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...
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