The U.S. National Library of Medicine's Genetics Home Reference website says Triple X Syndrome, also known as Trisomy X or Trisomy 47, is a genetic condition where females have three X chromosomes instead of two. The European Journal of Human Genetics reports it affects one in every 1,000 females. Physical symptoms are mild and females with Triple X may be taller than average, have a smaller head, experience problems with motor, speech and language development and have behavioral, emotional and learning problems.
Basic Genetics
Each cell has 46 chromosomes, tiny structures that contain genetic information, existing in 23 pairs. One pair, the sex chromosomes, determine whether a person will become male or female. A female has two X chromosomes, inheriting one from each parent, says the Mayo Clinic. In Triple X syndrome, a girl inherits an extra X chromosome.
Nondisjunction
Some time during the production of a sperm cell or egg cell, an error in cell division occurs, a random act called nondisjunction. In this case, the child develops from a sperm or egg cell with an extra X chromosome, resulting in every cell of her body having an extra X chromosome, and the characteristics associated with Triple X syndrome.
Chromosomal Mosaicism
Chromosomal mosaicism is also due to a random error in cell division. The difference in this case is the egg and sperm are normal at the time of fertilization. The error occurs after fertilization, but early in embryonic development. This means that some of the girl's cells will have two X chromosomes, while others will have three. The characteristics due to this error will vary depending on the number of affected cells.
Hereditary
Triple X Syndrome is a genetic disorder, meaning it is due to an abnormality in chromosomes, but is not usually inherited, or passed down from a mother or father, and is instead the result of a random error in cell division. However, according to the European Journal of Human Genetics, researchers have found an association between increased maternal age and occurrence of Triple X Syndrome.
