III. BACKGROUND 
A. GAUCHER DISEASE 
The lysosome is an organelle containing the enzymatic machinery needed to degrade 
macromolecules to soluble products which may be either excreted or reutil ized (1) . Inherited 
mutations in the genes coding lysosomal enzymes result in deficiencies of these activities 
and consequent storage of their substrates within the organel le' 2 ' 61 . In patients with Gaucher 
disease, a lysosomal B-gl ucosidase is deficient which results in the lysosomal storage of 
a complex glycol ipid called glucosylceramide (trivial names: glucosylceramide = 
gl ucocerebroside; acid-B-glucosidase = glucocerebrosidase)' 7 ' 81 . 
On the basis of clinical signs and symptoms, Gaucher disease has been divided into 
three subtypes: type 1 (nonneuronopathic) , type 2 (acute neuronopathic) , and type 3 
(subacute neuronopathic). All three types of Gaucher disease are caused by a deficiency 
of glucocerebrosidase resulting in the accumulation of glucosylceramide within the cells 
of the reticuloendothelial system 191 . The principal difference between the subtypes is the 
presence and progression of neurologic complications. A summary of subtypes of Gaucher 
disease and a review of the disorder is provided in the appendix. 
B. GLUCOCEREBROSIDASE 
Glucocerebrosidase (E3.2.1.45) (GC) is a monomeric, membrane - associated, hydrophobic 
glycoprotein with a molecular mass of 65000 daltons. Human GC protein consists of 497 amino 
acids. The enzyme is translated as a precursor protein with a 19 amino acid hydrophobic 
signal peptide which directs its co-transl ational insertion into the lumen of the 
endoplasmic reticul um-golgi -lysosome complex 1101 . GC acts at the acidic pH of the lysosomal 
environment to hydrolyze beta-glucosidic linkages in complex lipids. The catalytic activity 
is increased by detergents, lipids and a naturally occurring activator protein known as 
sphingolipid activator protein-2 (SAP-2 or saposin C)' 11,121 . Human GC cDNA was first cloned 
from a hepatoma cDNA library expressed in lambda gtll by screening with a polyclonal 
antibody developed to purified human placental GC 1131 . Subsequent characterizations of a 
number of separately isolated GC CDNA clones have described the complete nucleotide 
sequence 114,151 . The glucocerebrosidase gene has been localized to human chromosome 1 q21 by 
in situ hybridization 1161 . Analysis of genomic clones has shown the GC gene to consist of 
11 exons and 10 introns spanning approximately 7KB. A pseudogene is present in tandem with 
the active gene 06 ' 18 ’. 
Deficiency of glucocerebrosidase is the cause of Gaucher disease' 7,81 . More than twenty 
mutations in the gene are known, but only two are common' 191 . These two account for 
approximately 80% of the mutant alleles' 201 . A third mutation has recently been reported and 
is believed to occur in 20% of type 1 Gaucher patients' 211 . The several diseases grouped 
under the eponym of GD are inherited in an autosomal recessive pattern and each disease is 
j caused by a deficiency in the lysosomal acid hydrolase responsible for the catabolism of 
glucosylceramide' 91 . Although glucocerebrosidase is deficient in all cells, for unknown 
reasons, the accumulation of glucosylceramide occurs virtually only in macrophages. Storage 
i within only one cell type is unique among the lysosomal storage diseases. This 
I characteristic of the pathobiology of Gaucher disease has allowed the development of two 
treatment strategies based on the correction of enzyme deficiency in macrophages. The first 
approach to be of clinical benefit was allogeneic bone marrow transplantation which results 
I in the repopulation of affected tissues with enzyme-competent macrophages' 22,231 . Transplanted 
patients improve after engraftment of donor marrow and gradually resolve their 
j organomegaly' 241 . The second approach to result in clinical improvement in Gaucher disease 
j patients was macrophage-targeted enzyme replacement’ 261 . This method took advantage of 
j naturally occurring mannose receptors on macrophages and the exposition of accessible 
mannose residues in the oligosaccharides of glucocerebrosidase to effect an efficient, 
I targeted delivery of the enzyme to macrophages’ 25,261 . Patients have responded to this 
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