Laboratory LC-MS/MS algorithm for detecting primary creatine disorders.

Background:

Primary creatine disorders (PCDs) are a group of diseases caused by defects in biosynthesis or transport of creatine. That involves arginine:glycine amidinotransferase (AGAT) deficiency (OMIM 602360), guanidinoacetate methyltransferase (GAMT) deficiency (OMIM 601240) and defect of the creatine transporter (SLC6A8, OMIM 300036) resulting in characteristic biochemical finding.

Methods:

We have developed tandem mass spectrometry (MS/MS) based methodical approach for quantification of gunidinoacetate (GAA), creatine (CR) and creatinine (CRN) in urine, serum/plasma and dried blood spot (DBS) samples in order to reveal PCDs in clinical practice.

Results:

First urinary screening step covering investigation of almost all patient employs 3 minutes flow injection analysis (FIA)-MS/MS method for quantification of GAA, CR and CRN requiring just 5 µL of urine or one DBS punch sample. In case of low/high GAA or CR excretion, second-tier column LC-MS/MS method is applied to confirm findings in urine and serum/plasma sample subsequently. We have defined a reference range for GAA and CR in urine, serum/plasma and DBS based on the age. So far, we have detected one patient with GAMT deficiency (high GAA in U/S,P/DBS) and two patients with SLC6A defect (high CR U).

Conclusion:

Our laboratory MS/MS algorithm is a reliable and high throughput tool for PCDs diagnostics.

Minimal volume sample demand coupled with a rapid run time make the method applicable to the routine screening test. Because some unknown GAA interferences have been described the second-tier step is necessary to discriminate isobaric ions and confirm the primary screening suspicion.

Acknowledgement: Supported by MH CZ – DRO VFN64165.