Gene Defect Alters Ion Channel in Melanosomes to Cause Form of Albinism

A team led by Brown University biologists, together with colleagues, has discovered the way in which a specific genetic mutation appears to lead to the lack of melanin production underlying a form of albinism. Newly published research provides the first demonstration of how a genetic mutation associated with a common form of albinism leads to the lack of melanin pigments that characterizes the condition. Approimately 1 in 40,000 people worldwide have type 2 oculocutaneous albinism, which has symptoms of unusually light hair and skin coloration, vision problems, and reduced protection from sunlight-related skin or eye cancers. Scientists have known for about 20 years that the condition is linked to mutations in the gene that produces the OCA2 protein, but they hadn’t yet understood how the mutations lead to a melanin deficit. In the new research, a team led by Brown University biologists Nicholas Bellono and Dr. Elena Oancea shows that the protein is necessary for the proper functioning of an ion channel on the melanosome organelle (image), the little structure in a cell where melanin is made and stored. The ion channel is like a gate that lets electrically charged chloride molecules flow into and out of the melanosome. When the melanosome lacks OCA2 or contains OCA2 with an albinism-associated mutation, the researchers found, the chloride flow doesn’t occur and the melanosome fails to produce melanin, possibly because its acidity remains too high. The discovery could inspire new ideas for treating albinism, said Dr. Oancea, assistant professor of medical science and senior author of the paper published online on December 16, 2014 in the open-access journal eLife. “From a therapeutic point of view, we now have a channel that’s a possible drug target,” she said.
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