SELENBP1 has been reported to be involved in the development of several cancers, although its precise function has remained elusive until now. Now scientists have uncovered that autosomal recessive mutations in this gene lead to a novel error of metabolism that causes chronic bad breath due to elevated levels of sulfur-containing compounds. They were able to show for the first time that the protein encoded by SELENBP1 is a methanethiol oxidase and converts methanethiol to hydrogen peroxide, formaldehyde, and hydrogen sulfide. So far, methanethiol-degrading enzymes have not been known to exist in humans.

Chronic bad breath odor that originates from outside the mouth is most frequently caused by conditions affecting the nose, sinuses, tonsils and esophagus, but in some cases foul-smelling molecules, mainly dimethyl sulfide, are carried via the blood to the lungs and are then exhaled. In their recent study, the researchers identified inactivating mutations of the SELENBP1 gene in five patients with cabbage-like breath odor that primarily came from high levels of methanethiol and dimethyl sulfide. By functional analyses they showed that this metabolic defect was attributable to deficient enzymatic activity of methanethiol oxidase.

The results of their study have been published in Nature Genetics.