Izaäk van der Horst was a son of Karel Simon van der Horst and ReintjeTurksma. He married 7 April 1929 in Amsterdam to Johanna Geertruida Velderman, from whom he was divorced on 25 November 1931.
Izaak was born in a family with seven children, of whom three children have survived the war. His other siblings, Meijer, Alida and Simon have been killed during the Holocaust.
City Archive of Amsterdam, …