Researchers have identified a genetic association with facial asymmetry in an ancient cavefish, a natural trait that may solve mysteries surrounding facial asymmetries in humans  conditions such as cleft palate or hemifacial microsomia. This exciting discovery by Joshua Gross, a University of Cincinnati assistant professor for the Department of Biological Sciences; and doctoral students Amanda Krutzler and Brian Carlson, is published in the research journal, Genetics.

The researchers are studying the craniofacial features of the eyeless, cave-dwelling fish,

Astyanax mexicanus

, which has lived in the pitch-black caves of the Sierra de El Abra region of Mexico for millions of years. Theyre comparing those features with closely related sighted surface-dwelling fish that are found in Mexico, Texas and New Mexico.

These cavefish have no eyes, although they are acutely sensitive to sound and vibration. Despite being eyeless, they have several similar bony features in their eye regions compared to their sighted, surface- dwelling counterparts. These similarities allowed the researchers to directly compare traits in the surface-dwelling fish with the cavefish. The cavefish, however, appear drastically different since they are albino and nearly translucent, compared with the darker pigmented surface-dwelling fish.

The researchers are screening the genomes of every individual fish from a hybrid pedigree housed in their lab  looking for genes that may lead to variations in eye size or pigmentation.

In the cavefish, they discovered genetic markers on two separate chromosomes that are associated with extensive bone fragmentation on the right side of the skull. Although bone fragmentation also occurs on the left side of the skull, no genetic associations were detected when scoring on the left side of the cranium. The sighted surface-dwelling fish never demonstrated any of these craniofacial abnormalities.

By understanding how genes are behaving differently on the right versus the left sides, we hope to discover why many craniofacial alterations are more severe or present on only one side of the face in humans, says Gross.

Researchers are now narrowing in on the precise genes associated with these cranial abnormalities, with indications that two genes previously shown to be associated with cleft palate in humans,

bone morphogenetic protein number four (BMP4) and transforming growth factor beta family member 3 (TGFB3)

, may similarly be involved in natural forms of bone asymmetry.

Previous research discovered that the gene that causes red hair and pale skin in humans was the same gene that caused the albino-like cavefish to have less pigmentation than the surface-dwelling species.

Funding for the research was supported by a federal grant from the National Institute of Dental and Craniofacial Research, National Institutes of Health.