1. Genetic testing for Gaucher disease

Gaucher disease

November 24, 2017

Clinical features

Gaucher disease (GD) is a rare genetic disorder characterized by the deposition of glucocerebroside in cells of the macrophage-monocyte system. The disorder results from the deficiency of the enzyme glucocerebrosidase. The prevalence of GD is approximately 1 in 57,000 to 1 in 75,000 worldwide 1, 2 but the disease is more prevalent in individuals of Ashkenazi Jewish descent in whom the incidence is 1 in 800 3, 4.

Gaucher disease encompasses a continuum of clinical findings ranging from perinatal lethal to asymptomatic. The identification of three major clinical types (1, 2, and 3) and two other subtypes (perinatal-lethal and cardiovascular) is useful in making a prognosis and management of the disease. Gaucher disease Type 1 is also known as non-neuronopathic Gaucher disease.

Type I is the most common form of Gaucher disease and lacks primary central nervous system involvement. Patients have highly variable phenotype, Some might be asymptomatic, while others may manifest following symptoms in childhood: painless splenomegaly, thrombocytopenia, anemia, pancytopenia. Bleeding secondary to thrombocytopenia may manifest as nosebleeds, bruising, or both. Patients may also have chronic fatigue, hepatomegaly, bone pain, or pathologic fractures. Clinical or radiographic evidence of bone disease occurs in 70-100% of individuals with GD type 1. Bone disease ranges from asymptomatic osteopenia to focal lytic or sclerotic lesions and osteonecrosis 5. The most debilitating aspect of type 1 GD is bone pain, pathologic fractures, and subchondral joint collapse with secondary degenerative arthritis. Further, neurologic complications, resulting from spinal cord or nerve root compression, may appear secondary to bone disease. Pulmonary involvement is another common finding in GD type 1. It includes interstitial lung disease, alveolar/lobar consolidation, and pulmonary hypertension.

GD type 1 and GD type 2 are characterized by neuronopathic involvement: type 2 is known as acute neuronopathic GD, while type 3 is known as subacute neuronopathic GD.

Affected children with onset before age two years show a rapidly progressive course, limited psychomotor development, and death by age two to four years 1. Individuals with type 3 GD usually have a more slowly progressive course of disease, with life span extending into the third or fourth decade 1. Major neurological signs and symptoms observed in GD patients include the following:

  • Bulbar signs (stridor, squint, and swallowing difficulty)
  • Pyramidal signs (opisthotonus, head retroflexion, spasticity, and trismus)
  • Oculomotor involvement, including oculomotor apraxia, saccadic initiation failure, and opticokinetic nystagmus
  • Generalized tonic-clonic seizures and progressive myoclonic epilepsy, and ataxia.

In a subset of GD patients one of the dominant clinical findings is cardiovascular disease which includes calcification of the mitral and aortic valves 1.

Another form of Gaucher disease is the perinatal-lethal form, which is associated with hepatosplenomegaly, pancytopenia, and microscopic skin changes and may present clinically as nonimmune hydrops fetalis or with ichthyosiform. Arthrogryposis and distinctive facial features are seen in 35-43% of perinataly affected GD patients 6. A rare severe variant of GD is associated with hydrocephalus, corneal opacities, deformed toes, gastroesophageal reflux, and fibrous thickening of splenic and hepatic capsules 7.

Gaucher disease is caused by homozygous or compound heterozygous pathogenic variants in the gene encoding acid beta-glucosidase (GBA) on chromosome 1q22 1. The deficient activity of beta-glucocerebrosidase results in the intracellular accumulation of glucosylceramide (GlcCer, glucosylcerebroside) primarily within cells of mononuclear phagocyte origin, which can be identified in most tissues of the body (characteristic 'Gaucher cells') 1.

The most efficient and reliable method of establishing a diagnosis of GD is the biochemical assay of glucocerebrosidase enzyme activity in peripheral blood leukocytes. This fluorometric assay uses the substrate 4-methylumbelliferyl-β-D-glucopyranoside and as a result of the test in affected individuals, glucocerebrosidase enzyme activity in peripheral blood leukocytes is 0-15% of normal activity 1.

In suspected individuals, bone marrow examination could be performed and can reveal the presence of lipid-engorged macrophages (Gaucher cells), characterized by a fibrillary and crumpled silk appearance to the cytoplasm and an eccentrically placed nucleus 1. Gaucher cells stain positively with periodic acid-Schiff reagent and have a cellular phenotype similar to alternatively activated macrophages 1.

Molecular genetic testing and analysis of the GBA gene is the most precise diagnostic method for the detection of GD. More than 300 distinct pathogenic variants of the GBA gene have been described, of which 77% are missense substitutions, while other types of variants account for the remaining (CentoMD®4.1, Figure 1).

Figure 1: Types of GBA clinically relevant variants on protein level (CentoMD®4.1)

Four common pathogenic variants in the GBA gene account for 89% of all familial Gaucher disease cases. N370S, L444P, 84GG, and IVS2+1 are the old nomenclatures; currently they are known with updated nomenclature based on different transcript used (according to GeneReviews 1; Table 1):

Table 1: Most common pathogenic variants in the GBA gene, causing 89% of all familial cases of Gaucher disease

Variant name Nucleotide change Amino acid change Reference sequences
IVS2+1G>A c.115+1G>A   NM_000157.3
84GG (84-85insG) c.84dupG p.Leu29AlafsTer18
N370S c.1226A>G p.Asn409Ser
L444P c.1448T>C p.Leu483Pro

These four most common pathogenic variants account for approximately 90% of the disease-causing alleles in the Ashkenazi Jewish population 1. In non-Jewish populations, these same four alleles account for approximately 50-60% of disease-causing alleles 1.

