Asparagine plasma concentration

The neutral amino acids alanine, serine, threonine, asparagine, glutamine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, histidine and citrulline share a common transporter at the luminal border of the epithelial cells in the renal tubuli and the epithelial cells in the small intestine [16]. In Hartnup disorder an impairment of this transporter leads to hyperexcretion of these neutral amino acids and to intestinal malabsorption. Excretion of tryptophan metabolites kynurenine and N-methyl-nico-tinamide is reduced. Plasma concentrations of the affected amino acids may be low normal or reduced. The inheritance is autosomal recessive. The hph2-deficient mouse has been postulated as a model for Hartnup disorder [17]. Affected persons may be asymptomatic, while some demonstrate pellagra-like photodermatitis or cerebellar ataxia due to a nicotinamide deficiency and respond well to the administration of nicotinamide [16]. 

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