Last updated: November 9, 2023

What Does Aneuploidy Mean?

Aneuploidy is a state of having an abnormal number of tightly coiled DNA molecules, called chromosomes, rather than the normal 23 pairs or 46 chromosomes. The abnormal number can be greater or smaller than the normal number of chromosomes. Aneuploidy results in various genetic disorders that have been present since birth. Examples of such disorders include Down syndrome, Turner’s syndrome, and sex chromosome disorders. An aneuploid cell is formed during the period when the cell is dividing and its chromosomes haven’t yet parted completely.

FertilitySmarts Explains Aneuploidy

Types of aneuploidy

Normally, a chromosome is arranged in a pair of two. When there are three copies (one extra copy or 47 chromosomes instead of 46), it is called as trisomy. Alternatively, an aneuploid cell may be missing one chromosome from a pair – termed as monosomy. Very rarely, a chromosome can have four or five copies, known as tetraploidy. The most common aneuploidy is Down syndrome (or trisomy 21 with an extra copy of chromosome 21).

What causes aneuploidy?

Normally, during cell division, the cells destined to produce sperm and eggs divide equally so that both the sperm and eggs have the same number of chromosomes. However, an uneven division of chromosomes during cell division can end up in a sperm or egg having an unequal number of chromosomes.

Outcomes of aneuploidy

The aneuploidy that stems from errors in chromosomal separation is the leading cause of miscarriages, infertility, and inherited birth defects. A majority of the aneuploid fetuses fail to survive to term and are spontaneously miscarried half way. It is also one of the most common causes of in vitro fertilization (IVF) failure.

How is aneuploidy diagnosed?

It is diagnosed through a chromosomal study, called karyotyping – a study that evaluates the size, shape, and number of chromosomes in a sample of cells. It can be done on the amniotic fluid and placenta.

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