Bank and thrift holdings of mortgages were higher in the first quarter of 2013 compared to a year ago, driven by originations of nonconforming loans. While two banks have started to securitize jumbo mortgages, the vast majority of jumbo originations remain in portfolio. Bank holdings of first-lien mortgages hit $1.78 trillion at the end of the first quarter of 2013, up 2.2 percent from the first quarter of 2012, according to a new ranking and analysis by Inside Nonconforming Markets ... [Includes one data chart]