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Diagnosis and tests

DNA and mutations

The related article (“Molecular tests: PCR and NGS”) explains part of the blood count. This topic explains what DNA is, how a mutation arises and how mutations are named in leukaemia reports.

Last updated: ~2 min read
DNA with one rung in a different colour.
Figure 1.One rung of DNA has changed.

01Short answer

DNA is the cell’s “instruction book”: a long chain of four “letters”, with genes as the chapters. Each time a cell divides, its DNA is copied, and sometimes a mistake happens; this is a mutation (a variant). Most mutations are harmless, but some give a cell an “advantage”: dividing faster or not dying. That cell multiplies and forms a clone. In leukaemia there are usually several mutations together: “driver” mutations push the disease on, while “passenger” mutations happen by chance. These mutations are acquired during life (somatic): they are present only in blood cells and are not passed to children. Rarely there is an inherited tendency (germline), which needs special assessment.

02Simple explanation

DNA: the cell’s instruction book.

A mutation: a copying mistake.

Usually acquired, not inherited.

03Scientific explanation

Variant allele fraction (VAF): a percentage in the report showing what share of the sample carries the mutation; a very high VAF sometimes raises the possibility of an inherited variant.

Naming: for example NPM1 c.860_863dup gives the gene name and where in the DNA the change is; your doctor explains what it means.

04What happens in the body?

One rung changed

A change in one rung of the DNA ladder can be a mutation.

Acquired, not inherited

Leukaemia mutations usually start in one cell and are not passed to the family.

A family silhouette and one cell.
Figure 2.An acquired change in one cell.

Driver and passenger

Some mutations drive the disease; others are just along for the ride.

Two cars of light on a DNA road.
Figure 3.Driver and passenger mutations.

05From mutation to clone

Four steps.

DNA — A normal strand.1DNAA normal strand.
Mistake — A change when copying.2MistakeA change when copying.
Advantage — The cell grows faster.3AdvantageThe cell grows faster.
Clone — Identical cells multiply.4CloneIdentical cells multiply.

06Types of mutation

TypeSimple explanation
PointOne letter changed
Insertion / duplicationLetters added (for example NPM1)
DeletionLetters lost
ITDA section repeated (for example FLT3-ITD)
FusionTwo genes joined (for example BCR::ABL1)

07Key terms

DNA
The molecule that carries genetic information.
Gene
A section of DNA with instructions for a protein.
Mutation / variant
A change in DNA.
Somatic
Acquired during life, not inherited.
VAF
Variant allele fraction.

08Key points

  • DNA is the cell’s instructions.
  • A mutation is a copying mistake.
  • Some give the cell an advantage.
  • Leukaemia usually has several mutations.
  • Most are not inherited.
  • Let your doctor explain the report.

09Frequently asked questions

What caused the mutation?

Often it is unknown; random mistakes build up with age, and sometimes radiation or certain chemicals play a part.

Should my children be tested?

Usually not; if an inherited cause is suspected, your doctor will refer you.

My VAF went down; is that good?

It often reflects response to treatment; your doctor will tell you what it means.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. What caused the mutation?

  2. Should my children be tested?

  3. My VAF went down; is that good?

My questions

12Sources

  1. MedlinePlus Genetics. What is a gene variant and how do variants occur?
  2. National Cancer Institute (NCI). Adult AML treatment (PDQ), patient version
  3. National Cancer Institute (NCI). Tumor markers in common use
  4. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: bone marrow biopsy
  5. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: karyotype
  6. National Cancer Institute. NCI Dictionary of Cancer Terms: complete blood count
  7. MedlinePlus (U.S. National Library of Medicine). Hemoglobin Test
  8. MedlinePlus (U.S. National Library of Medicine). Platelet Tests
  9. Blood (American Society of Hematology), 2019. Management of acute promyelocytic leukemia: updated recommendations from an expert panel of the European LeukemiaNet
  10. MedlinePlus (U.S. National Library of Medicine). Bone Marrow Tests
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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