title: The measurement of urinary Δ¹-piperideine-6-carboxylate, the alter ego of α-aminoadipic semialdehyde, in Antiquitin deficiency.
abstract: The assessment of urinary α-aminoadipic semialdehyde (α-AASA) has become the diagnostic laboratory test for pyridoxine dependent seizures (PDS). α-AASA is in spontaneous equilibrium with its cyclic form Δ(1)-piperideine-6-carboxylate (P6C); a molecule with a heterocyclic ring structure. Ongoing diagnostic screening and monitoring revealed that in some individuals with milder ALDH7A1 variants, and patients co-treated with a lysine restricted diet, α-AASA was only modestly increased. This prompted us to investigate the diagnostic power and added value of the assessment of urinary P6C compared to α-AASA. Urine samples were diluted to a creatinine content of 0.1 mmol/L, followed by the addition of 0.01 nmol [(2)H(9)]pipecolic acid as internal standard (IS) and 5 μL was injected onto a Waters C(18) T3 HPLC column. Chromatography was performed using water/methanol 97/3 (v/v) including 0.03 % formic acid by volume with a flow rate of 150 μL/min and detection was accomplished in the multiple reaction monitoring mode: P6C m/z 128.1 > 82.1; [(2)H(9)]pipecolic acid m/z 139.1 > 93.1. Due to the dualistic nature of α-AASA/P6C, and the lack of a proper internal standard, the method is semi quantitative. The intra-assay CVs (n = 10) for two urine samples of proven PDS patients with only modest P6C increases were 4.7% and 8.1%, whereas their inter-assay CVs (n = 10) were 16 and 18% respectively. In all 40 urine samples from 35 individuals with proven PDS, we detected increased levels of P6C. Therefore, we conclude that the diagnostic power of the assessments of urinary P6C and α-AASA is comparable.
authors.affiliation: Metabolic Unit, Department of Clinical Chemistry, VU University Medical Center Amsterdam, Amsterdam, The Netherlands. e.struys@vumc.nl
authors.forename: Eduard A
authors.initials: EA
authors.lastname: Struys
authors.forename: Levinus A
authors.initials: LA
authors.lastname: Bok
authors.forename: Dina
authors.initials: D
authors.lastname: Emal
authors.forename: Saskia
authors.initials: S
authors.lastname: Houterman
authors.forename: Michel A
authors.initials: MA
authors.lastname: Willemsen
authors.forename: Cornelis
authors.initials: C
authors.lastname: Jakobs
mesh_terms: D015074:2-Aminoadipic Acid / Q000031:analogs & derivatives* / Q000652:urine; D000444:Aldehyde Dehydrogenase / Q000172:deficiency* / Q000235:genetics; D004032:Diet; D004827:Epilepsy / Q000175:diagnosis* / Q000235:genetics / Q000378:metabolism / Q000652:urine*; D006801:Humans; D008239:Lysine / Q000378:metabolism; D010848:Picolinic Acids / Q000652:urine*
chemical_list: D010848:Picolinic Acids; D015074:2-Aminoadipic Acid; C008919:delta-1-piperidine-6-carboxylic acid; C000061:allysine; C089507:ALDH7A1 protein, human; D000444:Aldehyde Dehydrogenase; D008239:Lysine