|'I' before the 'E' except after 'C'.|
That was the rather peculiar question posed and partially answered in the paper by Fuller Torrey and colleagues . They concluded that "cat ownership in childhood is significantly more common in families in which the child later becomes seriously mentally ill."
For those new to this topic, it might sound rather strange that cat ownership in childhood might elevate the risk of mental illness. But just before you smirk and click away, please read on a little further.
Previous research had hinted that cat ownership during childhood might be one of a number of factors linked to the presentation of psychosis  based on findings from some of the authorship group as part of their feline zoonosis theory of schizophrenia . Zoonotic diseases, by the way, are diseases that can be transmitted from animals to people. The idea intersecting with a growing evidence base specifically suggesting that Toxoplasma gondii, a protozoan that finds a home in some cats and is shed in cat poo(p), might be linked to quite a few cases of schizophrenia (see here) following the potential crossing of the gondii from cats to humans.
I've covered the possibility of a link between T. gondii and cases of schizophrenia quite a few times on this blog (see here and see here for example). I have to say that the evidence is getting pretty strong for the possibility of a link between T. gondii exposure and risk of [some] schizophrenia with the requirement for quite a bit more investigation into the possible mechanisms involved. The idea that T. gondii, once it has found a home in someone, might be able so extremely affect a person's behaviour is also not as outlandish as it may first sound. 'Rats attracted to cats' was a post a few years back (see here) demonstrating the potential of T. gondii to affect animal behaviour and drive rats to become sexually attracted to cat urine followed by an almost certain death to the rat but continued survival for the parasite. Human are slightly more complicated creatures than rats but the idea of T. gondii leading to/causative of other behaviours has been entertained in the research literature .
Before anyone gets any ideas that I'm somehow 'anti-cat' based on this and other posts, I'm not. Whilst myself allergic to cats, I'm as sold on the cuteness of the Lego movie 'believe' poster as the next person. What however this line of scientific investigation does suggest is that one should always be a little bit cautious about the potential risks specifically associated with cat ownership. How, as well as being relevant to pregnant women, young family members should know about the potential issues of T. gondii when it comes to keeping a cat and in particular, keeping clear of places they poo(p). Some common sense guidance has been recently published with this in mind (see here).
Music: Arctic Monkeys - Mardy Bum (spoken in my best Sheffield accent).
 Fuller Torrey E. et al. Is childhood cat ownership a risk factor for schizophrenia later in life? Schizophrenia Research. 2015. 18 April.
 Fuller Torrey E. et al. The antecedents of psychoses: a case-control study of selected risk factors. Schizophr Res. 2000 Nov 30;46(1):17-23.
 Fuller Torrey E. & Yolken RH. Could schizophrenia be a viral zoonosis transmitted from house cats? Schizophr Bull. 1995;21(2):167-71.
 Ling VJ. et al. Toxoplasma gondii Seropositivity and Suicide rates in Women. The Journal of nervous and mental disease. 2011;199(7):440-444.
Fuller Torrey, E., Simmons, W., & Yolken, R. (2015). Is childhood cat ownership a risk factor for schizophrenia later in life? Schizophrenia Research DOI: 10.1016/j.schres.2015.03.036