Eye care in the community 6: Klinefelter syndrome

Normally we all possess 46 chromosomes made up of 22 pairs of autosomes and one pair of sex chromosomes. Klinefelter syndrome is a chromosomal condition affecting boys and men. It is not inherited, but instead is due to an error during cell division called non-disjunction. This prevents the X-chromosome being distributed between the gametes, the egg and sperm cells. In essence, the egg cell that normally has an X-chromosome will have an extra X-chromosome or the sperm cell that normally has a Y chromosome may end up with another X-chromosome
(figure 1).

Therefore, if an egg with XX chromosome is fertilised by sperm with a Y chromosome, then we will get XXY child. Likewise, when a sperm with an X and Y chromosome fertilises an egg with a single X chromosome, the child will also have XXY chromosomes. In both cases, Klinefelter syndrome results. So Klinefelter’s is not due to gene mutation and inheritance but instead is due to their now being 47 chromosomes instead of 46.