Toxoplasmaand reaction time: role of toxoplasmosis in the origin, preservation and geographical distribution of Rh blood group polymorphism

Abstract

The RhD protein which is the RHD gene product and a major component of the Rh blood group system carries the strongest blood group immunogen, the D-antigen. This antigen is absent in a significant minority of the human population (RhD-negatives) due to RHD deletion or alternation. The origin and persistence of this RhD polymorphism is an old evolutionary enigma. Before the advent of modern medicine, the carriers of the rarer allele (e.g. RhD-negative women in the population of RhD-positives or RhD-positive men in the population of RhD-negatives) were at a disadvantage as some of their children (RhD-positive children born to pre-immunized RhD-negative mothers) were at a higher risk of foetal or newborn death or health impairment from haemolytic disease. Therefore, the RhD-polymorphism should be unstable, unless the disadvantage of carriers of the locally less abundant allele is counterbalanced by, for example, higher viability of the heterozygotes. Here we demonstrated for the first time that among Toxoplasma-free subjects the RhD-negative men had faster reaction times than Rh-positive subjects and showed that heterozygous men with both the RhD plus and RhD minus alleles were protected against prolongation of reaction times caused by infection with the common protozoan parasite Toxoplasma gondii. Our results suggest that the balancing selection favouring heterozygotes could explain the origin and stability of the RhD polymorphism. Moreover, an unequal prevalence of toxoplasmosis in different countries could explain pronounced differences in frequencies of RhD-negative phenotype in geographically distinct populations.

Physical and Mental Health Status in Toxoplasma-Infected Women before and 3 Years after They Learn about Their Infection: Manipulation or Side-Effects of Impaired Health?

“…It must be remembered that our population of Rh-positive women represents a mixture of homozygotes and heterozygotes. At the same time, current data suggests that protective effects of Rh factor positivity are fully expressed only in the Rh-positive heterozygotes (Novotná et al, 2008;Flegr, 2016). Therefore, future studies should be performed on DNA genotyped populations.…”

“…The case control study performed on 500 blood donors showed that Toxoplasma-infected Rh-positive heterozygotes showed better psychomotor performancenamely, shorter reaction times-than Toxoplasma-free Rh-positive heterozygotes. At the same time, psychomotor performance of infected Rh-positive homozygotes and especially of infected Rh-negative homozygotes was much poorer than that of corresponding controls (Novotná et al, 2008). It has been shown that toxoplasmosis has various effects on human physiology and some of these effects, such as increase of testosterone (Flegr et al, 2008a,b) or partial immunosuppression (Flegr and StříŽ, 2011), could have a positive impact on human performance and health in certain situations.…”

“…Therefore, future studies should be performed on DNA genotyped populations. The difference between Rh-positive homozygotes and heterozygotes, namely permanent protection against the prolongation of reaction times in heterozygotes and only temporary protection in homozygytes (Novotná et al, 2008), suggests that not only the RhD molecule, but also a product of another gene in a strong genetic linkage with the RHD gene, might be responsible for the observed toxoplasmosisrelated effects of Rh phenotype (Flegel, 2006). For testing such hypothesis, Rh genotype instead of Rh phenotype needs to be monitored in the participants of future studies.…”

“…Rh positive and Rh negative subjects express different sensitivity to the effects of latent toxoplasmosis on psychomotor performance (Flegr et al, 2008c(Flegr et al, , 2012aNovotná et al, 2008) cognitive performance (Flegr et al, 2012a(Flegr et al, , 2013, personality profile (Cattell, 1972;Flegr et al, 2010Flegr et al, , 2012aFlegr et al, , 2013, and mental health (Holub et al, 2011) and also differ in their health status and the incidence of certain disorders Flegr, 2016), but see (Halmin et al, 2017). Many effects of toxoplasmosis are much stronger in Rh negative subjects and some can be detected only in them (Flegr et al, 2009;Kaňková et al, 2010).…”

Pattern of money allocation in experimental games supports the stress hypothesis of gender differences in Toxoplasma gondii-induced behavioural changes

“…the mechanism of the effect of latent toxoplasmosis on human behaviour is unknown; however, we have some indices of deteriorated physical functioning in T. gondiiinfected subjects. these include prolonged simple reaction times (Havlíček et al 2001, Novotná et al 2008, and higher risk of traffic accidents (Flegr et al 2009, Kocazeybek et al 2009) in infected subjects. Deteriorated physical functioning of T. gondii-infected subjects possibly leading to shorter life expectancy could also explain the unexpected phenomenon of decreased seropositivity in the highest age groups in many prevalence studies (e.g.…”