As P. falciparum is haploid in humans, isolates containing both resa2 T1526C mutant and wild alleles corresponded to multiclonal isolates. Multilocus genotyping of the Senegalese isolates showed quite a large genetic diversity, and importantly outlined that most patients (SM and UM) were infected by at least two distinct clones . In the present study some isolates (one UM case Senegal, three SM cases and three UM cases in Benin) harboured both wild and mutant resa2 alleles. As the proportion of each allele within those mixed isolates was unknown, it appeared difficult to correlate the severity of the clinical access with the presence of resa2 mutant for those isolates. Indeed, the analysis including those mixed isolates did not show an association of the presence of the mutant allele and severity of malaria. Conversely, such an association was found in the analysis excluding the mixed isolates. In addition, an association of the presence of the mutant allele and parasitaemia > 4% was found in the group of Beninese children.
To gain statistical power, data from Beninese and Senegalese groups were combined to assess the association between mutant allele and severity of malaria. This association, observed for the combined series (n = 154), was not significant for each group alone probably due to a lack of power, but a trend towards this association was found for each group.
About 14% of isolates obtained from Senegal and Benin harboured mutant T1526C parasites. Sequencing of resa2 cDNAs showed that the mutation T1526C affects an internal stop codon and restores a unique open reading frame. Thus, all mutant parasites theoretically have the ability to encode a full-length protein. RESA2 protein as RESA1 has a PEXEL motif and is member of the pHISTb (Plasmodium helical interspersed subtelomeric family) protein family  suggesting that as its sister protein RESA1, it could be secreted out of the parasite and contribute in vivo to remodelling the host cell and possibly the erythrocyte membrane so as to favour high-density infections.
In multivariate analysis, parasitaemia >4%, appeared as a factor associated with the presence of mutant T1526C parasites in the group of Beninese children. It should be stressed that parasitaemia >4% is by itself a criterion, including the case in the severe category of malaria attack. Thus, it is not surprising that the presence of mutant T1526C parasites was associated with both parasitaemia >4% and SM. Indeed, it has been reported that P. falciparum isolates from patients with severe malaria had higher multiplication rates in vitro than those from uncomplicated malaria . A similar observation was obtained in the series from Benin using short-term, 72-hour in vitro culture growth assay. Moreover, five out of six parasites harbouring the T1526C mutation, and collected from patients who had not taken anti-malarial prophylaxis, were able to multiply in culture, a prevalence far above the one observed for parasites carrying the wild allele. A rapid multiplication rate leading to high parasite density before an effective protective response is attained may contribute to severity [27–29].
Most severe cases of the series (43 of 51 in Benin, 33 of 39 in Senegal) were not due to parasites harbouring the T1526C mutation. There is no simple one-to-one correlation between the clinical syndrome and the pathogenic processes involved in SM, probably reflecting the contribution of multiple host and parasite factors to malaria pathogenesis. Yet the T1526C mutation is one of the first parasite SNPs associated with SM. Further work is needed to understand how the RESA2 protein contributes to pathogenesis and whether or not it fulfils a role similar to RESA1 in providing the parasites with a better fitness and survival under febrile conditions.