Supercharged growth in its mortgage book remains a pillar of the Macquarie Group story, with the Australian mortgage portfolio of its banking arm expanding by five per cent to A$34.3 billion over the June 2018 quarter.That's 20 per cent annualised and in line with growth reported in the monthly APRA data for Macquarie Bank on both a three month (to May 2018) and six month basis.Macquarie Bank is one of the lenders that has bumped up interest rates on variable mortgages in recent weeks, but even so there's "pressure due to higher costs" on the bank's net interest margin, Nicholas Moore, the group's managing director told the annual meeting in Sydney yesterday.Steering the risk trade-offs on a fast growing balance sheet business - four times the growth of system - is a task Moore will soon pass to his successor as CEO.Macquarie Group used its annual meeting as the occasion to announce that Nicholas Moore will step down at the end of November.Shemara Wikramanayake, currently head of Macquarie Asset Management, and a 30-year veteran of the bank, will take over in his place.One task for Moore in the final days of his tenure will be to front the royal commission into misconduct in the banking, superannuation and financial services industry, which by then will be conducting its seventh round of hearings focusing on policy considerations arising from the first six rounds. Moore "will be called to give evidence," the annual meeting was told.