full blood count would show no deviations for a silent carrier with 1 normal β-globin gene, as 1 β-globin gene can still maintain satisfactory Hb amounts. Contrastingly, with 2 altered genes, which is recognized as β-thalassaemia major, the patient would demonstrate Hb concentration of 3-8g/dL, an MCV below 80fL and MCH value below 27pg. Further, an erythrocyte count below 4.5x1012/L and 3.9x1012/L for males and females respectively and a reticulocyte count above the normal range of 50-150x109/L would also be seen (National Institutes of Health, 2012). It’s key that the low erythrocyte count is owed to excessive haemolysis as both β-globin genes are mutated which gives rise to total inhibition of β-globin gene expression. This disturbs the α:β equilibrium as the α-globin chains would comparably be in excess, having the consequence of rendering it unstable and hindering it’s function to load oxygen and encourages the production of inclusion complexes in erythrocyte precursor molecules. This clarifies why undersized pale microcytes are apparent in the blood film, as the Hb’s O2-affinity is significantly reduced, making the erythrocytes appear discoloured (Young, 2010). The elevated reticulocyte count reflects the increased erythropoietic behaviour of the bone marrow as an attempt to compensate for the erythrocytes dying prematurely by releasing reticulocytes into the bloodstream earlier to support a more rapid maturation (Bunyaratvej et al, 1994). β-thalassaemia sufferers display a varied array of phenotypes & thus mere reliance on clinical symptoms wouldn’t precisely deduce the β-thalassaemia type, highlighting the importance of conducting other diagnostic tests to facilitate precise diagnostic determination (Thein, 2004). This is resolved by Hb electrophoresis which confirms the absence of HbA which requires β-globin chains to function but this requisite isn’t met due to β-globin gene inactivation (Thein, 2008).

Sickle-cell anaemia (SCA) requires 2 mutant β-globin alleles to manifest as it’s autosomal recessive. It’s identification with a full blood count reveals an Hb concentration of 6-9g/dL with an aberrantly high reticulocyte count (Ben-Ezra and Goel, 2001). These results are due to nucleotide substitution of adenine to thymine in the 6th codon of the β-globin gene, resultantly encoding for valine, forming α2β2 tetramers which, when oxygen saturation’s below 85%, are unstable. This encourages it’s polymerisation which results in it creating elongated complexes – rendering erythrocytes sickled which is confirmed by the sickled cells’ presence in blood film (Young, 2010). Such fragility encourages excessive haemolysis as their lifespan lessens, reducing Hb concentration. This would also justify the presence of splenomegaly (spleen distension) & jaundice (yellow skin tone) as the spleen’s involved in non-functional erythrocytes’ removal & thus functions excessively. Jaundice arises as excessive bilirubin is released from haemolysed erythrocytes (Sergeant, 2001). If the patient’s carrying 2 mutant alleles, Hb electrophoresis would reveal no HbA present with HbS levels >80%, this confirms the diagnosis of SCA. Significantly, a carrier of 1 mutant allele would show less HbA migrated but still show a comparatively lower concentration of HbS present which is diagnostic of the sickle-cell trait.

HbA’s absence is apparent by knowing that HbA’s based on 2 α-globin & 2 β-globin chains, the fact that sickle-cell disease is an autosomal recessive condition indicates that only 1 normal β-globin allele can still maintain a sufficient albeit slightly lower quantity of HbA by still encoding for β-globin chains, whereas 2 mutant alleles prevents HbA’s production as no β-globin chains are synthesized, justifying the electrophoresis result. This highlights SCA’s genotypic diversity & that this mediates indications to arise which are unique in some cases but in other cases requires further testing as some symptoms tend to be generic amongst all anaemia variations. For instance, splenomegaly is due to increased erythrocyte removal and would therefore occur in other haemolytic anaemia types, further stressing the importance of conducting other practical tests to differentiate among dissimilar types that occur due to different mutational events of the globin genes concerned.

Conclusion

Alpha & beta globin gene alterations highlight their influence in causing anaemia which requires use of diagnostic tools to identify haemoglobinopathies. Whilst different kinds of anaemia have distinct genetic mutations, patients may exhibit similar clinical qualities that are observed in other anaemic variations and so demands that different mutations and their loci be determined and therefore demonstrates the crucial significance of knowing what occurs genetically to understand the diagnostic outcomes that correspond to a range of anaemia.

Reference list:

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Galanello, R. and Origa, R. (2010). Beta-thalassemia. Orphanet Journal of Rare Diseases. May 5 (11), 1-15. [online] Available from: BioMed Central Ltd. <http://www.ojrd.com/content/5/1/11> [Accessed 05 October 2014].

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Sheeran, C. and Weekes, K. (2014). Complications of Hb H disease in adulthood. British Journal of Haematology. Oct 167 (1), 136-139. [online] Available from: Wiley Online Library. <http://onlinelibrary.wiley.com/doi/10.1111/bjh.12932/full> [Accessed 06 October 2014].

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