Evidence of genetic susceptibility to infectious mononucleosis: a twin study

Infectious mononucleosis is a clinical manifestation of primary Epstein-Barr virus infection. It is unknown whether genetic factors contribute to risk. To assess heritability, we compared disease concordance in monozygotic to dizygotic twin pairs from the population-based California Twin Program and assessed the risk to initially unaffected co-twins. One member of 611 and both members of 58 twin pairs reported a history of infectious mononucleosis. Pairwise concordance in monozygotic and dizygotic pairs was respectively 12.1% [standard error (S. E.)=1.9%] and 6.1% (S.E.=1.2%). The relative risk (hazard ratio) of monozygotic compared to dizygotic unaffected co-twins of cases was 1.9 [95% confidence interval (CI) 1.1-3.4, P=0.03], over the follow-up period. When the analysis was restricted to same-sex twin pairs, that estimate was 2.5 (95% CI 1.2-5.3, P=0.02). The results are compatible with a heritable contribution to the risk of infectious mononucleosis.