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Kidney Week

Abstract: TH-PO719

Diagnosis of Adenine Phosphoribosyltransferase Deficiency by ATR-FTIR Spectroscopy

Session Information

Category: Genetic Diseases of the Kidney

  • 1002 Genetic Diseases of the Kidney: Non-Cystic

Authors

  • Lin, Tzu-Ling, University College London, London, United Kingdom
  • Unwin, Robert J., University College London, London, United Kingdom
  • Norman, Jill T., University College London, London, United Kingdom
  • Edvardsson, Vidar O., Landspital - The National University Hospital of Iceland, Reykjavik, Iceland
  • Palsson, Runolfur, Landspitali - The National University Hospital of Iceland, Reykjavik, Iceland
  • Rich, Peter R., University College London, London, United Kingdom
Background

Adenine phosphoribosyltransferase deficiency (APRTd) is a rare inherited disorder of purine metabolism characterized by renal excretion of large amounts of crystalline 2,8 dihydroxyadenine (DHA). Affected individuals develop kidney stones and progressive CKD, and eventual ESRD, secondary to renal parenchymal DHA crystal deposition; diagnosis is often missed and its true prevalence is uncertain. Currently, the primary method leading to diagnosis is the detection of DHA crystals by urine microscopy; however, several urinary crystalline species can easily be confused with DHA. Therefore, it is crucial to develop a rapid and sensitive point-of-care method for identification of DHA in human urine samples.

Methods

Fourier-transform infrared (FTIR) spectroscopy has been shown to be a straightforward and reliable technique for the diagnosis of a variety of kidney stones. We assessed attenuated total reflection (ATR) FTIR spectroscopy as a means of detecting DHA in urine.

Results

An optimal method for accurate detection and quantitation of DHA in a dried urine pellet was developed. Urine samples from untreated APRTd patients in whom the presence of DHA had been confirmed by ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS-MS) were assessed using ATR-FTIR. Insoluble DHA was detected in 17 of the 20 urine samples with concentrations ranging from 1.4 - 24.8 µM. In 3 samples, ATR-FTIR indicated the presence of a different insoluble component related to a form of uric acid or its salts, possibly in combination with other compounds. Hence, this method may be useful in routine clinical screening to identify cases of APRTd. In addition, IR analysis of pure DHA revealed a second physical form of DHA, probably an amorphous state, which has not been reported before. It is unclear whether amorphous DHA may be involved in disease pathogenesis and/or if the lack of recognition of amorphous DHA contributes to under-diagnosis of APRTd.

Conclusion

In conclusion, ATR-FTIR may be a useful and rapid ‘point-of-care’ screening tool for early diagnosis of APRTd. Both the method and instrumentation can be adapted easily and cheaply for clinical use. The clinical significance of the newly identified amorphous DHA remains to be established.

Funding

  • Private Foundation Support