Former Singapore Prime Minister Lee Kuan Yew (LKY) makes a point as he speaks during the LKY School of Public Policy 7th anniversary dialogue session in Singapore in this September 14, 2011 file photo. [Photo/Agencies]

SINGAPORE — Former Singapore Prime Minister Lee Kuan Yew has a rare nerve disease that makes walking difficult, his daughter said Sunday.

Lee, who led Singapore from 1959 to 1990, has been diagnosed with sensory peripheral neuropathy, a disease that affects nerves outside the central nervous system and undermines balance, Lee Wei Ling wrote in her weekly column in the Straits Times.

"On some days he is fairly steady and on other days his balance is poor," said Wei Ling, who is a medical doctor and director of Singapore's National Neuroscience Institute. "Being deprived of sensation from his legs means he finds it a challenge to balance."

The 88-year-old Lee's brain and muscles are working normally, and he's walking on a treadmill three times a day to improve his balance, Wei Ling said. Lee stepped down as a cabinet minister earlier this year but is still a member of parliament and frequently travels abroad to meet foreign leaders.

"I think with medication and simple precaution, he can continue to be of service to his country and the world," Wei Ling said.

Sensory peripheral neuropathy has a range of causes, and Wei Ling did not specify what may have caused her father's. She said she also suffers from the disease.

Lee became prime minister in 1959 and saw the country through self-rule under the British, a two-year federation with Malaysia and finally independence in 1965. He remained in office until 1990, overseeing a period of rapid development that turned Singapore from a sleepy port city into a modern, virtually corruption-free society that remains a darling of foreign investors.

Lee's son Lee Hsien Loong is the current prime minister.