ISLAMABAD: Jan 22 (INP) The National Accountability Bureau (NAB) filed in the accountability court on Monday a supplementary reference against former prime minister Nawaz Sharif and four others in the Avenfield properties case. Nawaz and his family face three references pertaining to the Azizia Steel Mills and Hill Metals Establishment, their London (Avenfield) properties, and over a dozen offshore companies, including Flagship Investment Ltd. INP/AH