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A study of 64 infants from one to six months of age was made using the 32-hour parenteral magnesium load test. Most of the infants were studied for neuromuscular hyperirritability or other signs compatible with magnesium deficiency; some with unrelated problems served as controls. Magnesium retention below 40 per cent was found in 26 infants who presented with minor signs or signs that were otherwise explained, as by infection. Twelve who retained 72 per cent of the load were normal or small at birth, amply fed on demand, and grew at accelerated rates, increasing from the 50th to the 88th mean percentile by ten weeks, when they were "fat, hungry, jumpy babies," exemplifying the Mg deficiency syndrome of growth. Seven infants of 8.2 ± 1 weeks had had one or more sudden, transient episodes that included: apnea, gasping, tonic or tonic-clonic fits, and flaccidity, often with pallor, cyanosis, eye signs, sweating, or tearing. Despite preload Mg in two, the group retained 88 per cent of the toad. Mg appeared to be specific therapy in high retention groups. The signs are nonspecific but resemble premonitory signs and the type of episode that may occur in the sudden infant death syndrome (SIDS), suggesting a possible link between magnesium depletion and SIDS. [ABSTRACT FROM AUTHOR]

Parenteral magnesium load tests were conducted on 91 infants less than one month of age, most of whom had marked hyperirritability arid symptoms compatible with the diagnosis of electrolyte imbalance with relative or absolute magnesium deficiency. Most of the patients studied had a 40-hour test, with an eight-hour preload and a 32-hour postload collection of urine. Of 43 premature infants studied, only three retained less than 40 per cent of the load: one was untreated, one had low retention of a second load following a course of therapy, and the mother of the third had received magnesium within 24 hours of delivery. Of 48 full-term infants studied, ten retained less than 40 per cent of the load. These were asymptornatic or had minor problems. Irritability was common in both high and low retention groups. Ten per cent of the low retention group and 50 per rent of the high retention group manifested two or more of the nonspecific signs compatible with the diagnosis of magnesium deficiency; the difference was significant (P <.025). Eleven premature and six full-term infants with very high initial retention received five or six intramuscular injections of magnesium after which the magnesium retention was about 30 per cent lower than the initial value, For most patients, repletion therapy was given orally. Although low plasma magnesium values related to high magnesium retention, correlation on an individual basis was poor. The plasma calcium levels of three patients with combined hypomagnesmia and hypocalcemia failed to respond to calcium therapy and remained low until the plasma magnesium value was corrected. Magnesium appeared to be specific therapy for symptomatic infants found to be deficient. More males than females had sufficient symptoms to warrant study. [ABSTRACT FROM AUTHOR]