Their Mutated Genes Were Supposed to Be Harmless

"Sid was in medical school at the time, and he immediately thought of a few genetic conditions that could explain this result. One was thalassemia, which causes low levels of hemoglobin, leading to anemia and other related problems. A laboratory test showed that he had this inherited illness. And this meant that he had a gene mutation. Finally, he thought, he had an explanation for symptoms he had been experiencing for years."

"In the most common forms of thalassemia, people who show symptoms have mutations in both copies of the related genes. Those born with the most severe forms of thalassemia require transfusions for life to get enough healthy red blood cells, and if the condition is not diagnosed soon enough it can be fatal in early childhood. But Sid's lab results suggested that only one copy was affected, so he was considered a carrier of the illness,"

Carriers of thalassemia can experience measurable health consequences such as lethargy and fainting despite having only one mutated gene copy. Common tests can show anemia and smaller-than-normal red blood cells in carriers. Most severe thalassemia arises when both gene copies are mutated, often requiring lifelong transfusions and risking fatal outcomes in early childhood if not diagnosed. Carriers historically were considered asymptomatic and mainly important for reproductive risk, but carrier-status symptoms can still impair daily life. Many other inherited conditions may likewise cause unrecognized health effects in carriers, expanding the clinical relevance of single-copy mutations.

Read at The Atlantic