Second-tier test for quantification of alloisoleucine
and branched-chain amino acids in dried blood spots to improve newborn screening for maple syrup urine disease (MSUD).
Leucine, isoleucine, alloisoleucine
, and hydroxyproline all have molecular weights of about 131 and are quantitated together for this reason.
The metabolic profile may be further complicated by intermediate metabolites such as 3-and 4-hydroxyisovaleric acid (5), methylsuccinic acid (6), methylfumaric acid (7), isovalerylglucuronide (8), isovalerylglutamic acid (9), N-isovalerylalanine and N-isovalerylsarcosine (10), isovalerylcamitine (11), 3-hydroxyisoheptanioc acid (12), and alloisoleucine
Plasma alloisoleucine was slightly increased in patient 1 (although this was against a background of slight increases in other branched-chain amino acids) and within the reference interval in patient 2.
Plasma alloisoleucine, the first intermediate of the Rpathway, was also slightly increased in one patient, but this was an inconsistent finding because the concentration was within the reference interval in another patient.
Initial catabolic steps of isoleucine, the R-pathway and the origin of alloisoleucine.
15N conservation in the metabolic conversion of isoleucine to alloisoleucine in the rat.
We therefore examined the (patho)physiological significance of alloisoleucine plasma concentrations for the differential diagnosis of MSUD.
The range for reliable quantification of alloisoleucine was 0.
Sensitivity estimates were based on the relationship between the number of plasma samples with alloisoleucine concentrations beyond the cutoff value and the total number of plasma analyses.
To establish alloisoleucine reference values, plasma branched-chain amino acids were measured in healthy subjects, children (3-10 years), and infants (<3 years).
To assess the effect of dietary isoleucine on plasma alloisoleucine concentrations, loading tests were performed.