Story 05 · Genes and medicine
One letter of DNA that changes the shape of a blood cell
Sickle cell disease comes from a single change in one gene, it was the first illness traced to a specific molecule, and the same change that harms people with two copies protects carriers from severe malaria.
- Sickle cell disease
- Worldwide
- 1949
- 3 min read
On this page
Before you readWhat would you do?
Two people planning to have children both learn they carry sickle cell trait. A chatbot tells them "carriers are healthy, so there is nothing to worry about". What is the most accurate next step?
Pick an answer now. The file tells you whether you were right.
01The file in one minute
1One change
A single change in the HBB gene alters haemoglobin, so red blood cells can bend into a sickle shape.
2A molecular disease
In 1949 Linus Pauling's team traced the illness to a change in one molecule, among the first ever.
3Carriers
One copy usually causes no serious illness and protects against severe malaria. Two carriers have a 1 in 4 chance per pregnancy.
4The lesson for AI
Whether a pattern helps or harms depends on context. Check a tool was tested in conditions like yours.
02Timeline
1910
A US doctor describes sickle-shaped red blood cells in a patient.
1949
Pauling and colleagues call sickle cell anaemia a "molecular disease".
1950s
Researchers link sickle cell trait to protection against malaria.
2023
The first gene-editing therapy for sickle cell disease is approved.
03The story
Red blood cells carry oxygen using a protein called haemoglobin. In sickle cell disease, a single change in the HBB gene alters one building block of that protein. When oxygen is low, the changed haemoglobin can clump, bending red blood cells into a stiff crescent or sickle shape. These cells can block small blood vessels, causing severe pain, infections, anaemia and organ damage.
In 1949 Linus Pauling and colleagues showed that haemoglobin from people with the disease behaved differently in an electric field, and called sickle cell anaemia a "molecular disease". It was one of the first times an illness was traced to a change in a specific molecule.
The condition is recessive. A person with one changed copy, called sickle cell trait, usually has no serious illness. Two carriers have a 1 in 4 chance in each pregnancy of a child with the disease. Carriers have some protection against severe malaria, which helps explain why the trait is common in parts of Africa, the Middle East and India. Treatments include medicines such as hydroxyurea, blood transfusions, bone marrow transplants, and since 2023, gene-editing therapies in some countries.
04What the science says
The same gene change can help or harm depending on how many copies a person has and where they live. In places with malaria, carrying one copy gave a survival advantage, so the gene stayed common over many generations.
The AI angle: whether a pattern helps or harms often depends on context. An AI rule that works in one setting can fail in another, so check that a tool was tested in conditions like yours.
The idea behind this caseLesson: How machines learn →
05What to take from it
- Remember that a gene is not simply good or bad. Effects depend on copies, environment and other genes.
- If sickle cell disease runs in your family, carrier testing before pregnancy can help you plan.
- People with sickle cell disease need regular care from a specialist team. Sudden pain, fever or breathing problems need urgent medical help.
- Talk to a doctor or genetic counsellor about testing and what results mean for your family.
07 — Sources
- Sickle Cell Anemia, a Molecular Disease · Science · 1949-11-25
- Sickle cell disease · MedlinePlus Genetics, US National Library of Medicine · 2024
- Sickle cell disease · NHS · 2024