It is known that a normal human chromosome set consists of 46 chromosomes, including 22 pairs of autosomes and one pair of sex chromosomes XX or XY. One form of abnormality of the genotype of sex chromosomes is karyotype 47, XYY. This is the least studied and attention-grabbing deviation.
Syndrome XYY is a hereditary disease associated with the presence of extra Y-chromosome in male karyotype. It is the result of non-disjunction of sex chromosomes during gametogenesis. About one among thousand live-born boys has this syndrome (Nielsen, 1969).
Until recently, the role of genetic factors as the cause of abnormal and criminal behavior did not attach much importance. In 1961, the first man with an extra Y-chromosome was discovered. (The chromosomes in the cells of his blood were subjected to investigation, since his son had Down's syndrome). Scientists were interested in the question whether abnormalities of sex chromosome predispose to abnormal behavior of individuals. This problem attracted attention of professionals in different countries after 1965, when Dr. Patricia Jacobs and colleagues from Edinburgh reported the results of their research. They were among the first, who noticed that an unusual number of chromosomes was not typical for the majority of the population, but for persons who were in custody. Moreover, they gave a description of the syndrome XYY, which was characterized by signs of excessive aggression, sudden outbursts of violence, and mental retardation. Although the results of subsequent studies did not always coincide, most of them confirmed the findings of the initial study that XYY chromosome type was more common among criminals than among representatives of other groups. The scientists studied chromosome set of mentally retarded male patients and patients committed various crimes to determine whether the presence of excess Y-chromosome was connected with an unusually aggressive behavior. It was established that of 196 men 6.1% had an abnormal chromosome set, 3.6% had an extra Y chromosome, and thus, their set of sex chromosomes was XYY (Shihab, 2012).
The most common sign of Jacob’s syndrome XYY is a high stature. According to British reports, among criminals above 184 cm, approximately every fourth has this set of chromosomes. However, this feature is not absolute, as there are also men with karyotype 47, XYY that have an average height. Some patients have the mild expressed eunuchoid features of the constitution and dysplastic symptoms: abnormal structure of teeth, an increase of the lower jaw, abnormal bite, deviation of knee and elbow joints, cryptorchidism, genital dysplasia, and poor fine motor skills. Some patients have increasing levels of androgens and luteinizing hormone. Sexual function is not compromised, but there are cases of underdevelopment of the testicles, infertility or reduced fertility. The presence of the extra Y- chromosome cannot be accompanied by clinical pathology, but, undoubtedly, it is correlated with both intellectual underdevelopment, and with the emotional and volitional impairment. 30-40% of men with the extra Y-chromosome have borderline or mild mental retardation, complicated emotional and volitional disorders as dysphoria, hostility, and malice towards others, impulsivity, explosiveness. The child's challenging behavior has a tendency to bring damage. He reveals sudden symptoms of irritability in any failure, certainly stubborn desire to get into dangerous places (usually all these are manifested in the child to four years). However, there is no need to be psychologists to understand that there are many children whose behavior is not different from that described above, although the chromosome set is completely normal (Nielsen, 1969).
Education of mentally retarded patients in a special school provides a set of medical and educational activities aimed mainly at correcting psychopathological traits. Involving patients in the labor force (working on the school grounds and labor workshops) and their early professional orientation contribute to social inclusion. Adult man with the karyotype 47, XYY needs psychological support and genetic consultation (Nielsen, 1969).