**Section 3**

**Neuro-Psychiatric Epidemiology** 

110 Epidemiology Insights

Zhang, K.; McClure, J.A.; Elsayed, S.; Conly, J.M. (2009) Novel staphylococcal cassette

ISSN 0066-4804

chromosome *mec* type, tentatively designated type VIII, harboring class A *mec* and type 4 *ccr* gene complexes in a Canadian epidemic strain of methicillin-resistant *Staphylococcus aureus*. *Antimicrobial Agents and Chemotherapy*. Vol. 53, pp. 531-540.

**7** 

*Japan* 

(Engels)

**Impact of Epidemiology on Molecular** 

**Genetics of Schizophrenia** 

Takeo Yoshikawa3 and Tomoe Ichikawa2 *1Ibaraki Prefectural Medical Center of Psychiatry 2Tokyo Metropolitan Institute of Medical Science* 

*3RIKEN Brain Science Institute* 

Nagafumi Doi1, Yoko Hoshi2, Masanari Itokawa2,

'To grasp the full meaning of the *obvious* is a better basis for the understanding than the confused knowledge of the *obscure*.'

Schizophrenia is a common deleterious psychosis that begins typically in late adolescence or early adulthood (Gottesman, 1991; Jablensky, 1995). Although it has a strong genetic component in its etiology, no susceptibility genes conferring a large proportion of heritability have been identified (Allen et al., 2008; Need et al, 2009). Results of association studies including genome-wide scans have been inconsistent, and schizophrenia-associated genes including copy number variations differ across populations or even across individuals of a same ethnicity (Allen et al., 2008; Xu et al., 2008; Need et al, 2009). Thus, situation of molecular genetics of schizophrenia has become rather perplexing just contrary to our expectation.

In this chapter, we describe the consistent major epidemiological findings of schizophrenia, and show how these evident macroscopic aspects shed light to the confused microscopic aspects of

We describe here three epidemiological facts of schizophrenia – high prevalence, high heritability and low reproductive fitness. These properties form a Devil's triangle; any combination of the two tends to exclude the third, and in this triangle most diseases vanish except for schizophrenia, suggesting that schizophrenia has a unique etiological basis

Substantial evidence of epidemiology shows that schizophrenia crosses all cultures and tribes in different continents at a relatively high prevalence (approximately 0.7%; 95%

schizophrenia genetics today, proposing a new hypothesis for this puzzling disorder.

**2. Devil's triangle of human genetics – Epidemiological facts of** 

**1. Introduction** 

**schizophrenia** 

among the many human diseases.

**2.1 Schizophrenia as a common disease** 
