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Xyy Syndrome, Jacob Syndrome

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XYY Syndrome, Jacob Syndrome

XYY Syndrome, better known as the Jacob Syndrome is a rare genetic disorder which affects males due to an extra Y chromosome. Healthy males have 46 chromosomes including one X and one Y chromosome. Men with XYY syndrome have 47 chromosomes, two of which are Y chromosomes. It is not known why the extra Y chromosome occurs. The disorder is present at birth and is estimated to occur in one out of every one thousand live births (1). In very rare instances, the syndrome has been passed from father to son, but in most cases heredity cannot be established.

XYY syndrome is a chromosomal condition which occurs only in males and is found with a frequency of 1 in 1,000. A chromosome is a rod-like structure present in the nucleus of all body cells, with the exception of the red blood cells. Chromosomes store genetic information. Normally humans have 23 pairs of chromosomes, 46 chromosomes in total. The 23rd pair, otherwise referred to as the sex chromosomes, store genetic information which determine our sex(2). A female has a XX pair and a male has a XY pair of chromosomes.

A male affected by XYY syndrome has an additional Y chromosome as well as the usual XY pair of chromosomes resulting in the formation of XYY. Sometimes the additional Y chromosome is present in only some of the cells of the body, but not all. This is referred to as a mosaic form of XYY syndrome. The extent to which such an individual is affected by XYY syndrome depends upon the proportion of XYY cells to XY cells throughout the body(4).

The effect of having an extra Y chromosome in some or all cells varies between individuals. Some males with XYY syndrome show very few symptoms. The majority are never diagnosed whilst others may be more severely affected. Additionally, individuals may be differently affected by the severity of their features. It is not possible, therefore, to offer a precise prediction of the symptoms before or even immediately after the birth of each XYY boy(5).

You cannot see on a newborn boy, that he has the XYY syndrome. Except for increased height there are nospecial physical stigmata in boys and men with XYY syndrome. Their average height is approximately 7 cms. above the expectedheight. Physical development

is otherwise normal, sex-organs are normal.

Boys with XYY syndrome often are more physically active than their brothers, and if this activity is canalized into play,sports or other physical activities with parent and other children, this fact is in no way negative. Boys with XYY syndromehave a tendency to a delayed mental maturation, and in connection with an increased tendency for learning-problems inschool, this means a need for early and adequate stimulation(3). XYY boys grow taller than average, they have a 'growth spurt' during childhood which results in an average height of 6'2". In early childhood, XYY boys are very active, with good eating and sleeping patterns. During adolescence they may experience severe acne.

In some cases, XYY males show learning difficulties, with slightly lowered intelligence scores for the group compared with XY males. They may have delayed speech development and have difficulties in communication. Boys with an extra Y chromosome seem to be at higher risk of having problems at school. However, regular assessment of educational achievement allows early intervention and helps to prevent secondary behavioural problems(1). Some XYY boys have obtained degrees at University.

Behavioural problems involve difficult and defiant behaviour which usually starts in childhood. Temper tantrums are common. It has been suggested that XYY males are predisposed to commit criminal acts more frequently than expected. Long-term follow-up studies are currently underway to shed more light on this issue and, to date, show that the frequency of conviction does not differ from that found in XY boys of the same level of intelligence(5).

The characteristics of XYY syndrome are often very subtle and do not indicate and serious chromosomal disorder. Therefore, males with this condition are frequently undiagnosed or misdiagnosed. The primary symptoms include tall or very tall height which becomes evident at the age of five or six, and severe cystic acne during adolescence.

Lower than average intelligence and/or behavioral problems, such as an explosive temper, aggressive or defiant actions, or sometimes antisocial behavior are

other symptoms(2). Some individuals with this disorder may also have language

difficulties or psychosexual problems. XYY Syndrome is often undiagnosed until

tests for other medical reasons are performed. Other than being unusually

tall and/or having behavioral problems, in many cases, these boys or men appear


XYY syndrome typically causes no unusual physical features or medical problems. Persons with this syndrome may be slightly taller than average, or have more severe acne than



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