Complex sentence: Mackie writes that FGM is found only in or adjacent to Islamic groups, but is not practised in most Muslim countries or in Mecca or Medina, Islam's holiest cities, where the Saudis regard it as a pagan custom.
Split into simpler sentences: Mackie writes that FGM is found only in or adjacent to Islamic groups, but is not practised in most Muslim countries. It is also not practised in Mecca and Medina, Islam's holiest cities, where the Saudis regard it as a pagan custom.