Fabry disease is a rare genetic disease that can affect many organs, including the kidneys. The disease is caused by mutations in the GLA gene that provides instructions for producing an enzyme called alpha-galactosidase A. This enzyme is required for breaking down a fat molecule called globotriaosylceramide (Gb3 or GL3); when it does not function properly Gb3 accumulates inside cells, causing damage and leading to the symptoms of Fabry disease.
Urine tests, or urinalysis, is a non-invasive and cost-effective tool for diagnosing different pathological aspects of Fabry disease, as well as monitoring disease progression and treatment effectiveness.
How urine tests work
Urine is produced by the kidneys, which filter waste from the blood and help regulate water and electrolyte levels in the body. Changes in urine color and content are useful in diagnosing underlying medical issues, including Fabry disease.
Many features of urine can be analyzed:
- its color and clarity;
- its chemical composition that can help identify changes in the concentration of various components such as sugar, proteins, bilirubin, creatinine, and Gb3;
- its microscopic structure to identify and count the presence of cells.
Urine tests and Fabry disease
Different urine tests can be used for diagnosing Fabry disease. These are summarized below.
Analysis of the levels of Gb3
In Fabry disease, the levels of Gb3 are significantly higher inside cells and in the blood and urine. In general, the electrospray ionization mass spectrometry (ESI-MS) technique is used to analyze the concentrations of different isoforms of Gb3, namely, Gb3-24 and Gb3-18. A higher-than-normal total urinary Gb3 concentration and a ratio of Gb3-24 to Gb3-18 that is greater than 2.3 are indicative of Fabry disease.
Urinary protein and albumin levels
Proteinuria (protein in urine) and albuminuria (albumin in urine) occur when large numbers of kidney cells die, are broken down, and the contents leak into urine. So, they also are indicative of kidney disease that may be caused by Fabry disease.
The levels of a protein called bikunin are elevated in the urine of patients with acute kidney disease. So, urine bikunin levels can be used to monitor kidney function in Fabry disease patients.
Research has shown that urinary mulberry cells are a useful marker for Fabry disease, including renal-variants of Fabry disease. Mulberry cells are kidney-derived cells with accumulated Gb3. These cells can be identified by an expert pathologist upon the microscopic examination of the urine.
Urine-derived cell cultures
Research has shown that urine-derived cells can be cultured in the laboratory and used to detect the enzymatic activity of alpha-galactosidase A. These cells also can be used for genetic testing to determine the types of mutations that cause Fabry disease.
Last updated: Oct. 10, 2019
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