Spurious Elevation of Multiple Urine Amino Acids by Ion-Exchange Chromatography in Patients with Prolidase Deficiency

Abstract

The enzyme prolidase cleaves dipeptides where the C-terminal amino acid corresponds to proline or hydroxyproline. As a consequence, a deficiency of this enzyme leads to accumulation of these dipeptides, which correspondingly are found to be elevated in urine. In fact, the absence of dipeptiduria is sufficient to rule out a diagnosis of prolidase deficiency. However, given the fact that these dipeptides elute at the same position as more common amino acids, the analyzer’s software will instead call an elevation of these corresponding amino acids. Thus, an elevation of glycylproline, aspartylproline, glutamylproline, threonylproline and serylproline, valylproline, leucylproline, isoleucylproline, alanylproline, phenylalanylproline, and lysylproline will instead be interpreted as an elevation of leucine, citrulline, methionine, isoleucine, beta-aminoisobutyric acid, gamma-aminobutyric acid, ethanolamine, tyrosine, histidine, and anserine/carnosine, respectively. This particular profile of elevated amino acids, however, can easily be overlooked. We hope that the recognition of this characteristic pattern of falsely elevated urinary amino acids will aid in the recognition of prolidase deficiency.

Competing interests: None declared

A Concise One Sentence Take-Home Message

Prolidase deficiency can lead to a particular pattern of spurious elevation of several urine amino acids, given their coelution with uncleaved imidodipeptides.

Compliance with Ethics Guidelines

Conflict of Interest

• Carlos R. Ferreira and Kristina Cusmano-Ozog declare that they have no conflict of interest.

• No identifying information about patients is included in the article.

• This article does not contain any studies with animal subjects performed by the any of the authors.

• Writing, preparation, and critical review of the manuscript: CRF and KCO.