Which is the youngest patient with an abnormal anti-ribonuclear protein level? Please list his or her date of birth.
youngest patient refers to MAX(Birthday); abnormal anti-ribonuclear protein level refers to RNP NOT IN('-', '+-'); date of birth refers to Birthday;
SELECT T1.Birthday FROM Patient AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID WHERE T2.RNP != '-' OR '+-' ORDER BY T1.Birthday DESC LIMIT 1