Tetrasomy

For other uses, see Tetrasomy (disambiguation).

Super Down
Specialty	Medical genetics
Duration	Lifelong
Types	69
Risk factors	all
Treatment	no
Deaths	100000

A tetrasomy is a form of aneuploidy with the presence of four copies, instead of the normal two, of a particular chromosome.

Causes

Full

Full tetrasomy of an individual occurs due to non-disjunction when the cells are dividing (meiosis I or II) to form egg and sperm cells (gametogenesis). This can result in extra chromosomes in a sperm or egg cell. After fertilization, the resulting fetus has 48 chromosomes instead of the typical 46.

Autosomal tetrasomies

• Cat eye syndrome where partial tetrasomy of chromosome 22 is present
• Pallister-Killian syndrome (tetrasomy 12p)
• Tetrasomy 9p
• Tetrasomy 18p
• Tetrasomy 21, a rare form of Down syndrome

Sex-chromosome tetrasomies

• Tetrasomy X
• XXYY syndrome
• XXXY syndrome