Why test for glucosylsphingosine (lyso-Gb1)?

Mutations in the GBA1 gene lead to a reduction in the enzymatic activity of glucocerebrosidase, causing accumulation of glucosylceramide in lysosomes.1 Glucosylsphingosine (lyso-Gb1) is a metabolic precursor of glucosylceramide synthesis, suggesting that the rate of accumulation and degradation of glucosylsphingosine (lyso-Gb1) may contribute to disease manifestations in patients with Gaucher disease. Therefore, glucosylsphingosine (lyso-Gb1) is useful as a biomarker for Gaucher disease.2,3

What is the glucosylsphingosine (lyso-Gb1) test?

Determination of free glucosylsphingosine (lyso-Gb1) can be obtained from EDTA plasma samples in patients undergoing biochemical analysis and genetic testing for Gaucher disease.3,4 Levels of glucosylsphingosine (lyso-Gb1) in dried blood spots have also been useful to aid in diagnosing patients with Gaucher disease. One study found that patients with neuronopathic Gaucher disease Types 2 or 3, exhibited significantly higher levels of glucosylsphingosine (lyso-Gb1) than patients with non-neuronopathic Gaucher disease Type 1. In addition to being a biomarker of Gaucher disease, glucosylsphingosine (lyso-Gb1) may be useful for prenatal diagnosis of the disease and in dried blood spot screening programmes.5

In patients with Gaucher disease Type 1 (n=64), levels of glucosylsphingosine (lyso-Gb1) are markedly increased in the plasma (median [range] 230.7 [15.6‒1035.2] nM) compared with individuals without Gaucher disease (n=28; median [range] 1.3 [0.8‒2.7] nM).3 Plasma glucosylsphingosine (lyso-Gb1) levels have also shown correlation with chitotriosidase (Spearman coefficient, p=0.66) and CC chemokine ligand 18 (CCL18) (p=0.40), which are produced by Gaucher cells and secreted into the circulation.3,6,7

The levels of glucosylsphingosine (lyso-Gb1) in the spleen of patients with Gaucher disease Type 1 are reportedly 54‒728 ng/mg protein. In patients with Gaucher disease Types 2 and 3, glucosylsphingosine (lyso-Gb1) levels are reported as 133‒1200 ng/mg protein and 109‒1298 ng/mg, respectively. Splenic levels of glucosylsphingosine (lyso-Gb1) are below 1 ng/mg protein in individuals without Gaucher disease. Moreover, brain levels of glucosylsphingosine (lyso-Gb1) are 22‒51-times and 38‒694-times higher in patients with Gaucher disease Type 3 and Gaucher disease Type 2, respectively, than individuals without Gaucher disease. Conversely, brain levels of glucosylsphingosine (lyso-Gb1) in patients with Gaucher disease Type 1 are within the normal range (1 ng/mg protein) and comparable to individuals without Gaucher disease (range, 0.04‒1.2 ng/mg protein). These data suggest that elevated levels of glucosylsphingosine (lyso-Gb1) may contribute to the disease manifestations of Gaucher disease.2

Glucosylsphingosine (lyso-Gb1) as a biomarker for paediatric Gaucher disease

The clinical charts of 81 patients aged <18 years with Gaucher disease from the Shaare Zedeck Medical Center in Israel, over a 4-year period, were reviewed to evaluate glucosylsphingosine (lyso-Gb1) as a biomarker for Gaucher disease in children. Disease severity was based on genotype: 35 patients had mild Gaucher disease Type 1; 34 had severe Gaucher disease Type 1; and 12 had Gaucher disease Type 3.8

At the time of last visit, glucosylsphingosine (lyso-Gb1) levels were significantly lower in children with mild Gaucher disease Type 1 versus those with severe Gaucher disease Type 1 (p=0.009); levels were comparable between patients with Gaucher disease Type 3 (p=0.81). With regards to age, gender, haemoglobin levels, liver or spleen volumes and platelet count, there were no significant differences between children with mild and severe Gaucher disease Type 1 (p>0.05). However, patients with Gaucher disease Type 3 had significantly larger liver (p=0.007) and spleen (p=0.005) volumes than children with Gaucher disease Type 1.8

In all cohorts combined, glucosylsphingosine (lyso-Gb1) levels significantly correlated with platelet count (p<0.0001) and haemoglobin levels (p=0.003), but not with liver or spleen volumes. There was no association between levels of glucosylsphingosine (lyso-Gb1) and age or weight. These data highlight that glucosylsphingosine (lyso-Gb1) appears to be a useful biomarker for children with Gaucher disease and can be included during routine follow-up.8

Glucosylsphingosine (lyso-Gb1) as a biomarker for adult Gaucher disease

The sensitivity and specificity of glucosylsphingosine (lyso-Gb1) as a biomarker for Gaucher disease was evaluated in 148 healthy adults (54.7% male; median age, 29 years) and compared with 98 genetically diagnosed patients with Gaucher disease (52.2% male; median age, 29 years), 13 carriers of Gaucher disease (64.7% male; median age, 35 years), and 261 patients with other lysosomal storage diseases (44.8% male; median age, 38 years).4

The levels of glucosylsphingosine (lyso-Gb1) across the four cohorts are presented in Figure 1. Only patients with Gaucher disease had glucosylsphingosine (lyso-Gb1) levels above the normal range: determined as a cut-off value of 12 ng/mL. This effect was independent of gender, with both male and female patients with Gaucher disease demonstrating elevated levels of glucosylsphingosine (lyso-Gb1) compared with individuals without Gaucher disease, carriers of Gaucher disease or patients with other lysosomal storage diseases.4

Figure 1.
Glucosylsphingosine (lyso-Gb1) levels in patients with Gaucher disease compared with healthy individuals, carriers of Gaucher disease and patients with other lysosomal storage diseases. Reproduced with permission from Rolfs A et al. PLoS One 2013; 8: e79732.4

Of the DNA data available, 45 different GBA1 mutations (see genetic inheritance of Gaucher disease) were identified in 98 patients with Gaucher disease. The most prevalent mutations were N370S (c.1226A>G; p.Asp409Ser, 32.5%), L444P (c.1448T>C; p.Leu483Pro, 22.1%) and RecNcil (c.1448T>C; 1483G>C; 1497G>C, 8.0%) which comprised approximately two-thirds of all mutations. Patients with Gaucher disease with the L444P (c.1448T>C; p.Leu483Pro) mutation had higher glucosylsphingosine (lyso-Gb1) levels (median, 184.5 ng/mL) than those with the N370S (c.1226A>G; p.Asp409Ser) mutation (median, 143.1 ng/mL). Moreover, median levels of glucosylsphingosine (lyso-Gb1) were higher in patients who had homozygous mutations (N370S/N370S, 143.1 ng/mL; L444P/L444P, 184.5 ng/mL) compared with heterozygous mutations (N370S, 77.1 ng/mL; L444P: 107.0 ng/mL). The accuracy of glucosylsphingosine (lyso-Gb1) as a biomarker for Gaucher disease was found to be significantly better than either chitotriosidase (p=0.027) or CCL18 (p<0.001).4

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