Database: thrombosis_prediction
Question: Among the patients with a normal Ig G level, how many of them have symptoms?
SQL: SELECT COUNT(T1.ID) FROM Patient AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID INNER JOIN Examination AS T3 ON T3.ID = T2.ID WHERE T2.IGG BETWEEN 900 AND 2000 AND T3.Symptoms IS NOT NULL