**1. Introduction**

458 Etiology and Pathophysiology of Parkinson's Disease

Van der Kamp, W., Berardelli, A., Rothwell, JC., Thompson, PD., Day, BL. & Marsden, CD.

(1989) Rapid elbow movements in patients with torsion dystonia. *J. Neurol., Neurosurg. Psychiatry*, Vol. 52, No. 9, (September), 1043-1049, ISSN 0022-3050. von Krosigk, M., Smith, Y., Bolam, JP. & Smith, AD. (1992) Synaptic organization of

GABAergic inputs from the striatum and the globus pallidus onto neurons in the substantia nigra and retrorubral field which project to the medullary reticular formation. *Neuroscience*, Vol. 50, No. 3, (October), pp. 531-549, ISSN 0306-4522. Zweig, RM., Jankel, WR., Hedreen, JC., Mayeux, R. & Price, DL. (1989) The

pedunculopontine nucleus in Parkinson's disease. *Ann. Neurol.*, Vol. 26, No. 1,

Loss of pedunculopontine neurons in progressive supranuclear palsy. *Ann. Neurol.,*

Zweig, RM., Whitehouse, PJ., Casanova, MF., Walker, LC., Jankel, WR. & Price, DL. (1987)

(July)pp. 41-46, ISSN 0364-5134.

Vol. 22, No. 1SN 0364-5134.

The lysosome, initially discovered by Christian de Duve in 1955, is an intracellular organelle responsible of the ordered degradation of proteins, glycoproteins, proteoglycans, lipids, and other macromolecules originated from autophagy, endocytosis and phagocytosis. It is characterize by a limiting external membrane containing intraluminal vesicles. These organelles are estimated to contain 50-60 soluble acidic hydrolases (Journet et al., 2002), 55 membrane-associated proteins and 215 integral membrane proteins (Bagshaw et al., 2005). The macromolecules are scomposed by acid hydrolases in small molecules that are transported back in the cytosol by specific transporter proteins and then catabolized or reused by anabolic processes. Lysosomal hydrolases are synthetized as N-glycosylated precursors in the endoplasmatic reticulum and are transported to the lysosomes via a vectorial transport dependent on mannose 6-phosphate. Lysosomes are involved in many cellular processes like cholesterol homeostasis, autophagy, membrane repair, pathogen defense, cell signaling, apoptosys and bone/tissue remodelling; it is a foundamental organelle for cell life and not only the wastebasket of the cell. Microscopic identification of lysosomes is hard due to heterogeneity of organelles morphology dependent on their function as digestive organelles. The size and quantity of lysosomes varies in different cell types and can increase when the lysosomes accumulate non-digested material. Functional deficit of hydrolases, membrane-associated or integral membrane proteins causes lysosomal storage disorders (LSDs), a group of inherited metabolic pathologies characterized by intralysosomal deposition of undegraded macromolecules and by multisystemic phenotype (Saftig, 2006). The absence or reduced activity of a specific lysosomal hydrolase or other lysosomal proteins cause an abnormal function of the entire endosomal/lysosomal system (Bellettato & Scarpa, 2010).

More than 50 lysosomal storage disorders (LSD) are known with a total incidence of 1:7,000- 1:9,000 (Fletcher, 2006). Two thirds of them involve the central nervous system (Meikle et al.,

<sup>\*</sup>Chiara Balducci1, Silvia Paciotti1, Emanuele Persichetti1, Davide Chiasserini2, Anna Castrioto2, Nicola Tambasco2, Aroldo Rossi2, Paolo Calabresi2, Veronica Pagliardini3, Bruno Bembi4 and Lucilla Parnetti2

*<sup>1</sup>Dipartimento di SEEA, Università di Perugia, Italy*

*<sup>2</sup>Clinica Neurologica, Ospedale S. Maria della Misericordia, Università di Perugia, Italy* 

*<sup>3</sup>Dipartimento di Pediatria, Università di Torino, Italy 4Centro Regionale per le malattie Rare, Ospedale Universitario 'Santa Maria della Misericordia', Italy* 

Role of Lysosomal Enzymes in Parkinson's Disease: Lesson from Gaucher's Disease 461

1965). This enzyme is involved in the catabolic pathway of glycosphingolipids and is responsible for the cleavage of the β-glucosidic bond on the glucosylceramide (or

The human β-glucosidase is encoded by a gene (GBA) located on chromosome 1 (1q21) (Barneveld et al., 1983) which comprises 11 exons and 10 introns, spanning 7.6 kb of sequence. A non processed pseudogene (GBAP), which shares 96% exonic sequence homology, is located 16 kb downstream of the functional β-glucocerebrosidase gene

The lack of GCase activity leads to accumulation of glycolipid substrates, primarily glucocerebroside and its nonacylated analog, glucosylsphingosine, in all organs, particularly in spleen, liver, lungs and bone marrow (Cox & Shofield, 1997; Beutler & Grabowski, 2001). The material stored is the product of the arrested breakdown of gangliosides, glycosphingolipids and globosides, which derived from the cellular turnover of membranes.

