Databinding problem with Datagrid and Inheriting Class

I have a class that is used as a datasource for a datagrid that
doesn't display properties that it inherits from another class. I have
a Item class that inherits from a CommonItem class properties. When I
create an object of an Item. It works fine.. it inherits all the
properties from CommonItem and has its own prperties. I can set/get
property from the inherited properties.. but when I try to display
with a datagrid by datasource = collection of item.. a collection of
the item object, all I get the the Item class properties ONLY and
nothing from the CommonItem properties.. Any got advice..