Biochemical evaluations at two time points in 15 patients with nephropathic cystinosis under cysteamine treatment

Background
Nephropathic cystinosis (NC) (MIM #219800) is a rare autosomal recessive disorder that is characterized by accumulation of cystine in many tissues and organs, especially kidney and eyes. It occurs in ~1–2 of 100 000 live births. NC is caused by mutations in the gene encoding the lysosomal membrane transporter cystinosin. Cystinosin deficiency results in lysosomal cystine accumulation in different organs and systems. Cysteamine is the mainstay treatment to deplete the cystine accumulation. The aims were to establish white blood cell cystine measurement using mass spectrometry and evaluate the effect of treatment through measurement of some biochemical markers.
Patients and methods
The study included 15 patients with NC referred from the cystinosis outpatient clinic of Department of Pediatrics, Cairo University, over the period from June 2018 to January 2019 and 25 healthy normal participants as controls. Venous blood samples were taken for studying the effect of treatment through measurement of cystine level, chitotriosidase activity, thyroid profile, free carnitine, and acylcarnitine concentrations at two time points of evaluation. The basic evaluation was started in the beginning of June 2018, and the follow-up was started in the beginning of January 2019.
Results
Cystine concentration in 10 patients was decreased from the range of 4–13 to 2.3–8.5 nmol ½ cystine/mg proteins; eight patients had high activity of chitotriosidase (170–574 μmol/l/h), and then the activity range decreased to 90–371.5 μmol/l/h under treatment. One patient had high thyroid-stimulating hormone level (32 UI/ml), which was normalized to 12 UI/ml in the follow-up, and three patients had a high borderline thyroid-stimulating hormone level (20, 21, and 25.9 UI/ml) in the follow-up stage. Levels of free carnitine and acylcarnitine were normal at the two points of evaluation.
Conclusion
The current study draws attention to the importance of a follow-up policy, especially in Arabic countries, which have a high rate of consanguineous marriages.