The researchers conducted cell culture experiments using techniques to trace the interaction of the proteins, which revealed that together the Norrin and Fz4 proteins activate a key development pathway called the Wnt pathway. The two components also required a third co-receptor called Lrp5, which is known to be key to Wnt signaling, said Nathans.

The cell culture experiments also revealed that the Norrin protein was a key trigger for the Fz4 receptor, selectively binding to it and activating it. Importantly, we found this to be very high-affinity, highly specific binding, noted Nathans.

Further, the researchers studied two human forms of FEVR, finding that in patients with the disorder, mutations in the Frizzled-4 gene interfered with Norrin-dependent signaling.

If reduced activity of the Norrin signaling pathway is in fact the underlying cause of the two disorders, Nathans said, a drug that increases that activity could be helpful. Such a drug might also be effective in treating diseases that occur later in life in which the Norrin-Fz4 system might play some role, such as diabetes and age-related macular degeneration, Nathans added. Similarly, a condition known as retinopathy of prematurity, in which premature infants treated with high oxygen levels because of their undeveloped lungs subsequently suffer abnormal retinal vascular development, might also be benefited.

Since the Norrin-Fz4 pathway is specific to the eye, a drug that manipulates that system might be able to treat these disorders without many side effects, a significant improvement over drugs that more generally affect vascular growth, Nathans said.

However, emphasized Nathans, far more work needs to be done to understand the role of the Norrin-Fz4 pathway in vascular development. We're not sure how much this pathway generalizes, he said. In fact, we don't know very much about vascular development in general. It's a fascinating and provocative question of why nature went to the trouble of evolving a specific pathway just to build these vessels in the eye and the inner ear. It hints that there may be other specialized vascular development systems in other tissues and organs.