Book Review

Smell and Taste in Health and Disease

N Engl J Med 1993; 328:143January 14, 1993

Article

Smell and Taste in Health and Disease
Edited by Thomas V. Getchell, Richard L. Doty, Linda M. Bartoshuk, and James B. Snow, Jr. 883 pp., illustrated. New York, Raven Press, 1991. $165. ISBN: 0-88167-798-1

“Nobody ever died because he couldn't smell.” So said a grants administrator at the National Institutes of Health in trying to explain why so few research dollars address smell and taste. As compared with vision and hearing, these “chemical senses” have been neglected. The situation is changing rapidly, as molecular research is making major strides in elucidating the mechanisms of olfactory and gustatory signal transduction. Moreover, clinical ramifications of substantial importance are becoming evident for research on both of these senses.

This is a landmark book that comprehensively and thoroughly explores all the important aspects of smell and taste, ranging from anatomy, physiology, and biochemistry through clinical aberrations of taste and smell and their treatment. The authors include leading authorities in the field, both basic scientists and clinicians, especially otolaryngologists. The notion that abnormalities in smell and taste cause little distress is belied by Tennen, Affleck, and Mendola's quotations from patients with loss of smell: “I have no ability to defend myself . . . against natural gas, fire related problems”; “I began to feel different from everybody else, thus creating feelings of isolation and ultimately rage”; “I wonder if my sex drive is down because I can't smell him”; “Life in general is not as good. A great pleasure is gone from my life.”

The chemical senses are notable for the way in which clinical and basic research interdigitate. For instance, one of the biggest riddles in olfaction is the number of distinct odorant receptors. Most humans can smell five thousand or more odorants, but high-school algebra tells us that differential effects of odorants on a dozen or fewer separate receptors could account for this variety. Until recently, insights into this olfactory “code” had come largely from psychophysical studies characterizing specific anosmias in the human population. Surprisingly large numbers of people cannot detect one odorant or another, with many of these anosmias regulated genetically. In part on the basis of data on anosmia, scientists for years have formulated groups of primary odors, presumably reflecting distinct receptors. The first effective categorization, which has influenced classification systems to the present, was conceived by Linnaeus in 1756 and is reviewed in a chapter by Doty. Amoore's chapter describes his classic studies classifying distinct anosmias and suggesting the existence of seven primary odors. Subsequent work increased his list to an absolute minimum of 36, with the possibility of more than 100 primary classes. These newer data mesh beautifully with the recent molecular-biologic advance by Linda Buck and Richard Axel, who sought odorant-receptor genes, on the premise that they are part of the class of G protein-linked seven-transmembrane-domain receptors. They uncovered a large family of distinct odorant-receptor genes numbering at least several hundred. Their work is profoundly influencing thinking in the field but is too recent to have been included in this book.

A chapter by Kinnamon and Getchell reviews the basic mechanisms of transduction in receptor cells for both smell and taste. For most odorants, olfactory transduction involves the conventional second messengers, cyclic AMP and the phosphoinositide cycle. Greater diversity is evident for taste. Sweet taste largely involves cyclic AMP, whereas bitter taste employs the phosphoinositide system. Sour and salty tastes use novel systems. Sour taste derives from protons that interact directly with a unique potassium channel located at the tip of the taste buds. Schiffman's chapter describes her work showing that humans and animals treated with the diuretic drug amiloride are less able to detect salt. Amiloride acts as a diuretic by binding to specific receptors in the kidney associated with a unique type of sodium channel. By inference, a related type of amiloride-receptor sodium channel in the tongue presumably mediates the perception of salty taste.

Several chapters deal with smell and taste disorders in disease states. Doty describes striking alterations in patients with neurodegenerative diseases. Patients with Parkinson's and Alzheimer's diseases have decreased smell perception. In Alzheimer's disease the pathologic plaques and neurofibrillary tangles are most pronounced in parts of the brain linked to the olfactory system. These findings suggest that a virus or toxin entering the brain through the nose participates in the pathogenesis of the disease. The wide range of the areas covered as well as the solidly written, authoritative chapters makes this book indispensable for researchers and clinicians interested in the chemical senses.

Solomon H. Snyder, M.D.
Johns Hopkins University School of Medicine, Baltimore, MD 21205