I was recently contacted by a previously unknown fifth cousin, Andrea, from Bremen, Germany. We share fourth great-grandparents, Peter Joseph Mauren and Anna Maria Minwegen. Her branch of the family remained in Germany while my third great-grandparents emigrated to America in 1840.
It was quite common for our German ancestors to call their children by their middle names. In the same family, several children could have the same first name, such as Anna or Maria, or Johann. These children were known and called by their middle names. See for example my fifth great-grandparents, Peter and Christina Marx. They had four daughters having Anna as a first name: Anna Maria, Anna Margaretha, Anna Catharina, and Anna Gertrude.