They are called Allomantic savants. Men or women who flare their metals so long, and so hard, that the constant influx of Allomantic power transforms their very physiology.
In most cases, with most metals, the effects of this are very slight. Bronze burners, for instance, often become bronze savants without knowing it. Their range is expanded from burning the metal so long. Becoming a pewter savant is dangerous, as it requires pushing the body so hard in a state where one cannot feel exhaustion or pain. Most accidentally kill themselves before the process is complete, and in my opinion, the benefit isn't worth the effort.

Tin savants, however . . . now, they are something special. Endowed with senses beyond what any normal Allomancer would need—or even want—they become slaves to what they touch, hear, see, smell, and taste. Yet, the abnormal power of these senses gives them a distinct, and interesting, advantage.

One could argue that, like an Inquisitor who has been transformed by a Hemalurgic spike, the Allomantic savant is no longer even human.