Second-tier lenders maintained growth in their mortgage books over the past three months, despite flat conditions in the market overall. The Australian Prudential Regulation Authority reported last week that there was little growth in the big four banks' mortgage portfolios in the September quarter. However, Citibank, Suncorp Bank, AMP Bank, Bendigo and Adelaide Bank, Macquarie Bank, bankmecu and Teachers Mutual Bank all recorded growth rates of one per cent or more for the quarter.Suncorp led the way, with 2.5 per cent growth in its mortgage portfolio during the quarter. Citibank was up two per cent and AMP Bank was up 1.9 per cent.Among the big banks, NAB maintained above-system growth despite giving up much of its mortgage pricing lead this year. Its mortgage book increased 1.2 per cent over the quarter.ANZ was up 0.1 per cent and Westpac (including St George) was up 0.8 per cent. CBA's book shrank 2.1 per cent, but it made a revision to its data last month, moving a substantial chunk of its loan from the mortgage category to business loans. Among those that suffered shrinkage in their mortgage portfolios were ING Direct, Rabobank, ME Bank, Arab Bank and Beirut Hellenic Bank.