Novel mutation, L371V, causing multigenerational Gaucher disease in a Lebanese family

Three cases of multi-generational Gaucher disease and colon cancer from an Ashkenazi Jewish family: A lesson for cascade screening

Gaucher disease (GD) is one of the commonest lysosomal storage diseases that is inherited in an autosomal recessive manner and affects 1 in 50,000 to 100,000 people in the general population. The frequency is much higher (1 in 500 to 1000) in people of Ashkenazi Jewish heritage due to a founder effect. GD is caused by decreased or absent activity of β-glucosidase with subsequent accumulation of the substrate glucosylceramide in macrophages due to genetic alterations in the GBA gene. These often accumulate in the spleen, liver and bone marrow. Three types exist, with type 1 being the most common, also referred to as non-neuronopathic GD. A broad clinical spectrum exists; patients of any age may manifest with hepatosplenomegaly, anaemia, thrombocytopenia, lung disease, bone abnormalities or may remain asymptomatic throughout their lifespan. Multi-generational disease does not usually occur because the risk of disease with each pregnancy, presuming both parents are carriers of the condition, is 25%. Herein, we report an Ashkenazi Jewish family with multi-generational GD type 1 and multigenerational colon cancer in the same three individuals, and reinforce the importance of cascade screening in families with genetic conditions.

A novel genotype c.1228C>G/c.1448C-1498C (L371V/Rec-NciI) in a 3-year-old child with type 1 Gaucher disease

Gaucher disease (GD) is an autosomal recessive inborn error of metabolism, resulting from a deficiency of the enzyme glucocerebrosidase, causing an accumulation of the glycolipid glucocerebroside within lysosomes of macrophages in the reticuloendothelial system. Three major clinical forms have been assigned and more than 200 gene mutations have been identified. We herein report a Lebanese boy born with a novel combined mutation L371V/Rec-NciI, who presented with moderate-severe type 1 GD. An overview of the clinical and biomarker improvement following enzyme replacement therapy with imiglucerase is described in a follow-up of 30 months. Imiglucerase seems to be efficacious in decreasing the severity of the disease associated with this mutation. However, a high dose may be required to achieve optimal growth, platelet count, and hemoglobin level.

An evolutionary and structure-based docking model for glucocerebrosidase-saposin C and glucocerebrosidase-substrate interactions - relevance for Gaucher disease

Gaucher disease, the most prevalent lysosomal storage disorder, is principally caused by malfunction of the lysosomal enzyme glucocerebrosidase (GBA), a 497-amino acid membrane glycoprotein that catalyzes the hydrolysis of glucosylceramide to ceramide and glucose in the presence of an essential 84-residue activator peptide named saposin C (SapC). Knowledge of the GBA structure, a typical (beta/alpha)(8) TIM barrel, explains the effect of few mutations, directly affecting or located near the catalytic site. To identify new regions crucial for proper GBA functionality, we analyzed the interactions of the enzyme with a second (substrate) and a third (cofactor) partner. We build 3D docking models of the GBA-SapC and the GBA-ceramide interactions, by means of methodologies that integrate both evolutive and structural information. The GBA-SapC docking model confirm the implication of three spatially closed regions of the GBA surface (TIM barrel-helix 6 and helix 7, and the Ig-like domain) in binding the SapC molecule. This model provides new basis to understand the pathogenicity of several mutations, such as the prevalent Leu444Pro, and the additive effect of Glu326Lys in the double mutant Glu326Lys-Leu444Pro. Overall, 39 positions in which amino acid changes are known to cause Gaucher disease were localized in the GBA regions identified in this work. Our model is discussed in relation to the phenotype (pathogenic effect) of these mutations, as well as to the enzymatic activity of the recombinant proteins when available. Both data fully correlates with the proposed model, which will provide a new tool to better understand Gaucher disease and to design new therapy strategies.

Gaucher disease: different clinical manifestations associated with a rare mutation (R48W) in a Lebanese family

Gaucher disease (GD) is the most frequently encountered lysosomal storage disease, caused by autosomal recessive inborn defects in the glucocerebrosidase gene (GBA) at 1q21. The disease is most common in the Ashkenazi Jewish population. GD can present with a vast phenotypic heterogeneity, which can be predicted to some extent from the underlying mutation. In this report, we describe a Lebanese Arab family with multigenerational incidence of GD caused by a heterozygous genotype of a rare mutation, R48W, and a common one, L444P. Our patients' clinical course is described. We also review the English literature for patients with this rare mutation.

Analyses of variant acid beta-glucosidases: effects of Gaucher disease mutations

Acid beta-glucosidase (GCase) is a 497-amino acid, membrane-associated lysosomal exo-beta-glucosidase whose defective activity leads to the Gaucher disease phenotypes. To move toward a structure/function map for disease mutations, 52 selected single amino acid substitutions were introduced into GCase, expressed in an insect cell system, purified, and characterized for basic kinetic, stability, and activator response properties. The variant GCases from Gaucher disease patients and selected variant GCases from the mouse had decreased relative k(cat) and differential effects on active site binding and/or attachment of mechanism-based covalent (conduritol B epoxide) or reversible (deoxynojirimycin derivatives) inhibitors. A defect in negatively charged phospholipid activation was present in the majority of variant GCases but was increased in two, N370S and V394L. Deficits in saposin C enhancement of k(cat) were present in variant GCases involving residues 48-122, whereas approximately 2-fold increases were obtained with the L264I GCase. About 50% of variant GCases each had wild-type or increased sensitivity to in vitro cathepsin D digestion. Mapping of these properties onto the crystal structures of GCase indicated wide dispersion of functional properties that can affect catalytic function and stability. Site-directed mutagenesis of cysteine residues showed that the disulfide bonds, Cys(4)-Cys(16) and Cys(18)-Cys(23), and a free Cys(342) were essential for activity; the free Cys(126) and Cys(248) were not. Relative k(cat) was highly sensitive to a His substitution at Arg(496) but not at Arg(495). These studies and high phylogenetic conservation indicate localized and general structural effects of Gaucher disease mutations that were not obvious from the nature of the amino acid substitution, including those predicted to be nondisruptive (e.g. Val --> Leu). These results provide initial studies for the engineering of variant GCases and, potentially, molecular chaperones for therapeutic use.