Complex sentence: It is estimated that about 7,500 Italian Jews perished in the Holocaust, out of a pre-war Jewish population that amounted to 58,500 (46,500 by Jewish religion and 12,000 converted or non-Jewish sons of mixed marriages).
Split into simpler sentences: It is estimated that about 7,500 Italian Jews perished in the Holocaust. Italy's pre-war Jewish population was 58,500 (46,500 by Jewish religion and 12,000 converted or non-Jewish sons of mixed marriages).