Jacobs syndrome, or XYY syndrome, or disomy of the Y chromosome is a heterosomic aneuploidy, that is a karyotypic anomaly, in which, besides the X and Y chromosomes typical of the normal human male complement, a supernumerary Y chromosome is present. This polysomy is due to a non-disjunction during the second meiotic division in male gametogenesis.

Despite the slender genetic contribution of the Y chromosome, a number of characteristics have been identified in carriers of the aneuploidy. Although not particularly homogeneous, they do occur with a significantly higher frequency than that with which the same traits are found in the general population. Such individuals are also called supermales and may often be taller than 180 cm (average 188 cm) and show mild intellectual disability.^[1][2][3] They may have large teeth or teeth with large roots,^[4][5] may have Marfan-like vascular problems ^[6][7] and an association with defects of embryonic lateralisation has also been suggested.^[8]

Contrary to what was supposed in the past (they were previously considered particularly tall), testosterone levels are normal.

The frequency with which this ploidy occurs is 1-5/10000 males ^[9].

A historical error

   This condition is known for its history, since at the birth of the criminological sciences, on the wave of Lombrosian and physiognomic theories and of social Darwinism, attempts were made to find genetic causes of criminal behaviour.

It is often cited in statistics as an example of statistical error, committed when the study sample is not adequate: the supposed link between XYY and criminality was in fact taken as certain solely on the basis of studies carried out inside prisons, whereas by using a more adequate sample it was possible to observe that the syndrome is in reality spread evenly through the population, with no difference of class, occupation, religion or ethnic background. The presumed criminal tendency of the carriers of this anomaly is used as a plot device in Dario Argento's film The Cat o' Nine Tails. Individuals carrying 47,XYY syndrome are the 25 inmates of the Fiorina "Fury" 161 penal colony in the science-fiction film Alien³.

 

The discovery of an association between nutritional deficiencies and psychiatric disorders goes back to 1958, when the Canadian physicians A. N. Payza and D. G. Irvine, of the research group led by Dr Abram Hoffer, found an unknown mauve-coloured substance both in the urine of healthy volunteer patients who had been given the psychedelic drug LSD and in the urine of psychiatric patients who had not been given that drug. This unknown substance was called the “mauve factor”.

Dr Hoffer discovered that high levels of the mauve factor were frequently found in the urine of schizophrenic patients, but also in depressed and anxious patients, in children with language and behavioural disorders and in alcoholics. High levels of the mauve factor, by contrast, were rarely found in non-psychiatric patients. Hoffer named this condition “malvaria”, showing that in
schizophrenic patients taking high doses of vitamin B3 caused the mauve factor to disappear from the urine, with a
remission of the symptoms associated with the illness. If the intake of vitamin B3 was interrupted, the mauve factor reappeared in the urine, and with it the symptoms of schizophrenia. Later studies have confirmed the presence of the mauve factor in patients affected by many other kinds of disorder of the cognitive, affective and behavioural sphere.