title: Quantification of N-acetylaspartic acid in urine by LC-MS/MS for the diagnosis of Canavan disease.
abstract: Canavan disease is an autosomal recessive leukodystrophy characterized by excessive excretion of N-acetylaspartic acid (NAA) in urine. The disease is caused by deficiency of aspartoacylase, the enzyme responsible for the hydrolysis of NAA into acetate and l-aspartate. Patients, who are often asymptomatic in their early months, show a wide spectrum of clinical presentation thereafter that includes macrocephaly, poor head control, seizures, abnormal muscle tone, optic atrophy, significant developmental delay and death. In this work, we describe a simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of NAA in urine. The internal standard d3-NAA was added to untreated urine and the mixture was injected into the LC-MS/MS system operated in the negative ion mode. Detection was achieved in multiple reaction monitoring (MRM) mode by monitoring m/z 174 --> 88, 174 --> 130 and 174 --> 58 for NAA and 177 --> 89 for the internal standard. Separation was carried out on a C8 column (2.1 x 150 mm) using a mixture of acetonitrile and water (1:1 v/v) containing 0.05% formic acid at a flow rate of 0.25 ml/min. NAA was eluted at 1.6 min and the run time was approximately 2 min. Using spiked urine, the assay was linear up to 2 mmol/L with limit of quantification at 1 micromol/L (S/N = 12). NAA in patients' urine (n = 17) ranged between 366 and 21,235 mmol/mol creatinine compared to controls of <39 mmol/mol creatinine (n = 159). This LC-MS/MS method for NAA as described involved no extraction and no derivatization, showed no interference, and gave excellent recovery with low variability and short analytical time.
authors.affiliation: National Laboratory for Newborn Screening, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia.
authors.forename: O Y
authors.initials: OY
authors.lastname: Al-Dirbashi
authors.forename: M S
authors.initials: MS
authors.lastname: Rashed
authors.forename: K
authors.initials: K
authors.lastname: Al-Qahtani
authors.forename: M A
authors.initials: MA
authors.lastname: Al-Mokhadab
authors.forename: W
authors.initials: W
authors.lastname: Kurdi
authors.forename: M A A
authors.initials: MA
authors.lastname: Al-Sayed
mesh_terms: D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000652:urine; D017825:Canavan Disease / Q000097:blood* / Q000175:diagnosis*; D002648:Child; D002675:Child, Preschool; D002853:Chromatography, Liquid / Q000379:methods*; D005260:Female; D006801:Humans; D006868:Hydrolysis; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D013058:Mass Spectrometry / Q000379:methods*; D008956:Models, Chemical; D012016:Reference Values; D016482:Urinalysis / Q000379:methods*
chemical_list: D001224:Aspartic Acid; C000179:N-acetylaspartate