Variants in the non-coding region of the TLR2 gene associated with infectious subphenotypes in pediatric sickle cell anemia
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Sickle cell anemia (SCA) is characterized by chronic hemolysis, severe vasoocclusive crises (VOCs), and recurrent often severe infections. A cohort of 95 SCA pediatric patients was the background for genotype-to-phenotype association of the patient’s infectious disease phenotype and three non-coding polymorphic regions of the TLR2 gene, the −196 to −174 indel, SNP rs4696480, and a (GT)n short tandem repeat. The infectious subphenotypes included (A) recurrent respiratory infections and (B) severe bacterial infection at least once during the patient’s follow-up. The absence of the haplotype [Del]-T-[n ≥ 17] (Hap7) in homozygocity protected against subphenotype (B), in a statistically significant association, resisting correction for multiple testing. For the individual loci, the same association tendencies were observed as in the haplotype, including a deleterious association between the SNP rs4696480 T allele and subphenotype (A), whereas the A/A genotype was protective, and a deleterious effect of the A/T genotype with subphenotype (B), as well as including the protective effect of −196 to −174 insert (Ins) and deleterious effect of the deletion (Del) in homozygocity, against subphenotype (B). Moreover, a reduction in the incidence rate of severe bacterial infection was associated to a rise in the hemolytic score, fetal hemoglobin levels (prior to hydroxyurea treatment), and 3.7-kb alpha-thalassemia. Interestingly, differences between the effects of the two latter covariables favoring a reduction in the incidence rate of subphenotype (B) contrast with a resulting increase in relation to subphenotype (A). These results could have practical implications in health care strategies to lower the morbidity and mortality of SCA patients.
KeywordsSickle cell anemia TLR2 Genetic variants Viral and bacterial infection Hemolytic component Genotype-to-phenotype association
We are grateful to the patients and their families. We also thank Dominique Labie for having suggested this topic of research. We thank INSA’s “Unidade de Tecnologia e Inovacão” as well as Andreia Coelho and Emanuel Ferreira for their technical support. We thank Eric David Bosne for the insight in PCA. We also thank Audrey V. Grant, Baltazar Nunes, Paula Faustino, and Vera C.M. David for their helpful suggestions in the elaboration of the study. This study was carried out with financial support from FCT/MEC through national funds and co-financed by FEDER, under the Partnership Agreement PT2020, in the project with reference UIDMULTI/00211/2013, and was partially funded by FCT grants PIC/IC/83084/2007 and the Centro de Investigação em Genética Molecular Humana (CIGMH).
Conceived and designed the experiments: S David, A Dias, A Morais, J Lavinha. Suggested methodologies: S David, A Dias, A Morais, A Sakuntabhai, J Lavinha. Genotyped: S David. Reorganized the database: S David. Analyzed the data: S David, P Aguiar. Carried out the investigation: S David. Provided the resources: A Dias, A Morais, J Lavinha. Wrote the paper: S David. Reviewed the paper: P Aguiar, J Lavinha, A Sakuntabhai. All authors approved the final version of the paper.
Compliance with ethical standards
Conflict of interests
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
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