To relate clinical phenotype to genotype and underlying inflammation among a cohort of thalassaemia homozygotes

Abstract

In a multitude of human diseases, excessive inflammation poses detrimental consequences. Inflammation entails both paracrine and autocrine responses together with a variety of genetic susceptibility factors brought about by many genes and endogenous mediators (Kaminska, 2005). In the Maltese population, β-thalassaemia is the most frequented single gene disorder. Naturally, an inclined interest in research on βthalassaemia, over the span of 25 years, has led to an accumulation of prospective clinical data.

This study evolves around the hypothesis by Felice et al (1991), being that, the medullary inflammation found in β+-thalassaemia patients may solely restrict hydroxyurea’s (HU) ameliorating effects. The supposed inflammation could also be the culprit in making the bone marrow more susceptible to the myelotoxic effects of the drug, limiting erythropoiesis and HbF synthesis. In theory, pharmacological HbF induction, especially in patients with relatively mild β-thalassaemia could serve to reduce or even eliminate the incessant frequent transfusions. Nonetheless, as shown in a local trial by Galea (2005), low-dose HU therapy did not lead to favourable results in comparison to the affirmative results reported in sickle cell disease patients (SCD). In previous literature, Vella (2018) performed panel exome sequencing, particularly in search for inflammation-related gene variants, that could have a role in the inflammatory process in patients with β-thalassemia.

Out of this data, the three genes: MAP2K3, TLR2 and CFB were undertaken in this research project. To test the hypothesis, the mutations in all three genes were analysed from whole exome sequencing. The gene expression of the three loci was also measured with quantitative RT-PCR and normalised to a non-transfusion dependent β-thalassaemia major patient by the comparative CT method. The single nucleotide variants (SNVs) and different levels of gene expression values obtained were than compared to white blood cell counts, C-reactive protein which is an inflammatory marker and the clinical severity index (CSI) of the patient, to determine if there was any correlation between these parameters. Conclusively, the evaluated genes and deleterious variants that could undermine inflammation in the context of β-thalassaemia provided no direct correlation, prompting the need for further research. Future work could include transcriptome global analysis.