Brain Behav Immun 2001 Dec

impressive number of similarities.  Both are chronic, relapsing diseases of

unknown etiology.  Both became prominent in the early 19th century and have

prevalences of approximately 1% in North America and Europe.  Both run in

families, have pairwise concordance rates of approximately 30% among monozygotic

twins, and are more common among individuals born in urban areas.  For both

diseases, studies have reported greater exposure to cats in childhood than in

controls.  Both diseases have been associated with similar class II HLA

antigens.  Both have also been suspected of having infectious etiology,

with similar agents–retroviruses, herpesviruses including EBV, and Toxoplasma

gondii–having been associated in some cases.  Since there is also a

well-documented inverse correlation between these two diseases, it is possible

that they share a common infectious and/or immune etiology and that once a