Observations on nicotinic acid therapy in Hartnup disease.
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The mother and daughter in a family had homozygous cystinuria and were also heterozygous carriers of the oculo-cerebro-renal dystrophy of Lowe. The daughter was also epileptic. The son had Lowe's syndrome and the father an increased urinary excretion of cystine and lysine. This evidence together with other case reports suggests that the defect in cystinuria and that of Lowe's syndrome may be connected.
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Lysinuric protein intolerance (LPI) is an autosomal recessive defect of diamino acid transport characterised by massive diaminoaciduria, especially lysinuria, with hyperammonaemia after heavy nitrogen intake. The defect has previously been demonstrated in the kidney, and is probably present in the liver cells. To evaluate the effect of the LPI gene on the net intestinal absorption of the diamino acids and citrulline, separate oral loads of each were given to controls, and to subjects heterozygous and homozygous for LPI. In the affected subjects the plasma concentrations of the loaded diamino acids showed lower increments after the loads than in the controls, the difference being marked in the homozygotes and moderate in the heterozygotes. Urinary excretion failed to explain these differences. Thus, the diamino acid transport defect of LPI is also present in the intestine. After citrulline loads, in contrast, plasma citrulline levels rose similarly in controls and homozygotes. Thus, LPI is associated with intact citrulline absorption. The ornithinopenic hyperammonaemia of LPI is probably preventable by supplementing dietary protein with the ornithine precursor citrulline.
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In lysinuric protein intolerance (LPI), impaired transport of cationic amino acids in kidney and intestine is due to mutations of the SLC7A7 gene. To assess the functional consequences of the LPI defect in nonepithelial cells, we have characterized cationic amino acid (CAA) transport in human fibroblasts obtained from LPI patients and a normal subject. In both cell types the bidirectional fluxes of arginine are due to the additive contributions of two Na(+)-independent, transstimulated transport systems. One of these mechanisms, inhibited by N-ethylmaleimide (NEM) and sensitive to the membrane potential, is identifiable with system y(+). The NEM- and potential-insensitive component, suppressed by L-leucine only in the presence of Na(+), is mostly due to the activity of system y(+)L. The inward and outward activities of the two systems are comparable in control and LPI fibroblasts. Both cell types express SLC7A1 (CAT1) and SLC7A2 (CAT2B and CAT2A) as well as SLC7A6 (y+LAT2) and SLC7A7 (y+LAT1). We conclude that LPI fibroblasts exhibit normal CAA transport through system y(+)L, probably referable to the activity of SLC7A6/y+LAT2.
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315 mentally retarded children from the coastal districts of Andhra Pradesh, south India, were screened to detect metabolic defects. Results with 2 cases of Hunter's syndrome, 1 case of Sanfilippo's syndrome and an unusual case of hyperamino aciduria are presented.
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Fifteen patients with artificial heart valves and evidence of chronic intravascular haemolysis were studied for proximal tubular dysfunction. Three patients had haemosiderinuria and haemoglobinuria; 2 had haemoglobinuria alone. Increased urinary amino acid nitrogen occurred in 8, raised fractional beta 2-microglobulin excretion in 2, hypophosphataemia in 4, renal glycosuria in 1 and enhanced fractional urate excretion in 1. Urinary N-acetyl-beta-glucosaminidase (NAG) excretion increased in 7; the mean urinary NAG/creatinine ratio was raised to twice the upper limit of the normal range. Renal haemosiderosis due to chronic intravascular haemolysis could cause tubular injury.
Nephrocalcinosis was described in preterm infants by several authors who tried to determine its association with hypercalciuria and furosemide therapy. We evaluated these potential mechanisms along with other lithogenic factors not previously studied in 10 premature babies. Hypercalciuria was an inconsistent finding like in other reports; elevated uric acid excretion and hyperoxaluria were observed in 5 and 6 cases, respectively. The aminocid excretion was normal in all infants. Our data suggest that in addition to hypercalciuria, other lithogenic factors may play a role in the pathophysiology of nephrocalcinosis of premature infants.