A role for magnesium in neonatal parathyroid gland function?

HYDROCEPHALY, SCHIZENCEPHALY, SPONDYLOCOSTAL DYSPLASIA, AND HYPOPARATHYROIDISM IN AN INFANT OF A DIABETIC MOTHER

CONTEXT

Diabetes mellitus is the most frequent chronic complication in pregnancy and continues to contribute to increased perinatal morbidity and mortality in newborns. Macrosomia, respiratory distress syndrome, metabolic and electrolytic disturbances, and increased rates of congenital structural defects are well-known neonatal complications associated with maternal diabetes, even if well-controlled.

CASE REPORT

A macrosomic infant born from an insulin-dependent mother, with uncontrolled diabetes and lack of adequate prenatal care, prenatally diagnosed with hydrocephaly showed a complicated postnatal course. Initial respiratory distress syndrome and transient hypoglycemia, rapidly corrected under treatment, were followed by persistent hypocalcemia and hyperphosphatemia due to hypoparathyroidism and evolving hydrocephaly. Ventriculoperitoneal shunting was followed by resolution of hypocalcemia, but seizures associated with schizencephaly and recurrent respiratory tract infections, aggravated by spondylocostal dysplasia, concurred to infant's demise at the age of 5 months.

CONCLUSIONS

The reported case is rare due to multiple aspects: persistent hypoparathyroidism, uncommon association of schizencephaly, and even rarely association with spondylocostal dysplasia, all these conditions requiring a multidisciplinary therapeutic approach. Also, the reported case is evocative for challenges associated with infants born from diabetic mothers.

Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones

Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.

Increased renal tubular reabsorption of calcium and magnesium by the offspring of diabetic rat pregnancy

Diabetic pregnancy has a marked influence on offspring calcium and magnesium homeostasis. Urinary excretion of calcium and magnesium is reduced, yet offspring of diabetic pregnancy exhibit hypomagnesemia and hypocalcemia. The aim of this study was to measure renal hemodynamic and tubular function in the offspring of diabetic (OD) and control, nondiabetic (OC) rats at 4 and 8 wk of age to determine the glomerular and tubular mechanisms through which renal calcium and magnesium handling are programmed in utero. The fraction of filtered calcium that was excreted was significantly lower in OD at both 4 and 8 wk of age [8 wk: OC (n = 6), 11.8 +/- 2.9 versus OD (n = 5), 4.3 +/- 0.6%; p < 0.05] and that of magnesium was lower at 8 wk of age [OC (n = 6), 42.4 +/- 7.5 versus OD (n = 5), 13.0 +/- 1.7%; p < 0.01]. This increased reabsorption occurred despite an elevated GFR in OD. These findings clearly indicate that tubular reabsorptive mechanisms for calcium and magnesium are increased markedly in OD. Serum PTH concentration was reduced in 8-wk-old OD [OC (n = 7), 539.4 +/- 142.1 versus OD (n = 9), 174.3 +/- 69.4 pg/ml; p < 0.05], consistent with previous reports in human infants. Taken together, these observations suggest that the basis for the altered renal magnesium and calcium handling in OD involves increased tubular transport activity and possibly increased sensitivity of these mechanisms to PTH.

Serum ionized magnesium in premature and term infants

Magnesium is the element with the second highest concentration in the body and is found almost entirely in the intracellular compartment. The small serum component gives a poor representation of the active, physiologic state of the metal. This state is assessed much better by measuring ionized magnesium in the serum, which can now be performed with a sensitive ion-selective electrode. This study was undertaken to establish the normal serum ionized magnesium levels in newborn infants and to define normal serum ionized calcium/ionized magnesium ratios. Ninety-seven infants were investigated. Six were born before 32 weeks gestation, 28 between 33 and 37 weeks gestation, and 63 were term. Ionized magnesium levels were 0.69 +/- 0.14 mmol/L, 0.63 +/- 0.10 mmol/L, and 0.57 +/- 0.07 mmol/L in each group, respectively. These findings demonstrate a significant decline in serum ionized magnesium with increasing maturity. This decrease may relate to a greater need for magnesium uptake during earlier gestation, more magnesium-induced vasodilation to maintain adequate blood flow to developing tissues and organs, or immature parathormone function earlier in pregnancy. The progressive rise in serum ionized calcium/ionized magnesium ratios found herein supports the latter hypothesis.

Whole blood ionized magnesium in the healthy neonate

OBJECTIVE

We aimed to determine the normal range of ionized magnesium (IMg2+) concentration at birth and 24 hours of life in the healthy, term (37 to 41 weeks old) neonate.

METHODS

Cord blood was obtained from the umbilical vein of 30 patients. In addition, blood was obtained from 32 infants at 24 hours of life. Whole blood was analyzed to determine IMg2+ concentration, ionized calcium concentration, and pH.

RESULTS

The normal range of IMg2+ concentration (mean +/- 2 SD) was found to be 0.40 to 0.56 mmol/L (0.97 to 1.36 mg/dL) at both birth and 24 hours of life.

CONCLUSIONS

The normal range of IMg2+ concentration (mean +/- 2 SD) in the healthy neonate at birth and 24 hours of life is 0.40 to 0.56 mmol/L (0.97 to 1.36 mg/dL). This range can serve as a reference value for future studies regarding the clinical usefulness of IMg2+ concentration determination in neonatal disease states.

Neonatal hypocalcemia: to treat or not to treat? (A review)

The various definitions of neonatal hypocalcemia (NHC) are critically examined. The authors review the known and less known complications of NHC and of its treatment. They emphasize the need for a definition of NHC in terms of serum ionized rather than total calcium concentrations, the rationale for treating symptomatic NHC, as well as the need for further research in infants with asymptomatic NHC.

New whole blood analyzers and their impact on cardiac and critical care

Miniaturized whole blood biosensors, patient-focused hospitals, and rising expectations of patients and physicians are shifting laboratory diagnostics to the point of care. Expanding transplantation and intensive care are increasing the need for rapid test results. Whole blood analysis improves accuracy, eliminates centrifugation, reduces response time, and conserves blood volume. Several hand-held, and over 20 portable or transportable whole blood instruments are now available. Criteria for instrument evaluation include test menus, point-of-care features, analysis time, on-site performance, and information integration. Whole blood analyzers measure several vital indicators (pO2, pCO2, pH, hematocrit, K+, Ca2+, Na+, Cl-, glucose, and lactate) simultaneously in less than 2 min with less than 200 microliters of whole blood. Other in vitro tests are available (Mg2+, osmolality, CO2 content, urea nitrogen, beta-hydroxybutyrate, hemoglobin, coagulation) or under development (HCO3- phosphorus). Some can be monitored in vivo (O2 saturation, pO2, pCO2, pH, glucose) or ex vivo. The clinical impact is demonstrated by ionized calcium, now established in importance for cardiac and neurologic problems, and ionized magnesium, a promising new measurement. The hybrid laboratory (a composite of conventional clinical laboratory and patient-focused testing), performance maps, and quality paths facilitate implementation of new whole blood analyzers for optimal support of cardiac and critical care, and improved patient outcomes (prospects).