The features of Gaucher disease show overlap with some more common diseases, such as Parkinsons disease (PD). Pathogenic variants in GBA and alterations in glucosylceramide metabolism may be a risk factor for parkinsonism 1 :

  • GBA pathogenic variants have been identified in 5-10% of individuals with Parkinsons disease1, 10. PD associated with variants of GBA (GBA-PD) is clinically, pathologically, and pharmacologically indistinguishable from idiopathic “sporadic” PD, although GBA-PD has a slightly earlier onset (~5 years earlier) and more frequent cognitive dysfunction1, 10.
  • Brain pathology in some type 1 GD patients revealed astrogliosis and changes in the hippocampal regions. Brain pathology in individuals with type 2 and type 3 GD additionally revealed neuronal loss 1, 8.
  • Immunofluorescence staining on brain tissue samples from PD patients with identified GBA pathogenic variant showed the presence of glucocerebrosidase in 32-90% of Lewy bodies 8.
  • GBA enzyme activity was shown to be reduced in the substancia nigra in the brains of individuals with Parkinson disease (PD), confirming the relevance of enzyme function to the wider PD population 1, 8.
  • The estimated risk for individuals with Gaucher disease of developing PD is 20- to 30-fold the risk of an individual in the general population 1, 8.
  • Family studies suggest that the incidence of Parkinsonism may be higher in obligate heterozygotes for GD 9.

Enzyme replacement therapy (ERT) has completely revolutionized the treatment and prognosis for Gaucher disease and is now the standard of care for patients with this disease. Enzyme replacement therapy (ERT) consists of infusions of mannose-terminated glucocerebrosidase which have helped in the regression of many visceral manifestations of the disease. For those affected persons not receiving ERT or alternative substrate reduction therapy (SRT), there is a symptomatic treatment which includes partial or total splenectomy for massive splenomegaly and thrombocytopenia 1. Supportive care for all affected individuals may include: transfusion of blood products for severe anemia and bleeding, analgesics for bone pain, joint replacement surgery for relief from chronic pain and restoration of function, and oral bisphosphonates and calcium for osteoporosis 1.

CENTOGENE offers hotspot testing for the most common GBA pathogenic variants, full sequencing and deletion/duplication testing of the GBA gene. GBA is also part of the following CENTOGENE panels:

  • Lysosomal storage disease panel
  • Parkinsons disease panel
  • AllNeuro panel
  • CentoICU™ platinum plus
  • CentoICU™ platinum
  • Ashkenazi panel (basic)
  • Ashkenazi panel (advanced)

Differential diagnosis

The differential diagnosis of GBA related disorders – depending on the major symptoms in the initial case – includes the following diseases:

  • Hepatosplenomegaly, observed in Niemann-Pick disease (A, B and C), Wolman disease, Mucopolysaccharidoses, and oligosaccharidoses
  • Saposin C deficiency or prosaposin deficiency
  • Lysosomal storage diseases
  • Legg-Calvé-Perthes disease
  • Congenital ichthyoses and collodion skin changes
  • Myoclonic seizures
  • Hydrops fetalis.

Testing strategy

To confirm/establish the diagnosis, we offer full GBA gene sequencing and deletion/duplication gene testing. We also offer a broad selection of NGS panels which are designed for the molecular diagnostics of related conditions/phenotypes.

Thus, CENTOGENE offers the following testing strategy for GBA gene testing:

Step 1: Acid beta-glucosidase enzymatic activity testing

Step 2: Sequence analysis/pathogenic variant scanning for the GBA gene. GBA full gene sequencing – covers the entire coding region, exon/intron boundaries and 200 bp of the gene promoter.

Step 3: Deletion/duplication analysis of GBA if only heterozygous variant detected

Step 4: If no pathogenic variant is identified after analysis of the GBA gene, panel testing with related genes or further genetic testing of related genes can be done

Step 5: If no pathogenic variant is identified in any of the panel genes listed, we can offer whole exome sequencing, based on NGS technology

Referral reasons

The following individuals are candidates for GBA gene testing:

  • Individuals with a family history of Gaucher disease and presentation of the most common symptoms
  • Individuals without a positive family history, but with symptoms resembling Gaucher disease
  • Individuals with a negative but suspected family history, in order to perform proper genetic counseling (prenatal analyses are recommended in families with affected individuals).

Test utility

Sequencing, deletion/duplication of GBA gene and related genes should be performed in all individuals suspected of having this particular phenotype. In parallel, other genes reported to be related with this clinical phenotype should also be analyzed for the presence of pathogenic variants, due to the overlap in many clinical features caused by those particular genes.

Confirmation of a clinical diagnosis through genetic testing can allow for genetic counseling and may direct medical management. Genetic counseling can provide a patient and/or family with the natural history of the Gaucher disease, identify at-risk family members, provide information about reproductive risks as well as preconception/prenatal options, and allow for appropriate referral for patient support and/or resources.

Hotspots pathogenic variants characteristic for GBA gene

“Hotspot testing” offered by CENTOGENE always covers the most frequent and relevant pathogenic variants (NM_001005741.2; NP_001005741.1):

Nucleotide change Amino acid change dbSNP number (NCBI) HGMD accession
c.1226A>G p.N409S
(known as “N370S”)
rs76763715 CM880036
c.1448T>C p.L483P
(known as “L444P”)
rs421016 CM870010
c.84dupG Also known as “84GG” or “1035insG” rs387906315 CI910569
c.115+1G>A IVS2 ds G-A +1 No dbSNP ID CS920754

More information on CENTOGENE´s genetic tests for Gaucher disease can be found in our genetic test catalogue.