The Importance of the Concept of Molecular Disease

Flyer for "Abnormal Human Hemoglobin Molecules in Relation to Disease." November 6, 1956.

Flyer for "Abnormal Human Hemoglobin Molecules in Relation to Disease." November 6, 1956.

The idea of Dr. Linus Pauling that an abnormal hemoglobin molecule might be responsible for the sickling process initiated the study of the hemoglobin molecule in hereditary anemias.
- Harvey Itano. “Clinical States Associated with Alterations of the Hemoglobin Molecule.” Archives of Internal Medicine, 96: 287-97, 295. 1955.

During his lengthy career, Linus Pauling maintained a long-running interest in the relationships between chemistry and the human body. In the mid-1930′s, he began to work extensively with the hemoglobin molecule. As we’ve seen in previous posts, this research would eventually lead to many important discoveries and his coining of the term “molecular disease.”

Sickle cell anemia was the first disease to be classified as a molecular disease. As was mentioned in this post, Pauling first learned of the disease in the spring of 1945 when Dr. William B. Castle, a physician and Professor of Medicine at Harvard University, described it at a meeting of the Medical Research Association. As Dr. Castle listed off the characteristics of the disease, Pauling, through the prism of his deep knowledge of the structural chemistry of hemoglobin, developed an almost-immediate formulation of sickle cell anemia as a disease of the hemoglobin molecule, rather than of the entire blood cell.

Listen: William Castle recounts his first meetings with Linus Pauling…

Listen: …and Pauling responds in kind

A few months later, Pauling would pass this idea on to Harvey Itano, who was completing his doctorate in chemistry at Caltech. Itano conducted a series of initial experiments on the hemoglobin molecule, all of which failed. After months of tedious investigation, however, Itano, Dr. S. J. Singer and Dr. Ibert C. Wells – both of them newly-minted Ph.D.’s – were able to use the techniques of electrophoresis to identify a significant distinction. The paper “Sickle Cell Anemia, a Molecular Disease” was then published in the fall of 1949 and the concept of molecular disease was instantly established.

Listen: Pauling describes the Itano, Singer and Wells electrophoresis experiments

Although Pauling wasn’t the first to think about diseases in terms of molecular aberrations, no one prior to the Pauling-Itano group had concretely demonstrated their existence. After their initial success, Singer and Itano continued to expand on the original research, eventually discovering a less-severe case of sickle cell anemia called sicklemia. The duo also described the manner in which sickle cell anemia is inherited. As such, not only did Pauling and his colleagues identify the exact source of the disease, they also provided a link to genetics and confirmed Pauling’s view that analysis on a molecular level can provide valuable information. Later, Itano would discover more abnormal hemoglobin molecules, and the molecular analysis of diseases would continue.

Illustration from Medical World News article, "Sickle Cell Anemia" December 3, 1971.

Illustration from Medical World News article, "Sickle Cell Anemia" December 3, 1971.

Since Pauling’s coining of the term “molecular disease,” many other diseases have been similarly categorized: Hemophilia, Thalassemia, Alzheimer’s Disease and Muscular Dystrophy to name a few. (Though it could also be argued that every heritable disease can be classified as a molecular disease because these diseases require a modified genetic component that can be passed from parent to child.)

Thalassemia, for example, is also a disease of the hemoglobin molecule. However, while sickle cell anemia is caused by the production of abnormal hemoglobin, Thalassemia, conversely, involves the abnormal production of hemoglobin. More specifically, in cases of Thalassemia, the rate of production of a specific globin chain is decreased, which then causes the formation of abnormal hemoglobin molecules.

Pauling’s conceptualization of sickle cell anemia as a disease of the hemoglobin molecule jump-started years of research pertaining to abnormal hemoglobins and opened many new doors in the study of inherited diseases. Although he wasn’t directly involved in the discovery of the abnormal hemoglobin molecules, Pauling’s development of the concept of molecular disease was achievement enough to significantly raise his stature in the medical community (at least for a while) and further cement his status as a scientist of world-historical importance.

For more information on molecular disease and other related topics, please visit the website “It’s in the Blood! A Documentary History of Linus Pauling, Hemoglobin, and Sickle Cell Anemia.”

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One Response

  1. Very interesting article. informative and helpful in understanding the role of the hemoglobin molecule in disease. Thank you for publishing it.

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