Sickle cell anemia as a molecular disease

The disease had been on record since 1910, when Ernest Irons, an intern at Presbyterian Hospital in Chicago, noticed elongated red cells in a blood smear from a dental student with severe anemia, and James Herrick published the case.

Linus Pauling, a chemist at Caltech, first heard of sickle cell anemia in 1945 from William Castle of Harvard Medical School. Both sat on a medical advisory committee preparing part of Vannevar Bush's report Science, the Endless Frontier. Castle mentioned that the patients' red cells looked normal in arterial blood and turned crescent-shaped in venous blood. Because only cells that had lost their oxygen sickled, Pauling reasoned that hemoglobin was involved, and that an abnormal hemoglobin might stick to itself when deoxygenated and bend the cell. Another committee member, Ed Doisy of St. Louis University, suggested that Pauling take Doisy's newly graduated medical student, Harvey Itano, as a chemistry doctoral student.

Pauling's group, with Itano, S. J. Singer and Ibert Wells, ran hemoglobin from patients and healthy adults through Caltech's Tiselius electrophoresis apparatus. Pauling and Itano announced the first results in March 1949 and the full paper in Science followed in November. At pH 7.0 the carbon monoxide form of sickle cell hemoglobin moved as a positive ion and the normal form as a negative one; the authors put the difference at two to four extra positive charges. The heme groups were identical, so the difference lay in the globin. Hemoglobin from healthy people of European and African descent could not be told apart. Blood from people with sickle cell trait held both kinds, roughly 60 percent normal to 40 percent sickle. The authors concluded that patients were homozygous and carriers heterozygous, the same conclusion James Neel of the University of Michigan had reached from family studies and published in Science four months earlier. The Caltech group stated that they had reached it on their own.

In 1956 Vernon Ingram, a protein chemist at the Cavendish Laboratory in Cambridge, compared the two hemoglobins by fingerprinting, spreading their peptides across paper by electrophoresis and chromatography. One spot differed. Less than a year later, in a 1957 paper in Nature, he showed that the change was a single amino acid, valine in place of glutamic acid, which explained the charge difference. The substitution sits at the sixth amino acid of the beta globin chain.