Measuring glucocerebrosidase (GCase) activity in dried blood spots is a reliable and cost-effective method to diagnose Gaucher disease early in individuals with splenomegaly (enlarged spleen) and/or thrombocytopenia (low blood platelet count), a study has found.
The study, “High risk screening for Gaucher disease in patients with splenomegaly and/or thrombocytopenia in China: 55 cases identified,” was published in the journal Clinical Chimica Acta.
Gaucher disease (GD) is caused by mutations in the GBA gene, which results in insufficient levels of the GCase enzyme and accumulation of a fat molecule called glucosylceramide in macrophages — then called Gaucher cells.
Several biomarkers are widely used in assisting the diagnosis of GD and monitoring treatment efficacy. One such biomarker is chitotriosidase, an enzyme produced by Gaucher cells.
However, given GD’s non-specific and variable symptoms, many patients may be misdiagnosed or remain undiagnosed for years.
Recently, a GCase assay in dried blood spots (DBS) has been used in GD screening. DBS is a form of sampling where blood samples are blotted and dried on filter paper. These dried samples can then be shipped to a laboratory to be analyzed.
In the study, a group of Chinese researchers set out to evaluate a screening program for patients at high risk for GD by measuring the enzyme activities of GCase and chitotriosidase in DBS. All participants had unexplained splenomegaly and/or thrombocytopenia.
Patients with GCase activity under 3.0 picomol (pmol)/punch/h were screened as positive. GD diagnosis was then confirmed by sequencing the GBA gene.
The study enrolled 787 high-risk patients (364 females and 423 males) from May 2016 to August 2019.
Results showed that 131 (16.6%) participants screened positive, 79 had GCase activity just above the cut-off (up to 4 pmol/punch/h), and 577 had normal GCase levels.
Among the positive cases, 49 patients had confirmed GD through GBA sequencing. This led to a positive predictive value — the probability that patients with a positive screening test have the disease — of 37.4%.
Three patients with GCase activity just above the threshold and another three with normal GCase activity whose spleen had been removed were suspected of having GD due to increased chitotriosidase or Gaucher cells in the bone marrow. All six patients were confirmed to have GD by GBA genetic analysis. As a result, 55 GD cases were identified in total.
The sensitivity (true positives) of the screening was 98.2%, and its specificity (true negatives) was 89.5%.
All 55 GD patients had splenomegaly, 69.1% had hepatomegaly (enlarged liver), and 83.6% had thrombocytopenia with or without anemia. Their median age at diagnosis was 14 years (age range was from 1 month to 59 years).
The average GCase activity of GD patients was 1.7 pmol/punch/h. Levels of chitotriosidase were higher than normal in 42 GD patients but were undetectable in the other 13.
Genetic analysis identified 44 mutations in the GBA gene, including 11 novel mutations. The most common variant is known as c.1448T>C (p.L483P) — an amino acid change from leucine to proline at position 483, which was found in 30.8% of patients.
Overall, “our data demonstrated that the high risk screening program for GD by measurement of GCase and chitotriosidase in DBS is a reliable and cost-effective method for early diagnosis of GD in patients with unexplained splenomegaly and/or thrombocytopenia in China,” the scientists wrote.
However, the relatively high frequency of undetected chitotriosidase in the study population suggests the need to search for an alternative biomarker, they added.
