SICKLE CELL ANEMIA: GENETIC DETERMINANTS OF DISEASE SEVERITY IN CHILDREN
FROM ANGOLA
Catarina Ginete1, Mariana Delgadinho1, Brígida Santos2,3 and Miguel Brito1,3
(
1)H&TRC Health and Technology Research Center. Escola Superior de Tecnologia da Saúde de Lisboa,
Instituto Politécnico de Lisboa, Lisboa, Portugal
(2)Hospital Pediátrico David Bernardino (HPDB), Luanda, Angola, (3)CISA Centro de Investigação em
Saúde de Angola, Caxito, Bengo, Angola
I
ntroduction: Sickle cell anemia (SCA), an inherited life-threatening monogenic disease,
affects over 300,000 newborns world-wide every year, being particularly prevalent in sub-
Saharan Africa. This disease results from a single nucleotide substitution in the 6th codon of
the HBB gene, causing an amino acid substitution from glutamic acid to valine, which affects
the hemoglobin behavior in deoxygenated conditions. Red blood cells tend to be denser and
less deformable, blood viscosity increases, and as a result, these patients are predisposed to
vaso-occlusion and ischemic events, hemolysis and inflammation.
Although being a monogenic disease, the clinical presentation of these patients tends to be
very heterogeneous, probably due to the presence of other polymorphisms. Genetic analysis
of the HBB gene cluster has revealed five distinct haplotypes: Senegal (SEN), Benin (BEN),
Bantu or Central African Republic (CAR), Cameroon (CAM) and Arab-Indian (AI). In addition to
the HBB cluster, other genes and loci have been described to significantly impact disease
severity by altering HbF expression, like BCL11A and HBS1L-MYB intergenic region.
The aim of this study was to assess the association between SNPs in genes associated with
SCA and disease severity, by sequencing HBB cluster, BCL11A, HMIP 2b, HBS1L-MYB intergenic
region, KLF1, Fox3 and ZBTB7A regions.
Methodology: A cohort of 192 Angolan children, between the ages of 3 and 12, from Hospital
Pediátrico David Bernardino and Hospital Geral do Bengo, were recruited and followed up for
this study. Clinical anamnesis and physical examinations were performed prior to blood
collection for the determination of hematological and biochemical parameters. After DNA
extraction, paired-end sequencing was accomplished using the Illumina NextSeq 550.
Haplotype classification was based on four previously described SNPs from HBE1 (rs3834466),
HBG1 (rs28440105) and HBBP1 (rs10128556) genes and a SNP located in the intergenic region
between HBBP1 and HBD genes (rs968857). The correlation of clinical variables with the
different haplotypes and other polymorphisms was assessed with SPSS version 26 package.
Results: We found that the most prevalent haplotype was the CAR/CAR, detected in 91.7%,
followed by the CAR/BEN in 5.7%. Surprisingly, all the patients had at least one CAR allele and
the ANOVA tests showed significant differences in several parameters: total hemoglobin, fetal
hemoglobin, gamma chains proportion and red blood cell count.
Considerable differences in total hemoglobin and fetal hemoglobin were also reported among
other genotypes. Some of the identified polymorphisms were associated with variables that
reflect anaemia severity, namely stroke and hemolysis.
Moreover, the proportion of gamma chains was influenced by a particular SNP in the BGLT3
gene a long noncoding RNA locus.
Discussion: The current findings emphasize the importance that personalized medicine would
have if applied to SCA patient care.