nytimes.com — The Vatican has appointed an American bishop to rein in the largest and most influential group of Catholic nuns in the United States, saying that an investigation found that the group has "serious doctrinal problems." The Vatican's assessment, issued on Wednesday, said that members of the group, the Leadership Conference of Women Religious, have challenged church teaching on homosexuality and the male-only priesthood, and promoted "radical feminist themes incompatible with the Catholic faith."