Evidence for associations between the purinergic receptor P2X(7) (P2RX7) and toxoplasmosis

Abstract

Congenital Toxoplasma gondii infection can result in intracranial calcification, hydrocephalus and retinochoroiditis. Acquired infection is commonly associated with ocular disease. Pathology is characterized by strong proinflammatory responses. Ligation of ATP by purinergic receptor P2X(7), encoded by P2RX7, stimulates proinflammatory cytokines and can lead directly to killing of intracellular pathogens. To determine whether P2X(7) has a role in susceptibility to congenital toxoplasmosis, we examined polymorphisms at P2RX7 in 149 child/parent trios from North America. We found association (FBAT Z-scores +/-2.429; P=0.015) between the derived C(+)G(-) allele (f=0.68; OR=2.06; 95% CI: 1.14-3.75) at single-nucleotide polymorphism (SNP) rs1718119 (1068T>C; Thr-348-Ala), and a second synonymous variant rs1621388 in linkage disequilibrium with it, and clinical signs of disease per se. Analysis of clinical subgroups showed no association with hydrocephalus, with effect sizes for associations with retinal disease and brain calcifications enhanced (OR=3.0-4.25; 0.004<P<0.009) when hydrocephalus was removed from the analysis. Association with toxoplasmic retinochoroiditis was replicated (FBAT Z-scores +/-3.089; P=0.002) in a small family-based study (60 families; 68 affected offspring) of acquired infection in Brazil, where the ancestral T(+) allele (f=0.296) at SNP rs1718119 was strongly protective (OR=0.27; 95% CI: 0.09-0.80).

Figure 1

Haploview analysis for D’ and r² pairwise measures of LD between P2RX7 SNPs in unrelated family founders for (a) NCCCTS and (b) Brazil. D’ values and confidence levels (LOD) are represented as bright red for D’=1, LOD≥2; blue for D’=1, LOD<2; white for D’<1, LOD<2. r² values are represent as black for r²=1, white for r²=0, with intermediate values for 0<r²<1 indicated by shades of grey. The numbers within the squares represent the D’ or r² scores for pairwise LD.