Cherubism may sound angelic, but it certainly is not. The rare bone disorder afflicts children starting at about age 3 or 4, causing them to develop chubby cheeks and upward-looking eyes like those of a cherub. It is not known how many people have the disorder; about 200 cases have been described in the medical literature. Symptoms usually recede after puberty, and children with mild forms of cherubism generally appear normal as adults. However, in its severe forms, cherubism can lead to excessive destruction of the jawbone. Many victims of the disorder have difficulty chewing because of reduced jaw movement. Now, Harvard Medical School researchers have identified the mutant gene responsible for cherubism. They hope that their research may lead to ways to treat cherubism or avert it, and they think that prenatal diagnosis of the condition may one day be possible. They also hope to gain greater understanding of much more common bone ailments such as osteoporosis.