Magento Sorting by category custom attribute

      $categories = Mage::getModel('catalog/category')->getCollection()
        ->addAttributeToFilter("show_on_home_page",1)
 ->addAttributeToSelect("name")
 ->addAttributeToSelect("description")
 ->addAttributeToSelect("catextra_description")
 ->addAttributeToSelect("catextra_order")
 ->addAttributeToSelect("thumbnail")
 ->addAttributeToSort('catextra_order', ASC);