A big increase in the issuance of residential mortgage backed securities in 2013 has contributed to healthy growth in funds under administration at Perpetual's corporate trust division.Perpetual Corporate Trust, which is the dominant provider of trustee services in the securitisation market, contributed A$10.5 million of pre-tax profit to Perpetual's group earnings in the six months to December - an increase of 22.1 per cent over the previous corresponding period.Issuance of residential mortgage backed securities was up 90 per cent in 2013, compared with 2012. Perpetual's securitisation funds under administration rose from $248.5 million at the end of December 2012 to $294.2 million at the end of the latest half.A highlight for the division was an increase in its margin on revenue to 42 per cent, up from 34 percent in the previous corresponding period.The higher margin was a result of the group divesting two low margin mortgage processing and servicing businesses.The group's 45 per cent stake in MARQ, an analytical services business designed for issuers and investors in the securitisation market, is no longer having a negative impact on revenue but is yet to make a profit.In December, Perpetual completed the acquisition of Trust Company. As the integration of the business gets underway corporate trust funds will be transferred to Perpetual Corporate Trust. This will boost corporate funds under administration by 59 per cent.