Klinefelter’s syndrome is named after Harry F. Klinefelter (cline-felter) who first described the syndrome in the USA in 1942.
It is a genetic disorder that only affects male. Normally a person, whether male or female, has a total of 46 chromosomes in the nucleus, which is the control centre of each cell. Chromosomes are the genetic material that contain the code of life: Deoxyribonucleic acid, better known as DNA. Of those 46 chromosomes, 44 are grouped in a total of 22 pairs and are called autosomes, the name given to the non-sex determining chromosomes that determine other characteristics. In addition there are normally two sex chromosomes, females having two X chromosomes and males having one X and one Y. Each chromosome is made up of genes, each of which has a specific role to perform. The Y chromosome contains the male determining gene. Of the 46 chromosomes, half come from the mother and half from the father.
A normal male would have 44 autosomes and the X and Y sex chromosomes, making a total of 46. This is expressed as 46,XY and is known as that individual’s karyotype (carry-o-type). In Klinefelter’s syndrome however, due to one of nature’s accidents, when the male sperm fuses with the female egg, the fetal cells have at least one extra X chromosome. The most common number of chromosomes found in KS is 47, that is 44 autosomes and 3 sex chromosomes giving a karyotype of 47,XXY.The extra X chromosome can come from either a sperm or an egg, with a 50:50 chance.
However as maternal age increases so does the risk of having a boy with KS. The same risk does not however occur as men get older. Because KS is not passed on but occurs by accident, it is said to be congenital, which means that it is not inherited, that is, it is not an hereditary disorder. This means that the parents of a boy who has Klinefelter’s syndrome need not be anxious about having more children as the likelihood of having another KS boy is minimal.
What is a Mosaic/Mosaicism?
Some KS males have what is known as mosaicism (mose-aia-sisem) which means that some of the cells in their body are ordinary 46,XY whilst others are, for example, 47,XXY. This example would be expressed as 46,XY/47,XXY. Some of these individuals, because of where the normal 46,XY cells are located, are able to produce sperm and father children, whereas the majority who are non-mosaic are sterile, that is, they are unable to produce sperm and father children.