XYY syndrome is a genetic condition where an extra copy of a Y chromosome is present in each of the cell of human male, resulting in 47 chromosomes instead of 46.
Tall stature, macrocephaly, macroorchidism, hypotonia, hypertelorism, and tremor are the common features of the XYY phenotype. There is no gross difference of physical phenotypic features whether the syndrome is diagnosed prenatally or postnatally. However, prenatal diagnosis of this syndrome is associated with the development of higher cognitive function.
Features of XYY syndrome include:
Two tests may be used to diagnose XYY Syndrome:
Several brain malformations in the form of posterior fossa anomalies, such as cerebellar dysplasia or hypoplasia, cerebellar cysts, vermis dysgenesis or hypoplasia, mega cistern magna were previously thought to be associated with sex chromosome anomalies. It was suggested that presence of an extra copy of sex chromosome may affect prenatal brain development. XYY syndrome, with an extra copy of the Y chromosome, thus may have a chance to develop those anomalies. Brain radiological imaging of males with XYY syndrome could be utilized to determine whether the existence of such brain abnormalities is an incidental or part of the spectrum of XYY syndrome. A deeper understanding is needed through further research for correlating the effect of an extra chromosome with the pathophysiology of the development of behavioral and physical disorders in affected individuals.
Treatment options are mainly supportive as it is not possible to alter the basic pathology of 47, XYY syndrome:
XYY syndrome is occasionally diagnosed in boys of 11 and 12 years of age, referred actually for attention deficit hyperactivity disorder (ADHD). Abnormally high stature (patients were above 97.5% height for age), typical muscle consistency and persistence of tremor among the boys points towards a need for chromosomal analysis. A team consisting of a neuropsychologist, a physiotherapist along with a physician is needed to monitor and treat them. Psychological tests results also did not suitably fully fit with the ADHD diagnosis. It was felt following evaluating the boys that stimulant medication might benefit them. Administration of methylphenidate led to improved motor and cognitive functions as well as social adaptation of these boys. Treatment with methylphenidate thus might be considered in 47, XYY syndrome patients with similar clinical presentation.
Men with XYY syndrome or Klinefelter syndrome have been found to have an increased overall risk of conviction (excluding traffic offenses). However, when compared after adjusting for socioeconomic parameters, this rise appeared statistically insignificant. The conviction rate of 47, XYY males for sexual abuse, burglary, arson, and 'others' were found significantly increased. An association between the poor socioeconomic condition and the chromosomal aberrations can explain partly or fully the increased risk of convictions of 47, XYY males.
The mortality rate of these affected males is also found significantly higher if compared to the age and gender-matched controls from the background population. Furthermore, the causes of death are scattered uniformly throughout the all informative chapters according to the ICD-10. The identifiable causes of death of 47, XYY individuals are in a significantly higher proportion due to cancer, neurological disorders, pulmonary diseases, and trauma are due to some unspecified diseases. It is felt that there are many undiscovered facts about this syndrome that need to be explored. Further scientific researches are needed to explore the facts behind the clinical problems inherent with this disease which are responsible for higher incidences of mortality.
Each cell of a normal person possesses 46 chromosomes. Two chromosomes among of them, termed as X and Y, and are designated as sex chromosomes as they possess the capacity to determine whether a person will ultimately develop a male or female phenotypic characteristics. A normal female thus typically has one pair of X chromosomes (46, XX) and a normal male has one X and one Y as sex chromosome (46, XY).
XYY syndrome occurs due to the addition of an extra copy of the Y chromosome to that of a male's normal chromosomal pattern. With this addition, each cell now contains total 47 chromosomes instead of 46. This rearrangement of chromosomal number relates to the development of few abnormal phenotypically and behavioral characteristics like tall stature, macrocephaly, or learning disabilities. But it is unclear how the presence of an extra Y chromosome is linked with the development of these above-mentioned characteristics.
Inheritance is least likely related as a cause to the majority of 47, XYY syndrome. Actually this is a development defect of the sperm cells during their formation. There are random chromosomal changes while formation and maturation of sperm cells which could result in any form of aberration. This may lead to an accidental production of sperm cells with an extra copy of Y chromosome. This error in cell division called nondisjunction. If any of these atypical sperms with an extra Y chromosome fertilizes the ovum and thus subsequently contributes to the genetic makeup of a child; the boy will carry an extra Y chromosome in his body’s entire cell and thus develop XYY syndrome.
Following the incidence of Klinefelter syndrome, XYY sex chromosome aberration appears to be the second most common sex chromosome anomaly   . Its incidence appears to be approximately 1 out of 1000 live male births  . These boys have an increased puberty growth spurt and usually appear taller than the other normal boys with the same matched genetic growth potential. On an average, usually they have been found to have a 10- to 15-point IQ reduction compared to the other family members. Boys with this genetic makeup are usually prone to develop few physical disabilities along with minor behavioral disorders. Hyperactivity, attention-deficit disorder, and learning disorders are more commonly found in them in contrast to the general population.
An average prevalence of 14.1 per 100,000 of 47, XYY persons have been identified by a first nationwide study conducted to find its prevalence. However, this incidence appeared much lower than the expected incidence of 98 per 100 000 population. The average age of diagnosis of this syndrome is relatively late with a median of 17.1 years.
A 47, XYY karyotype is produced as a result of parental non-disjunction at the step of meiosis II and subsequent addition of an extra Y chromosome in the affected offspring   . In another way, 46, XY/47, XYY mosaics from parental nondisjunction during cell division after postzygotic mitosis can also result an addition of an extra Y chromosome in early embryonic development .
Studies have shown an increased association between 47, XYY and sub-fertility. Men with XYY syndrome can have variable sperm counts, ranging from normal to azoospermia          . Routine examination of the semen of men with XXY syndrome show increased incidences of spermatozoa with chromosomally anomaly         . Due to the greater prevalence of hyperhaploid sperm in their semen; there is also an increased risk of passing this extra Y chromosome to the offspring of 47, XYY male .
Considering the frequency of 47, XYY karyotype in the general population (one out of 1,000 newborn males), it is not often detected unless there is detection by prenatal testing. The clinicians must remain alert about the existence of this pathology and search for the new opportunities to find out appropriate educational interventions that target the specific learning challenges of XYY boys. Obviously, an early diagnosis carries a better prognosis of XYY and this message has to be forwarded to those involved in prenatal counseling and pediatric surveillance.
XYY syndrome, also referred to as 47, XYY syndrome, is a type of aneuploidy of the sex chromosome in males where they possess an additional Y chromosome. People with 47, XYY are clinically characterized by an increased growth velocity from childhood and a final tall stature. Macrocephaly along with few other typical facial features (mild hypertelorism, low set ears and a mildly flat malar region), delay in speech development are common to this disorder. They carry an increased risk for development of abnormal social and emotional bonding. In contrast to the general population, they are also found to have higher incidences of attention deficit hyperactive disorder and autistic spectrum disorder.
In XYY syndrome, the individual is phenotypically male, as instead of one, there is presence of 2 Y chromosomes, along with one X.
XYY syndrome is a disorder where a male is born with an extra Y chromosome. Frequency of this syndrome in the general population is about 1 in every 1,000 boys. Boys with this typical genotype tend to be taller and experiences difficulties in learning. They have a low intelligence quotient (IQ) when compared with the other family members. Learning disabilities, hyperactivity, attention deficit disorder, and minor behavioral disorders are more common among these boys. There was a previous speculation that XYY syndrome was related to aggressive or violent criminal behavior. But till today, no such proven data could be derived from the available scientific researches.