Robert M. Cohn

Urinary citrate excretion in the diagnosis of distal renal tubular acidosis

Since hypocitraturia in distal renal tubular acidosis, we screened the asymptomatic children in three families with familial dRTA, by comparing their 24-hour urine citrate excretion to values obtained in 45 normal children. Subsequent acid loading uncovered four new cases of dRTA suspected because of the finding of hypocitraturia. Because hypocitraturia probably contributes to nephrolithiasis/nephrocalcinosis and subsequent renal damage in dRTA, affected family members were treated with alkali (4 mEq/kg/day), which normalized urine citrate in three children; in a fourth child citrate excretion rose but was not normal. Measurement of urine citrate excretion was superior to other currently proposed screening tests for dRTA (first morning urine pH and sediment, urine concentration).

Beta-methylcrotonic aciduria associated with lactic acidosis

A patient is described in whom lactic acidosis of very severe degree was found to coincide with the presence of beta-methylcrotonic acid and rho-hydroxyphenyllactic acid in urine in large amounts, while beta-hydroxyisovaleric acid was found to be a relatively minor excretion product. Beta-methylcrotonic acid is demonstrated, for the first time, to be present in blood and CSF. These findings are discussed in relation to the patients previously reported to have beta-methylcrotonylglycinuria and raise the possibility that our patients organic aciduria may be secondary to acquired disease rather than to an inborn error of metabolism.

Isovaleric acidemia: use of glycine therapy in neonates.

ISOVALERIC acidemia is an inborn error of leucine metabolism caused by a deficiency of isovaleryl-coenzyme A dehydrogenase.1 , 2 Affected patients are usually seen during the neonatal period with a...

Some characteristics and developmental aspects of rat uridine diphosphogalactose 4-epimerase

Abstract UDP-Gal 4-epimerase (EC 5.1.3.2) activity in developing rat liver, gut, kidney and brain was studied. The assay involved the thin-layer chromatographic separation of sugar nucleotides on polyethyleneimine-impregnated cellulose. UDP-[ 14 C]Gal, the substrate, was converted to UDP-[ 14 C]Glc by the epimerase reaction. Since both the reactant and the product have the same R F value, the UDP-Glc is converted by UDP-Glc dehydrogenase to UDP-GlCUA which is easily distiguished from the UDP-Gal on these plates. Differential centrifugation localized epimerase activity from newborn and adult rat liver in the soluble fraction. Newborn liver had greater specific activity than any other tissue examined, while adult gut had the highest activity of any adult tissue. The activity of the newborn liver declined at Day 2, remaining at the same level until Day 16 when a precipitous decline to adult levels of activity by Day 20 occured. Brain and kidney had lower specific activity than found in liver. No differences in activity of liver enzyme were noted between male and female newborn or adults. The newborn enzyme had a υ max five times greater than the adult, but both enzyme preparations had the same (a) stability characteristics, (b) K m values for UDP-Gal (0.153 mM) and for UDP-Glc (0.5 mM), (c) pH optimum (8.3–8.65) and (d) requirement for exogenous NAD + . Further, both were inhibited by NADH, p -chloromercuribenzoate, UDP-Man, UMP and TDP-Glc, and both exhibited product inhibition with UDP-Glc.

Evaluation of the binding of serotonin by isolated CNS acidic lipids

Binding of serotonin by rat lipids was examined in an organic solvent-aqueous partition system. Only phospholipids and sulfatide were found to have appreciable activity: this technique was unsuitable for gangliosides due to their poor extractibility. Binding by phospholipid was abolished and that by sulfatide was greatly inhibited by increasing ionic strength in the aqueous phase. At an ionic strength of 0.3 M the apparent affinity of sulfatide for serotonin was about 3×103 M. Both tryptamine and 5-methoxytryptamine were much more effective than serotonin in inhibiting the binding of radioactive serotonin, suggesting that the observed binding is simply a charge neutralization with little specificity. Binding of serotonin by mixed brain gangliosides was examined in an equilibrium dialysis system. Without adequate precautions, the chemical lability of serotonin was found to produce spurious data when binding was assessed by the distribution of radiolabel. Binding of serotonin by ganglioside was also greatly inhibited by increasing ionic strength: at 0.3 M an apparent affinity of about 103 M was found. While dopamine did not inhibit the binding of radioactive serotonin, tryptamine, 5-methoxytryptamine, and serotonin were equally effective inhibitors.

On the involvement of serotonin in galactose brain toxicity.

MENTAL retardation is frequently a consequence of the biochemical toxicity associated with human inborn errors of metabolism. Galactosemia, due to a defect in the enzyme galactose-1-phosphate uridylyltransferase, was one of the first of such syndromes to be delineated (SEGAL, 1978). The recognition of the relationship of abnormal galactose metabolism to brain dysfunction has been the stimulus for numerous investigations into the underlying biochemical events (WELLS, 1969; HAWORTH et al., 1969, 1970; WARFIELD & SEGAL, 1978). Since there is no genetic animal counterpart for the human condition, the model employed has involved the feeding of high galactose diets which overwhelms the capacity of normal animals to metabolize the sugar. In rats this results in a constellation of abnormalities resembling the human galactosemic condition (CRAIG & MADDOCK, 1953; ROSENBERG et al., 1961; SPATZ & SEGAL, 1965). WOOLLEY and his co-workers in a series of publications (WOOLLEY & GOMMI, 1964, 1965; WILD et al., 1967) implicated defective serotonin receptor reactivity in developing rats fed a high galactose diet as the basis of brain dysfunction. These workers reported that the contracture of stomach strips from galactose toxic rats in response to serotonin was diminished (WOOLLEY & GOMMI, 1964). Furthermore, brains from galactose toxic rats were found to be deficient in a ganglioside present in normal brain which restored the sensitivity of neuraminidase treated stomach strips to serotonin (WILD et al., 1967). High affinity binding for serotonin specific to the central nervous system of normal animals which was destroyed by neuraminidase has been described (MARCHBANKS, 1966). Recently, the high affinity uptake of serotonin by brain subcellular particles, which is also sensitive to neuraminidase, has been reported (DETTE & WESEMANN, 1978). In this report, we have examined the implications of the works of WOOLLEY and co-workers, that there may be a deficiency of sialic acid containing serotonin receptors in brain of galactose toxic animals, from two points of view. First, to substantiate the previous findings, we have performed a chemical analysis of brain gangliosides and galactolipids from normal and galactose toxic rats. Second, we have measured the uptake of radioactive serotonin by synaptosomes from galactose fed animals as a more direct assessment of nervous system toxicity than the contraction response of stomach strips to serotonin.