Normal serum creatinine (Scr) and creatinine clearance (Ccr) values during the first 10 days of life were obtained in 63 very premature (28-32 weeks of gestation), premature (33-37 weeks) and term infants (38-42 weeks). Scr fell, and Ccr rose less markedly in the very premature infants. Scr was 80 mumol/l on the 1st day of life both in very premature and premature infants, and 77 mumol/l in full-term neonates. After 10 days, Scr was 73, 53 and 35 mumol/l respectively. There was an exponential correlation between Ccr and gestational age, indicating rapid maturation of glomerular function.
A second patient with N-acetylglutamate synthetase deficiency is described. The first symptoms were noted at 6 days of age. The course was lethal despite vigorous treatment. The diagnosis was established after death.
Protein content and protein composition were studied in amniotic fluid obtained from 171 healthy pregnant women between the 16th and 38th week of gestation, using microgradient gel electrophoresis to separate proteins according to their molecular size into albumin (68 KD), proteins of low molecular weight (LMW proteins, less than 68 KD), and proteins of high molecular weight (HMW proteins, greater than 68 KD). Additionally alpha-1-microglobulin (alpha-1-MG, 33 KD) and beta-2-microglobulin (beta-2-MG, 11,8 KD) were analysed as micromolecular marker proteins. Concentrations of LMW proteins were 0.15-0.22 g/l, of alpha-1-MG 28.4-34.5 mg/l, and of beta-2-MG 7.2-11.6 mg/l during the second trimester of gestation, and thereafter decreased progressively to 0.03 g/l, 14.1 mg/l and 2.4 mg/l respectively near term. The same developmental trends were confirmed by calculating the protein/creatinine ratios in amniotic fluid. The concentrations of LMW proteins found in the first postnatal urine of 73 healthy infants born prematurely or at term were similar to those in amniotic fluid of corresponding fetal age. Concentrations of albumin and HMW proteins in postnatal urine were about 5% and 15% respectively when compared with amniotic fluid concentrations. No strong correlation existed between gestational age and either of the analysed proteins which would allow accurate assessment of fetal maturation by protein analysis in amniotic fluid. It is concluded that fetal urinary excretion is the major determinant of the microprotein content of amniotic fluid. Microproteins seem to reflect an increasing tubular reabsorption capacity, which accelerates rapidly after the second trimester of gestation.
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