What is Jacobs Syndrome?

Jacobs syndrome is a genetic disorder that results in male children possessing an extra Y chromosome. Not to be confused with the XXY chromosome that causes sterility in males, this condition does not usually result in any major physical abnormalities. Also known simply as 47,XYY, males with Jacobs syndrome do, however, grow to be taller than most males without this condition.

Normal people have a total of 46 chromosomes per cell. Out of these 46 chromosomes, two are the X and Y chromosomes, which determine whether a person will be born female or male. Those who receive two X chromosomes are born female, while those born with an X and a Y chromosome are born male. Individuals with Jacobs syndrome, however, have a 47th chromosome, which is an extra copy of the Y chromosome.

There is no known cause for Jacobs syndrome. Research indicates that this anomaly happens randomly and does not appear to be an inherited trait. While there also do not appear to be any major physical abnormalities in males with this syndrome, there do appear to be other differences between boys with this condition and those who are not born with an additional Y chromosome. Primarily, these differences include learning disabilities, delayed motor skill development, speech delays, behavioral problems and hand tremors.

At birth, parents and caretakers do not realize any abnormal symptoms associated with Jacobs syndrome. Boys with this condition do show signs of slower than normal rates of emotional maturity, as well as being slightly more physically active than others. By preschool age, some minor learning delays as well as speech delays may be noted, but these do not usually present a major interference in a boy’s learning or overall maturation.

Physically, boys with this condition appear to mature at the same rate as other boys in their age group. The only remarkable difference is that boys with an extra Y chromosome tend to grow taller than average, but not abnormally so. Males with this syndrome progress to puberty at the same rate as other boys, are fertile and do not present any hormonal differences from others boys and young men their age.

Mentally and emotionally, boys with Jacobs syndrome do show a very slight risk of developing mental and social issues, but only if they are not reared in loving and supportive environments. Research shows that males with an extra Y chromosome who are reared in poor environments where stimulation and love are lacking show a slightly increased risk of developing maladaptive behaviors than other siblings in the same home. At one point in history, this condition was widely associated with criminal behavior, but contemporary research has proven that this simply is not true.