David E.C. Cole

Serum osteocalcin concentrations in children with metabolic bone disease

We surveyed both normal children and patient populations to identify the effects of metabolic bone disease and impaired renal function on serum levels of osteocalcin, a vitamin K-dependent protein synthesized in bone. Cord blood osteocalcin was nearly double that of maternal osteocalcin, but there was no correlation between the two. Infants with Apgar scores less than or equal to 7 had a lower mean serum osteocalcin value (8.7 ng/ml, n = 8) than did those with scores of 8 to 10 (16.6 ng/ml, n = 38). Serum osteocalcin elevation coincided with the pubertal growth spurt. In boys, levels decreased to adult values by 18 years of age, as do other indices of bone metabolism; in girls, the levels decreased earlier and had a less pronounced maximum. In children with renal failure, osteocalcin was substantially increased, presumably because of diminished renal clearance of the protein. Children receiving peritoneal dialysis, however, had mean serum concentrations less than half of those seen in children receiving hemodialysis (117 vs 328 ng/ml). The peritoneal dialysate contained significant amounts of osteocalcin, but none was detectable in hemodialysate. Correlation between bone disease and serum osteocalcin was evident in a longitudinal study of one patient with renal failure. Children with various forms of rickets had elevated osteocalcin levels; hypoparathyroidism and osteoporosis were accompanied by variable changes. Serum osteocalcin holds promise as a useful marker of subacute changes in bone metabolism.

Increased inorganic sulfate in mother and fetus at parturition: Evidence for a fetal-to-maternal gradient

Inorganic sulfate is a cosubstrate for numerous sulfoconjugation reactions, including sulfation of estrogen steroids in the fetoplacental unit. It is known that the availability of inorganic sulfate can be the rate-limiting factor in these reactions, but fluxes of inorganic sulfate across the maternal-placental barrier have not been well characterized. Therefore, we measured serum inorganic sulfate in matched samples from 46 mothers and fetuses at parturition to identify any maternal-fetal gradient and explore clinical correlations. The concentration of inorganic sulfate, measured by controlled-flow anion chromatography, was significantly higher (p = 0.006) in fetal cord blood [458 +/- 10 microM; mean +/- SE] than in the maternal circulation [431 +/- 19 microM]. That a gradient was not observed for chloride ion rules out sampling artifact as a source of the difference. Maternal and fetal concentrations of inorganic sulfate were highly correlated (r = 0.84, p less than 0.001). No influence was observed for gestational history, newborn weight, sex, or Apgar scores, but values were significantly higher in those with relatively shorter (less than 36 weeks) or longer (greater than 41 weeks) gestations. We demonstrated that a small but significant fetal-to-maternal inorganic sulfate gradient exists at birth, but the origin of this gradient is not known.

Sulfate transport in brush border membrane vesicles prepared from human placental syncytiotrophoblast

Isolated brush-border membrane vesicles prepared from human placenta are known to transport amino acids via a Na+-dependent mechanism akin to that found in gut and kidney vesicle preparations. We studied sulfate transport in placental vesicles and failed to identify any Na+-dependent uptake mechanism. Rather, uptake is a non-electrogenic process that is trans-stimulated by outwardly directed anion flux which is independent of cation. If anion exchange is tightly coupled in vivo, the net transfer of sulfate from mother to the growing fetus may be driven by the continuous flux of bicarbonate in the opposite direction.

Pitfalls in the initial diagnosis of tyrosinemia: Three case reports and a review of the literature

The tyrosinemias are a complex and heterogeneous group of disorders in tyrosine catabolism that embrace a wide spectrum of clinical conditions, ranging from the benign neonatal variety to the severe hepatorenal form. Readily available diagnostic tests are too insensitive to distinguish between these variants, and more definitive but technically difficult tests can be performed rapidly in only a few centres. Effective management may therefore be compromised, due to the inability of obtaining a working diagnosis quickly. This report describes difficulties encountered with conventional testing in three patients. Analysis of whole blood delta-aminolevulinic acid dehydratase activity and determination of urinary inhibition activity against the enzyme were found to be rapid and reliable screening tests for hepatorenal or type I hereditary tyrosinemia. These procedures are recommended in the initial evaluation of undifferentiated tyrosinemic states.

Changes in serum osteocalcin associated with parathyroid hormone infusion in X-linked hypophosphatemic rickets

Osteocalcin is a protein unique to bone that can be quantitated in serum by radioimmunoassay. While its function remains unknown, it appears to be a sensitive marker of changes in bone activity. To determine its relationship to parathyroid hormone action, we measured serum osteocalcin in blood samples obtained from patients with vitamin D-resistant rickets before and after administration of exogenous parathyroid hormone. Serum osteocalcin was decreased by 35% at 15 min after infusion and gradually returned toward normal levels by 75 min. We suggest that the acute decline in serum concentrations after infusion is an indication of inhibition of osteoblast activity. Thus, osteocalcin may be a useful means of assessing bone responsiveness to parathyroid hormone.

