How can a single mutation in the gene for a protein such as hemoglobin affect several body systems?

Hemoglobin is made of three components: hemo, alpha (or alpha-like) globin, and beta (or beta-like) globin.

 Changes in globin production (more or less than normal) can cause mutations in alpha or beta globin gene, these changes leading to one type of thalassemia, which is a quantitative hemoglobin disease.

Another blood disorder, caused by a mutation in the HBB gene is sickle cell anemia, where the cells have the C-shape. Cells' flexibility is reduced by the process of sickling and the risk of developing complications is growing. This kind of blood disorder could be found in regions where malaria occurs. In C-shape cells malaria parasite could be destroyed before emerging the daughter parasite.