Aneuploidy is a condition in which there is a mutation in the number of chromosomes. The chromosomes are those having structures body formed by DNA and proteins. These are essential for a good development since they contain all the genetic information of a person.


Medical genetics

  • ICD-10: Q90-Q99
  • ICD-9: 758
  • MeSH: D000782

What is Aneuploidy?

It is a chromosomal alteration in the number of chromosomes caused by a genetic mutation. There may be an excess or a decrease in the number of chromosomes. Aneuploidy is responsible for the majority of genetic mutations or syndromes present in fetuses and newborns. It can even cause spontaneous abortions during the gestation period.


In aneuploidy, there is a notable change that originates in the cell, causing more or fewer chromosomes to exist than normal, causing different types of genetic mutations or syndromes in the fetus. It is also possible to find this type of change in the cell in cancerous processes. The best known aneuploidy around the world is Trisomy 21 . When the number of chromosomes is abnormally greater it will cause spontaneous abortions during gestation. If the number of chromosomes is less it is known as monosomyand it is responsible for triggering Turner Syndrome. Generally, these patients have deficiencies in their physical or mental development or both. On many occasions, there are interruptions in pregnancy, this being a very common complication of the condition. All the changes that occur in the genetic material are known as mutations.

  • Causes of aneuploidy
  • Types of aneuploidy
  • Risk
  • Treatment of aneuploidy
  • Aneuploidy in pregnancy

Causes of aneuploidy

The chromosomal changes that lead to aneuploidy can be caused by two reasons. The first, because there is a notable delay in the meiosis of the chromosome causing it to be lost during anaphase (stage in which the chromosomes separate). The second and most common cause is because an adequate disjunction or meiotic segregation does not occur during meiosis or mitosis . When we refer to disjunction, we speak of the normal segregation of the body’s chromosomes, nondisjunction indicates that there has been a problem in the chromosome formation process.

Types of aneuploidy

Every human being has a set of 46 chromosomes arranged in two sets or pairs of chromosomes. When this happens it is said to be a euploid cell and indicates that the chromosome sets are correctly organized into complete and organized sets. On the contrary, when there are more or fewer chromosomes than the normal number, we say that it is an aneuploid cell.

Aneuploidies are classified in two ways:

  • Depending on the type of chromosome that is affected: sexual or autosomal. Aneuploidy of the sex chromosomes and autosomal aneuploidy.
  • According to the number of chromosomes that are in excess or that are missing:
    • Nulisomy –  A pair of homologous chromosomes is missing.
    • Monosomy:   occurs when a single non-sexual chromosome is missing.
    • Disomy: when it has two extra chromosomes.
    • Trisomy: it is when there is a single extra chromosome, this means, it will have 47 chromosomes in total.
    • Tetrasomy: refers to the gain of two chromosomes, the individual will present 48 chromosomes.
    • Pentasomy: is the presence of three x chromosomes in women.


The main risk factor that exists for the presence of aneuploidy is maternal age , although this relationship is unknown for sure, however, studies indicate that advanced age, mainly more than 45 years, is closely related to the appearance of the anomaly, mainly due to the increase or decrease in the number of chromosomes in the cell since the ovules are older and are more likely to lose disjunction. The main risk for the fetus is developing a genetic diseasethat puts your life at risk or causes early termination of pregnancy. Embryos that do not have some of their sex chromosomes do not manage to complete their development until birth, so this type of monosomies are lethal. Trisomies also prevent the full development of the embryo, however, in some cases, an extra copy of the chromosomes allows them to survive for several years with serious problems in their physical development.

Treatment of aneuploidy

There is no indicated treatment for the genetic mutation. Mainly, it is based on giving support measures to patients suffering from the disease to provide them with a better quality of life.

Aneuploidy in pregnancy

Prenatal detection of aneuploidy has changed in recent years because now, thanks to technology, they can be accurately identified. Detection of DNA in the fetus in maternal blood can detect some of the most common trisomies of the sex chromosome. These procedures are most successful in women over 45 years of age. Education and psychological support are an important part of treatment once chromosome errors are diagnosed.

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