Van Rijn et al (Reference Van Rijn, Aleman and Swaab2006) concluded that their findings suggested a link between an X chromosomal abnormality and liability to schizophrenia which might be useful in the search for the genetic aetiology. Moreover they stated that a crucial role for X chromosome abnormalities in this context has been proposed by Lishman (Reference Lishman and Lishman1998). In 1966 Hambert described a group of 75 XXY men, of whom 17 had hallucinations, 21 paranoid ideas, 9 ‘megalomanic ideas’ and 5 ‘short periods of mania-like disorder’. Penrose (Reference Penrose1966) claimed that ‘the effects of sex chromosomal disorders are more noticeable in relation to alterations in character and stability than to intellectual loss. Olanders (Reference Olanders1975), working in the same research group as Hambert and Penrose, reported 16 women with schizophrenia among 31 with triple X syndrome. Olanders’ own psychiatric investigation of these women revealed many with paranoid symptoms who did not meet his strict criteria for schizophrenia. He described a paranoid syndrome in 8, hallucinations in 4, confusion in 3 and catatonic symptoms in 2.

Van Rijn et al discuss the relationship between an extra X chromosome and psychosis through the ‘decreased cerebral lateralisation’ hypothesis. Netley & Rovet (Reference Netley and Rovet1982) reviewed data which point to diminished cerebral cell numbers owing to lower mitotic rates which also result in the lower dermal ridge counts. I think that a lower cerebral cell number could give rise to decreased cerebral lateralisation, but this needs further investigation.

In my opinion, Van Rijn et al present no new data but have rediscovered what was known for a long time.