Why test for glucocerebrosidase enzyme activity?

Gaucher disease is an autosomal recessive disorder secondary to mutations in the gene that encodes for the enzyme glucocerebrosidase (GBA1).1,2 Therefore, a diagnosis of Gaucher disease is often based on clinical history, physical examination and laboratory testing, and confirmed by the finding of a deficiency in the enzyme activity of glucocerebrosidase.1 Genetic mutation studies are also recommended, and a family history of the disease can support the diagnosis of suspected or proven Gaucher disease.1

Previously, a diagnosis of Gaucher disease was often made by the presence of Gaucher cells in a bone marrow aspirate or when a patient presented with an unexplained massive splenomegaly and was treated with splenectomy. However, these diagnostic methods were not accurate because many storage cells, so-called pseudo-Gaucher cells, may be confused with Gaucher cells on the marrow examination. Nevertheless, a bone marrow examination may still be needed in patients where the splenomegaly does not regress on treatment, or if the patient develops enlarged lymph nodes or B symptoms that suggest development of a lymphoma.1

What is the glucocerebrosidase enzyme activity test?

Measurement of glucocerebrosidase enzyme activity in leukocytes or skin fibroblasts on a skin biopsy is considered the ‘gold standard’ for diagnosing Gaucher disease.1,3 Dried blood spots are used as a screening assay for glucocerebrosidase enzyme activity.4 A test using approximately 5 mL of EDTA or heparinised blood is all that is necessary to confirm a diagnosis of Gaucher disease as this allows direct measurement of glucocerebrosidase activity in leukocytes.5,6 If patients have leukopaenia, cultivated skin fibroblasts from a skin biopsy can be assayed instead.5 The determination of Gaucher disease must be made by specialised laboratories with particular experience in the measurement of glucocerebrosidase activity and its interpretation.5-9 In patients with Gaucher disease, glucocerebrosidase activity levels are approximately 10‒30% of normal.8,9

Residual glucocerebrosidase enzyme activity has been shown to significantly correlate with age, chitotriosidase enzyme activity, spleen size and greater disease severity in patients with Gaucher disease.10 Yet, measuring glucocerebrosidase enzyme activity does not distinguish between patients with Gaucher disease who are heterozygote carriers of mutations in the GBA1 gene and individuals who do not have Gaucher disease. Moreover, this diagnostic blood test does not provide histological information on the bone, liver or spleen for diagnosis.1 However, a statistically significant relationship between the residual enzyme activity of glucocerebrosidase and bone involvement has been previously noted.10

Clinical experience in diagnosing Gaucher disease

Results were reported from the biochemical diagnosis of blood samples taken from 5128 patients with suspected Gaucher disease from the Biochemical Genetics laboratory in Egypt. For each patient, 5 mL of whole blood were collected by venous puncture into EDTA tubes. Plasma was obtained for chitotriosidase assay and leukocytes were separated to determine the activity of glucocerebrosidase using synthetic substrate. In all cases, measurement of glucocerebrosidase activity was conducted in parallel with the assessment of chitotriosidase in peripheral leukocytes. In healthy unaffected individuals without Gaucher disease, normal enzyme activity was reported as 1‒5 µmol/g prot/h for glucocerebrosidase and 4‒80 µmol/L/h for chitotriosidase.11

Of the 5128 suspected cases of Gaucher disease, 882 patients (17%) were diagnosed with the disease. Most of these patients (81.5% [719/882]) showed positive parental consanguinity; the male to female ratio was 1.6 to 1. The age range for diagnosis was from 3 months to 45 years, with 97.5% of patients diagnosed between the ages of 1.7 to 8 years. A decrease in the activity of glucocerebrosidase was evident in 99% of patients diagnosed with Gaucher disease. The mean glucocerebrosidase activity value in these patients represented 0.3 µmol/g prot/h, which was 30% of the low normal value. In these patients, chitotriosidase activity levels were increased (mean [standard deviation (SD)] 6243 [20,211] µmol/L/h). However, in nine patients, chitotriosidase levels were zero, and glucocerebrosidase activity was 45% of the low normal value.11

In 103 cases of suspected Gaucher disease, an elevation in mean (SD) chitotriosidase activity (131.8 [24.0] µmol/L/h) was noted; however, mean glucocerebrosidase (3.2 µmol/g prot/h) levels were normal.11

C-ANPROM/INT//7567; Date of preparation: September 2020