Stature and nutrition in cystinuria and Hartnup disease

Intestinal Amino Acid Transport and Metabolic Health

Amino acids derived from protein digestion are important nutrients for the growth and maintenance of organisms. Approximately half of the 20 proteinogenic amino acids can be synthesized by mammalian organisms, while the other half are essential and must be acquired from the nutrition. Absorption of amino acids is mediated by a set of amino acid transporters together with transport of di- and tripeptides. They provide amino acids for systemic needs and for enterocyte metabolism. Absorption is largely complete at the end of the small intestine. The large intestine mediates the uptake of amino acids derived from bacterial metabolism and endogenous sources. Lack of amino acid transporters and peptide transporter delays the absorption of amino acids and changes sensing and usage of amino acids by the intestine. This can affect metabolic health through amino acid restriction, sensing of amino acids, and production of antimicrobial peptides.

Sulfur amino acid metabolism in cystinuria: a biochemical and clinical study of patients

Sulfur amino acid metabolism was studied in 26 homozygotic cystinuric patients, some of whom received D-penicillamine, 2-mercaptopropionylglycine or N-acetylcysteine treatments in order to evaluate signs of cyst(e)ine deficiency. Decreased leukocyte glutathione and taurine levels, plasma cyst(e)ine and taurine concentrations and urinary inorganic sulfate, taurine, mercaptolactate and thiosulfate outputs were found in cystinuric patients, probably reflecting intracellular cyst(e)ine deficiency. An increased mercaptoacetate-cysteine mixed disulfide output was found, probably as result of a poor tubular reabsorption of this compound, as well as for cystine. Normal retinal function was recorded in all patients. During drug treatments, the excretion of most of the sulfur compounds in cystinurics was as those found in controls, probably reflecting an increased mobilization of cysteine. N-acetylcysteine treatment increased the excretion of cyst(e)ine and can thus not be recommended as stone preventive therapy in cystinuria.

The Hartnup phenotype: Mendelian transport disorder, multifactorial disease

The Hartnup mutation affects an amino acid transport system of intestine and kidney used by a large group of neutral charge alpha-amino acids (six essential and several nonessential). We compared developmental outcomes and medical histories of 21 Hartnup subjects, identified through newborn screening, with those of 19 control sibs. We found no significant differences in means of growth percentiles and IQ scores between Hartnup and control groups (but all low academic performance scores were found in the Hartnup group, and various skin lesions occurred in five Hartnup subjects), no significant difference between means of the summed plasma values for amino acids affected by the Hartnup gene in Hartnup and control groups, two Hartnup subjects with clinical manifestations--impaired somatic growth and IQ in one, impaired growth and a "pellagrin" episode in the other--who had the lowest summed plasma amino acid values in the Hartnup group; the corresponding values for their sibs were the low outliers in the control group, and two tissue-specific forms of the Hartnup (transport) phenotype: renal and intestinal involvement (15 families) and renal involvement alone (one family), both forms having been inherited as autosomal recessives (the symptomatic probands had the usual form). Whereas deficient activity of the "Hartnup" transport system is monogenic, the associated plasma amino acid value (measured genotype) is polygenic. The latter describes the parameter of homeostasis and liability to disease. Cause of Hartnup disease is multifactorial.

Pregnancy and cystinuria

46 pregnancies in patients with cystinuria treated with a high fluid intake alone or in combination with D-penicillamine resulted in 41 normal births. New stones formed in 18 pregnancies, with stone passage early in 4 of them. No patient required stone removal during pregnancy. Other pregnancy-related problems included hypertension and urinary-tract infection, which responded to conventional management. Assiduous maintenance of a sustained high fluid intake is even more important than usual during pregnancy and the puerperium. D-penicillamine appears relatively safe for severe cases, although most patients can be managed without it. With careful medical management stone-forming cystinurics can be safely conducted through pregnancy without increased risks to the mother or fetus.

Childhood cystinuria in New South Wales. Results in children who were followed up after being detected by urinary screening in infancy

Homozygous cystinuria was diagnosed in 45 children and 19 of their siblings in the course of routine urine screening of 6-week-old infants in New South Wales. These children were followed for up to 14 years. During this time there were 5 clinical episodes of renal disease which could be ascribed to cystinuria. There was normal mental development in all the children except one. Of 49 children over 3 years, 4 had height centiles less than the midparent height centile, while 45 had height centiles equal to or above the midparent centiles. Family testing in these 45 cases showed that 60% were type I cystinurics, and 35% were of the mixed or compound type (5% were not classified). Data from the parents and grandparents showed that renal tract calculi had occurred in 14 of them. This study shows that children with homozygous cystinuria, detected by urinary screening in infancy, rarely have renal symptoms. Mental development was normal as was growth in height. There was an increased incidence of noncystine stone formation among the relatives of these children. The incidence of homozygous cystinuria in New South Wales in one in 17 286.

Natural history of Hartnup disease

Hartnup disease was diagnosed in 12 children and 3 of their 15 sibs in the course of routine urine screening of 6-week-old infants in New South Wales. These children were followed for up to 8 years, during which time there were only two clinical episodes which might be ascribed to Hartnup disease. The mental development of all the children was normal. 10 had height centiles less than the midparent height centiles, while 4 had centiles equal to or above the midparent centiles. The study shows that in children with Hartnup disease in Australia symptoms are very uncommon. Mental development is normal, and heights are possibly slightly below that expected. Hartnup disease has an incidence of approximately 1 in 33 000 in New South Wales.

Cystinuria and its relationship to mental retardation

Urine specimens from 2,073 mentally retarded children have been analysed for their amino acid content, with the aim of determing the relationship of cystinuria and mental retardation. No children homozygous for cystinuria were identified, but 50 heterozygous children were found. This heterozygote incidence is 13 times that expected in our general population.

Amino acid imbalance in cystinuria

After oral ingestion of a free amino acid mixture by three cystinuric patients, plasma increments of lysine and arginine were lower and those of many other amino acids were significantly higher than those found in control subjects. Similar results were obtained in control subjects after amino acid imbalance had been artificially induced by the omission of cystine, lysine, and arginine from the amino acid mixture. Especially high increments of alanine and proline provided the best evidence of amino acid imbalance caused by a temporary lysine and, to a lesser extent, arginine and cystine deficit. No such amino acid imbalance was found to occur in the cystinuric patients after ingestion of whole protein, indicating that absorption of oligopeptides produced by protein digestion provided a balanced physiological serum amino acid increment. This is considered to explain the lack of any unequivocal nutritional deficit in cystinuric patients despite poor absorption of the essential free amino acid, lysine.

Studies on intestinal absorption of amino acids and a dipeptide in a case of Hartnup disease

A severely affected case of Hartnup disease is reported, where the patient responded rapidly to nicotinamide. This supports the view that all the clinical features, except reduced stature from general nutritional defect, are secondary to tryptophan and nicotinamide deficiency rather than to an unknown toxic factor. Severe malabsorption of both tryptophan and phenylalanine was demonstrated. The dipeptide carnosine was absorbed normally whereas when the two constituent amino acids, beta-alanine and L-histidine, were ingested, absorption of the former was normal but that of the latter was grossly defective. The suggestion is advanced that in cases of Hartnup disease protein nutrition is maintained by intestinal uptake of amino acids as oligopeptides rather than as free amino acids. By contrast, both modes of absorption are probably important in normal subjects. Radiology of the small intestine is abnormal in Hartnup disease when a large amount of protein is admixed with the barium meal.

Cystine stones treated by surgery and D-penicillamine

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