Inherited defects in amino acid transport at the cell membrane are usually expressed as selective renal amino aciduria, i.e., the concentration of the affected amino acids is high in the urine while it is normal or low in plasma. Intestinal absorption of the affected amino acids is also almost always impaired. The clinical symptoms thus result from excess amounts of certain amino acids in the urine or lack of them in the tissues. There are systemic and non systemic disorders. Non systemic disorders with normal plasma AA include cystinurias in which renal stones may be formed because of high urinary concentration of poorly soluble cysteine, and iminoglycinuria and dicarboxylic aciduria that are mostly asymptomatic. There are 4 systemic disorders with low plasma AA. In lysinuric protein intolerance (LPI), the transporter defect for the dibasic cationic amino acids leads to poor intestinal absorption and urinary loss of arginine, ornithine and lysine. Subsequently, the patients develop protein intolerance with hyperammonaemia, growth retardation and skeletal and immunological manifestations. SLC6A19 and collectrin deficiency are responsible for Hartnup disease (neutral amino acids with secondary niacin deficiency), and Hartnup like disorder (neutral and acidic amino acids) respectively and may present with postnatal multisystemic manifestations. The pellagra-like dermatitis and ataxia are attributed to deficiency of tryptophan, the precursor of niacin synthesis. An IMD linked to brain carrier defects of essential AA is caused by mutations in SLC7A5, resulting in the defective brain transport of branched chain AA (BCAA) responsible for a severe neurodevelopmental disorder.