Determination of inorganic sulfate in human saliva and sweat by controlled-flow anion chromatography: Normal values in adult humans

Following the previous demonstration that low concentrations of inorganic sulfate (SO4) in human serum and cerebrospinal fluid can be accurately determined by controlled-flow anion chromatography, the assay has been extended to the quantitation of free SO4 in saliva and sweat by modification of the established methods of sample collection and preparation. Salivary secretions were ultrafiltered to remove macromolecular polyanions that bind irreversibly to the anion-exchange separator column and reduce resolution. Sweat was collected from 22 fasted adult volunteers using a method which utilizes absorbent filter pads applied to the forearm after secretion had been stimulated by pilocarpine iontophoresis. It was necessary to acid wash the filter pads to reduce sulfate contamination. Saliva ultrafiltrate or sweat was diluted and injected onto a Dionex D-10 Ion Analyzer using the standard anion column system. The mean inorganic SO4 concentration in saliva from seventeen adult fasting volunteers was 72 +/- 4 mumol/l (+/- S.E.); the mean SO4 concentration in sweat was 83 +/- 3 mumol/l. Both are significantly less than in matching serum, suggesting that SO4 is actively removed during formation of these glandular secretions. The ion chromatographic assay is shown to be capable of measuring SO4 in biological fluids at concentrations that are otherwise undetectable by conventional assay techniques.

Clearance of Inorganic Sulfate by Peritoneal Dialysis in Children with Chronic Renal Failure

The peritoneal clearance of inorganic sulfate was measured in 6 infants and 12 children with end-stage renal disease who were receiving continuous ambulatory peritoneal dialysis. Serum sulfate, which was elevated before dialysis, changed little during the 5-hour dialysis period. The dialysis sulfate concentration increased at the same rate as creatinine. Net clearance of the two metabolites was not different. It was calculated that the removal by continuous ambulatory peritoneal dialysis in 24 h is comparable to the daily excretion of SO4 in healthy children.

The Hypocalcemic Effect of Inorganic Sulfate Infusions

Inorganic sulfate is a divalent anion that forms a soluble ion-pair complex with serum calcium, but the extent to which infusions of sulfate salts may depress the concentration of ionized calcium has never been quantitated. In a study of 9 patients who received sodium sulfate infusions as part of a standard diagnostic workup for their renal tubular acidosis, we observed a decrease in mean ionized calcium (adjusted to pH 7.40) from 1.15 +/- 0.01 to 1.04 +/- 0.02 mmol/l (p less than 0.01). The changes in ionized calcium were highly correlated with those in serum sulfate (r2 = 0.95; p less than 0.01). Quantitatively, an increase of 1 mmol/l in serum sulfate was associated with a decrease of 0.017 mmol/l in ionized calcium, a result that is in close agreement with in vitro data based on simple salt solutions. Diagnostic sulfate infusions should be used with caution in any patient predisposed to hypocalcemia.

Inorganic Sulfate Metabolism in the Very Low Birthweight Infant

The effect of vitamin D supplementation on inorganic sulfate metabolism was examined in very low birth weight (less than 1,500 g) infants at biweekly intervals after birth until 6 weeks of postnatal age. Baseline serum sulfate concentrations were significantly higher in all infants (471 +/- 24 mumol/l, n = 80) than in adults (299 +/- 25 mumol/l, n = 17). In controls, the levels did not change significantly over the ensuing 6 weeks, although serum creatinine declined. Urinary sulfate excretion rose significantly to near adult levels by 2 weeks. Both urine and serum sulfate were correlated with weight gain but not with estimated glomerular filtration rate, suggesting that factors other than renal clearance have a preponderant influence on serum sulfate in these infants. At 6 weeks, the mean serum sulfate in the high-dose group (receiving 2,170 +/- 23 U/day of vitamin D, n = 41) was significantly higher than in controls (receiving 360 +/- 22 U/day, n = 40). In all infants, there was a significant correlation (r = 0.36, p less than 0.001) between serum sulfate and 25(OH)-vitamin D concentrations, but not other analytes or clinical variables, suggesting that vitamin D may be one of the factors modulating sulfate metabolism in the newborn period.

Ethanolaminuria: A non-specific laboratory finding in the seriously III infant

Ethanolamine is a compound that is frequently seen in urinary amino acid analysis. Although there is a single report of increased ethanolamine excretion associated with a distinctive storage disease in two siblings, the significance of ethanolaminuria is not known. We measured urinary ethanolamine/creatinine ratios in 102 hospitalized infants under two years of age and examined the clinical correlations in six cases whose ratios were more than five-fold higher than the maximum value for the established reference range. We found that ethanolamine excretion was strongly dependent on age even when the data were corrected for significant positive skewing. Increased ethanolamine excretion was common in the first week of life, but five of the six cases we specifically studied were characterized by progressive, debilitating illness and three of the six patients subsequently died. Although we found no evidence of a storage disorder, we did note that there was evidence of neuronal white matter degeneration in most but not all cases. Thus, ethanolaminuria appears to be a non-specific sign of severe neurological disease rather than a distinctive feature of a specific inborn error of metabolism.