A mental patient was arrested after his mother was strangled in their Sau Mau Ping flat yesterday. Chan Fok-ming, 63, called 999 at about 7am saying his mother had collapsed in their Lok Wah South Estate flat. Chan, an outpatient at Kowloon Hospital's psychiatric department, answered the door to police, who found Lau Kwei-chun, 88, unconscious in the lower deck of a bunk-bed with a bruised neck. Lau was pronounced dead at United Christian Hospital. She had Parkinson's disease and had trouble walking. Both lived on welfare. Kowloon Hospital said a community psychiatric nurse visited the man regularly. The last visit had taken place in the past week.