[Abnormal lipoprotein (LP-X) in the first months of life with particular reference to obstructive jaundice (author's transl)].

Abnormal lipoprotein (LP-X) represents a specific parameter for the presence of obstructive jaundice in the adult. Since LP-X has also been detected in the serum of newborn infants, both full-term and premature, and in early infancy, in the absence of clinical evidence of obstructive jaundice, extensive investigations were undertaken in infants during the neonatal period to clarify this phenomenon. The present study reports the data obtained in over 2000 sera from over 370 infants (mature newborn and premature newborn and young infants), tested more or less continuously by means of the Rapidophor method, initially on a qualitative, and subsequently, on a semi-quantitative basis. LP-X appears within the first fortnight in newborn infants, irrespective of the mode of feeding. The LP-X concentration was correlated to the birth weight. Premature infants displaying signs of immaturity possessed markedly higher LP-X levels than mature newborn infants. LP-X was not correlated to the alkaline phosphatase level, nor to the gammaglutamyl transferase activity; the bilirubin level, likewise, had no connection with the LP-X concentration. Patients with proven obstructive jaundice showed distinctly higher LP-X concentrations (greater than 56 mg/100 ml), whereby the rise in LP-X level in some cases preceded the appearance of the clinical manifestations of obstructive jaundice. The following hypotheses are advanced in order to explain the presence of LP-X during the neonatal period and are discussed on the basis of clinical observations in adults, the physiological conditions in the newborn infant and the results of the present study: The liver, which occupies the central position amongst metabolic organs, also in the case of the lipoproteins, is at a physiological stage of organic and functional maturation during this early period of life. Under these circumstances, a pseudo-obstructive mechanism on the basis of insufficient excretion of biliary lipoproteins, in conjunction with a simultaneous "physiological" deficiency of lecithin: cholesterol acyl transferase could lead to the appearance of LP-X in the serum. Catabolism of the resultant LP-X cannot take place owing to an inadequate activity of lipoprotein lipase. Functional immaturity can be presumed in the case of both enzyme systems during the neonatal period. On attainment of a degree of maturity compatible with the appropriate neonatal stage, the LP-X values become negative between the 7th and the 16th week of life. It is conceivable that the appearance of LP-X in the newborn infant can be ascribed to LP-X1, since the "physiological" LP-X concentrations in the neonatal period (values of up to 20 mg/100 ml) are distinctly lower than the values found in obstructive jaundice. LP-X determination can be rated as a useful supplementary investigation in the differential diagnosis of extrahepatic biliary atresia during the first weeks or months of life...