A chromosome is a package of DNA that exists inside the nucleus of a cell. A karyotype refers to the unique collection of chromosomes present in a person’s cells.

Acute myeloid leukemia (AML) is a type of blood cell cancer involving changes to the DNA of bone marrow. These changes can affect the combination of chromosomes that make up the karyotype.

AML karyotypes can be normal or abnormal, depending on whether their chromosomes have undergone changes. The karyotype is the main factor that doctors use to determine the disease prognosis for AML. This is because the type and number of chromosomal abnormalities present in the karyotype affect the severity of the disease.

This article outlines the difference between normal, abnormal, and complex AML karyotypes. We also provide information on how doctors diagnose AML karyotypes, and how this can affect a person’s treatment and prognosis.

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A metaphase is the point at which the genes in a cell turn into chromosomes. During the metaphase, chromosomes become visible under a microscope. Medical professionals use images of different cells during the metaphase to identify whether the cells contain abnormal karyotypes.

If cells have a normal karyotype, it means that the set of chromosomes within them appears normal.

For people with normal karyotype acute myeloid leukemia (AML), the overall prognosis is often more favorable. However, the immediate risk can still be high, particularly if treatment is not available.

Karyotype abnormalities occur when there is a mutation in the set of chromosomes within a person’s cells. The different types of chromosomal abnormalities that can cause abnormal AML karyotypes include:

  • Insertion: One chromosome contains contents from a different chromosome.
  • Deletion: A chromosome is missing some of its content.
  • Duplication: An area of a chromosome is multiplied.
  • Translocation: Multiple chromosomes share their content.
  • Inversion: An area within a chromosome is backwards.

The type of chromosomal abnormality within a set of chromosomes can sometimes influence the severity of AML. Some types of abnormality can have a favorable effect on a person’s prognosis while others can have a negative effect.

Favorable abnormalities include:

  • translocation between chromosomes 8 and 21
  • translocation between chromosomes 15 and 17
  • translocation or inversion of chromosome 16

Unfavorable abnormalities include:

  • translocation between chromosomes 6 and 9
  • translocation between chromosomes 9 and 22
  • translocation or inversion of chromosome 3
  • deletion of part of chromosome 5 or 7

A complex karyotype occurs when there are three or more chromosomal abnormalities occurring at the same time within a person’s sequence of chromosomes.

Complex karyotype AML typically has the most unfavorable prognosis, with every additional abnormality causing an increase in risk.

In order to assess a person’s karyotype, doctors will take samples of the person’s blood or bone marrow. The International System for Human Cytogenetic Nomenclature (ISHCN) lists criteria that doctors can use to distinguish between the different chromosomal abnormalities.

Using the ISHCN criteria, doctors are able to work out:

  • whether the karyotype contains abnormalities
  • which abnormalities the karyotype contains
  • how many abnormalities are present

A doctor will use that information to assess the impact the karyotype is likely to have on the course of the disease.

The prognosis for AML is generally most favorable when a person has normal karyotypes. For every unfavorable abnormality within a set of chromosomes, the prognosis for AML worsens.

An older study from 2010 suggests that having four abnormalities should be the differentiating point for the poorest prognosis. However, a 2021 review article suggests that having just three abnormalities is associated with the poorest prognosis.

One important reason for identifying AML karyotypes is that doctors use the results to work out appropriate treatment plans. A doctor will focus treatment on getting rid of any cells that contain abnormal karyotypes. The type of treatment the doctor recommends will depend on the type and number of chromosomal abnormalities.

For example, if test results show that the karyotype abnormalities are specifically from chromosomes that have translocated, a doctor may prescribe all-trans retinoic acid or “tretinoin” medication.

Stem cell transplantation may be a viable treatment strategy for some people who have multiple karyotype abnormalities.

A karyotype is the unique combination of chromosomes that a person has within each set of their DNA. A normal karyotype will not contain any chromosomal abnormalities, while an abnormal karyotype may contain one or more chromosomal abnormalities. A complex karyotype is a set of chromosomes containing three or more abnormalities.

The onset of acute myeloid leukemia (AML) is typically sudden. The disease severity and prognosis mostly depend on whether the AML karyotype is abnormal, and to what extent.

Understanding the AML karyotype is important for identifying an appropriate treatment plan. The type of treatment the doctor recommends will depend on the type and number of chromosomal abnormalities present within the karyotype. A person should talk to their doctor for more information regarding their AML karyotype and treatment plan.