Editor—Ascorbate or vitamin C (VC) is an essential reducing agent and antioxidant that participates in a variety of metabolic processes.1 Unlike rodents and other animals, humans depend on dietary intake of VC to meet their daily requirement.1 2 VC intracellular accumulation is mediated through two distinct pathways. In one pathway, vitamin C is transported as such by high affinity sodium dependent carriers. In a second pathway, oxidised vitamin C (dehydroascorbic acid) is transported on glucose transporters GLUT1 and GLUT3.3 4

Recently the coding sequences of the human Na⁺ dependent VC transporters types 1 and 2, hSVCT1 and hSVCT2, products of theSLC23A2 andSLC23A1 genes, respectively, were identified.5-7 Both genes were first identified as anonymous expression sequence tags (ESTs).8 9Subsequently, and based on homology, humanSLC23A2 andSLC23A1 were identified as nucleobase transporters YSPL3 andYSPL2, respectively.10 Their full length coding sequences, expression profile, and function were then identified.5-7 The EST location ofYSPL3 and the physical location of theSLC23A2 gene on chromosome 5 were also recently confirmed.6 8-10

The known enzymatic roles of VC in collagen hydroxylation, carnitine biosynthesis, formation of the catecholamine norepinephrine, and as an inhibitor of oxidation make both SLC23A2 andSLC23A1 candidate genes for a variety of human disorders.1 2 These may include monogenic diseases affecting the skeleton, fat metabolism, and the endocrine glands, as well as polygenic conditions, such as osteoporosis, obesity, hypertension, and aging. Thus, the knowledge of the precise genetic and …