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Genetic and Rare Diseases Information Center (GARD)

Other Names for this Disease
  • 48 XXXX
  • 48 XXXX syndrome
  • Tetra X
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What causes tetrasomy X?

Tetrasomy X is usually caused by a random error in the formation of an egg cell (before pregnancy). In some cases, it may be due to inheriting three X chromosomes from the mother and one X chromosome from the father. In other cases, it may be due to inheriting all four X chromosomes from the mother. During the normal formation of egg cells, each egg cell contains one X chromosome to pass on to offspring. However, errors in cell division can cause an egg cell to have three or four X chromosomes, instead of one. If an egg cell with the extra X chromosomes is fertilized by a sperm cell with one X chromosome, the resulting embryo will have these extra chromosomes. Rarely, tetrasomy X may be caused by an error in cell division that occurs after an egg is fertilized, or by the presence of extra X chromosomes in some of the mother's cells.[1]
Last updated: 2/19/2014

  1. Tetrasomy X. Unique. 2005; Accessed 2/19/2014.