Method: Coding regions of AGAT, GAMT, and SLC6A8 (CT1) genes were sequenced on 25, 55, and 105 individuals, respectively. Results: Mutations in 3, 10, and 13 patients, respectively, were identified. The majorities (>70%) were novel, null mutations with an overall mutation detection rate of 14.2%, suggesting that biochemical and clinical diagnosis requires molecular confirmation.