Canto-pop diva Anita Mui Yim-fong had been diagnosed with an illness of the central nervous system, which could have impaired her mind and judgment, one day after she signed a disputed will at the hospital, a court heard yesterday. The oncologist who treated the star until she died told the Court of First Instance that Mui might have suffered a milder form of the disease that he failed to detect clinically when she signed a will to set up a trust for her estate on December 3, 2003. Peter Teo, of the Hong Kong Sanatorium and Hospital, an attesting witness to the will, stood by his assessment that Mui was mentally sound to make a will until she fell into a coma on Christmas Eve the same year. But his assessment relied solely on 'common sense' and the clinical diagnosis was challenged by Mui's mother, Tam Mei-kam, 84, who disputes the validity of the will, questioning her mental capacity to do so in a probate action before the court. The will left the late singer's entire estate, estimated to be worth HK$100 million, in a trust to be managed by HSBC because Mui feared her mother would squander it. The trust provides her mother with a monthly allowance of HK$70,000. The star died of cervical cancer on December 30, aged 40. Dr Teo said he noted Mui's interrupted speech, dull mental state and dizziness on the morning of December 4. This triggered more tests. He then confirmed on the same day that the star suffered from hepatic encephalopathy after a test indicated a high ammonia level in her blood content, which could also have affected her mind. The ammonia level might also have started to affect her mind as early as 7am on the day. The doctor said it was possible that a milder form of the disease might have been present before it became clinically obvious. But he said the star was able to ask and respond appropriately to questions in his presence during a meeting when she signed the will. Hepatic encephalopathy is a syndrome that damages the brain and nervous system due to acute or chronic liver dysfunction. This could affect a patient's thinking. Chan Chi-hung SC, for Ms Tam, asked why the doctor did not conduct independent neurological and psychological tests to establish the singer's mental state. Based on observations by himself and a team of doctors, Dr Teo said Mui remained mentally sound, sociable and keen to talk during ward rounds until Christmas Eve. Dr Teo's cross-examination continues today.