Toxoplasma gondii seropositivity as a risk factor for epilepsy: A discordant monozygotic twin study

Toxoplasma gondii (T. gondii) seropositivity has been reported to have up to a five-fold increased risk for epilepsy. However, substantial heterogeneity in methodology exists across these studies. Furthermore, other studies failed to replicate an association between T. gondii seropositivity and epilepsy. To address these inconsistencies, we investigated this issue in monozygotic (MZ) twin pairs discordant for epilepsy, a method that controls for age, sex and genetic factors.

We analyzed 32 MZ twin pairs who are discordant for epilepsy, comparing rates of T. gondii seropositivity (IgG) between affected and unaffected twins. The odds ratio for T. gondii seropositivity in affected twins compared to their unaffected co-twins was calculated using McNemar's chi-squared paired proportion test. Factors associated with T. gondii seropositivity were assessed using Fisher's exact test and Welch's t-test, as appropriate.

The frequency of seropositivity in affected twins compared to their unaffected co-twins did not differ (odds ratio of 1.67 [95 % CI: 0.39-6.97], p = 0.72), indicating no significant association between T. gondii seropositivity and epilepsy in this cohort. Age at testing was associated with T. gondii seropositivity, with individuals found to be seropositive being older than those who were seronegative [mean age at testing (SD) 59.1 years (12.6) vs 47.7 years (14.3), p = 0.03].

In our cohort of MZ twins discordant for epilepsy, we found no evidence for an association between T. gondii seropositivity and epilepsy. Larger carefully controlled studies are warranted.