Further to my post: St Ismeria - Greatgrandmother of Jesus comes this article from AOL - Scholar uncovers legend of Jesus' greatgrandmother:
The story of Ismeria was discovered by Catherine Lawless, a history lecturer at Ireland's University of Limerick, in two manuscripts from 14th- and 15th-century Florence, Italy. But while it's tempting to believe that these recently unearthed papers shed new light on the Virgin Mary's family, Lawless told AOL News that, just like "The Da Vinci Code," the tale is almost certainly a work of fiction.
There is no biblical-era evidence to support the manuscripts' assertion that Ismeria was the mother of St. Anne, who later gave birth to Mary. (Other medieval sources suggest Ismeria may have been Anne's sister). Instead, Lawless suspects that the story may have been created by a religious order as a "morality tale" intended to teach Florentine women how to be good wives, and later, widows.