Pipecolic acid levels in serum and urine from neonates and normal infants: comparison with values reported in Zellweger syndrome.

Pipecolic acid (PA) excretion from normal newborn, preterm and/or small-for-dates infants has been determined and correlated with gestational age, sex and age after birth. An effect of fetal sex was not detectable. Only small-for-dates infants with a gestational age of greater than 34-37 weeks had a lower urinary excretion of PA than the appropriate-for-dates infants with the same gestational age. Preterm infants had a higher excretion of PA than term neonates. PA excretion of infants decreases with age after birth. This higher excretion in "younger" infants can be explained by a higher serum concentration and less efficient tubular reabsorption. PA level in serum and urine remains a valuable tool for the confirmation of the clinical diagnosis of Zellweger syndrome when gestational age and age after birth are taken into consideration. No PA was detected in serum or urine of four children suffering from hyperthyroidism.