Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
Tetrasomy
Introduction
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 tetrasomy of chromosome 22 is present
- Pallister-Killian syndrome (tetrasomy 12p)
- Tetrasomy 9p
- Tetrasomy 18p
Sex-chromosome tetrasomies
- 48, XXXX syndrome
- 48, XXYY syndrome
- Klinefelter’s syndrome, where XXXY tetrasomy is present