As you may already know, we differ enormously from each other in the number of fungiform papillae that we have in the front of our tongues. Fungiform papillae are the little pink bumps on the front part of our tongues. These fungiform papillae house taste buds, with their taste pores that open up to the surface of the tongue. This picture (courtesy of Tim Hanni MW) shows the tip of a tongue with an abundance of fungiform taste papillae, that look like bubbles. The dark spots are the taste pores. The red circle surrounds a taste papilla.
Brillat-Savarin, the great French gastronome, in his "Physiologie du Gout" mentioned that the sensation of taste resided in these taste papillae. He went on to say (translation mine):
"...not all tongues are equally endowed [with papillae]; such that one tongue may have three times more than another. This circumstance explains why, when two dinner guests sit down to the same banquet, one experiences deliciousness, while the other seems to be eating under duress: it's that one of them has a tongue that is poorly equipped, and that the empire of flavor has its blind and deaf people."I'm not sure that taste-blind is a term I would use for a person who has relatively few fungiform papillae. Those of you who have few papillae can certainly taste something; it's just that what you taste is not as clearly defined nor is it as intense as it is for those of you with a greater number. I prefer the term "mildly sensitive taster," and reserve the term "taste-blind" for the inability to taste specific compounds...
...as in taste-blind to 6-n-propylthiouracil (PROP). The genetics of the ability to taste this bitter compound has been studied intensively, but has been complicated by the fact that you need not only a specific functional bitter receptor, TAS2R38, but also a sufficient number of fungiform papillae.
Tomassini-Barbarosa and colleagues at the University of Cagliari, Monserrato, Italy, have been studying a zinc-dependent compound in saliva, called gustin and also known as carbonic anhydrase VI (CA6), that is critical for the abundance, growth, shaping, maintenance, and survival of fungiform papillae on the tongue. They teamed up with Beverly Tepper from Rutgers University, New Jersey to explore the interactions between gustin function and PROP tasting.
The gene for gustin has two variants, one of which yields a functional protein, and the other a protein that binds zinc less effectively, and yields fewer papillae. Furthermore, these papillae are misshapen.
Here's my interpretation of the data presented by these authors. If you lack the gene variant of TAS2R38 that gives you the ability to taste PROP, you will not be able to taste it, no matter how many taste papillae you have.
However, if you do have the gene variant that imparts the ability to taste PROP, then the intensity you experience will be a function of the number of papillae you have, which in turn is dependent on gustin.
If you don't have any copy of the functional gustin gene, you will have few papillae, and PROP will taste weak. If you have one allele of the functional version of the gustin gene and one of the less functional one, you have an intermediate number of papillae. If you have two alleles of the functional gustin gene, as I do, you will have an abundance of papillae.**
The pictures below, from my lab, show tongues stained with blue food coloring. Fungiform papillae do not stain, so stand out against the blue background.
This top picture shows a tongue with few papillae, which are more oval than round. Although you can't see it in this illustration, the original photo shows few taste pores in these papillae. Though I don't have any genetic data (it was unavailable at the time we took this picture), we know that this person was a mildly sensitive taster, who was furthermore taste-blind to PROP.
This next picture shows the tongue of someone we dubbed a moderately sensitive taster, who could taste PROP, and for whom food was of great interest and generally felt to be delicious when well prepared. However, no flavor was too intense for this person.
Finally, this tongue is from someone (me, actually) for whom flavors can become easily too intense, and for whom the taste of PROP is beyond foul. The blue stain only appears slightly and further back in the tongue, while the front is carpeted with papillae. We called people in this category highly sensitive tasters. As I mentioned above, I have two alleles of the functional version of gustin, and this is the result.
Though I wouldn't be surprised if there were more factors involved to yield such an abundance of papillae.
More to come about the genetics of the taste and smell system and what they mean for your own experiences.
* Melania Melis, Elena Atzori, Stefano Cabras, Andrea Zonza, Carla Calò, Patrizia Muroni, Mariella Nieddu, Alessandra Padiglia, Valeria Sogos, Beverly J. Tepper, and Iole Tomassini Barbarossa. The Gustin (CA6) Gene Polymorphism, rs2274333 (A/G), as a Mechanistic Link between PROP Tasting and Fungiform Taste Papilla Density and Maintenance. PLoS One. 2013; 8(9): e74151. Published online 2013 Sep 9.
** Had me tested for several taste sensitivity markers, and this is one result.
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