Fig. 1. Involvement β-glucocerebrosidase in the catabolic pathway of glycosphingolipids

al., 2005; Futerman & van Meer, 2004) (Table 1).

Although in the patients the GCase is inactive in all cells, glucocerebroside accumulation occurs principally within the lysosomes of macrophages which adopt a characteristic "Gaucher's cell" morphology. Disease manifestations are related to the migration and accumulation of the Gaucher's cells, which displace healthy cells in the tissues. Furthermore the abnormal material stored in the cells of the reticuloendothelial system induces the release of inflammatory factors, including chemokines and cytokines, which leads to the cascade of pathological changes (Beutler & Grabowski, 2001; Cox, 2001; Aerts & Hollak, 1997; Moran et al., 2000; Jmoudiak & Futerman, 2005; Nilsson & Svennerhol, 1982; Pelled et

Gaucher's disease may occur at any age in any human population (Beutler & Grabowski, 2001; Zimran et al., 1992; Cox & Shofield, 1997; Erikson, 1986). Although the birth frequency

glucocerebroside) (Fig. 1).

(Horowitz et al., 1989).

1999). The LSD can be classified in sphingolipidoses, mucopolysaccharidoses, mucolipidoses, lipid storage disease, glycogen storage disease type II and lysosomal transport defects. Different LSD displayed different symptoms severity and different age onset and it depend on the organs affected and the residual enzyme activity. Generally, mutation leaving very low residual enzyme activity cause the most severe onset form of the pathologies; contrary higher residual enzyme activity delays disease onset (Kolter & Sandhoff, 1999). The disease course and severity are different in late-onset forms and can be variable even among affected siblings in the same family (Zhao & Grabowski, 2002). LSDs are often multisystemic disorders and many of these displayed a severe, progressive and untreatable neurological impairment. Almost all LSDs are related to devastating, progressive and untreatable effects on central nervous system (CNS). Neuronal loss occurs in the advanced stages of the diseases and is due to apoptosis or necrosis. The neurological symptoms are mental retardation, progressive neurodegeneration, dementia. Most LSDs show CNS involvment althought the undegraded material concentration is lower in the brain than in other organs. It seems that neurons are more vulnerable than other cellular type probably for a limited cell regeneration potential or for the absence of compensatory pathways (Bellettato & Scarpa, 2010). The Neuronal Ceroid Lipofuscinoses (NCLs) are lysosomal storage diseases affecting the CNS, with progressive loss of vision, decreasing cognitive and motor skills, epileptic seizures and premature death, with dementia without visual loss prominent in the rarer adult forms (Kohan et al., 2011). GM1 type 3 Gangliosidosis is an autosomal recessive lysosomal storage disorder caused by *β*galactosidase deficiency, patients were recently found to be affected by generalized dystonia associated to akinetic-rigid parkinsonism (Roze et al., 2005). The San Filippo Syndrome type B is a LSDs due to mutation in the gene encoding -N-acetylglucosaminidase with an accumulation of heparan sulfate. Affected children shown mental retardation, dementia, behavior problems. The analysis of mutant mice showed cytoplasmic inclusion of P-tau aggregates, characteristic of tauopathies, a group of age-related dementia that include Alzheimer disease (Ohmi et al., 2009).

In some adult neurodegenerative disorders like Alzheimer's disease, Parkinson's disease and Huntington' s disease the clical features are similar to those found in LSDs: accumulation of undegraded material, abnormal inflammatory response in the brain and changes in neurons morphology and functionality (Bellettato et al., 2010). In Parkinson's disease was found an involvement of cathepsin D, a lysosomal enzyme, in -synuclein degradation and formation of carboxy-terminally truncated -synuclein. Recent works suggest that impaired cathepsin D activity would result in incresed a-synuclein levels that cause its aggregation (Sevlever et al., 2008). In Huntington's disease N-terminal mutant huntingtin fragments form inclusions that lead to cell death. Some protease, like cathepsin D, B and L, help to degrade mutant huntingtin but increase N-terminal fragment formation and inclusions deposition inducing neuronal disruption (Kim et al., 2006).

### **2. Gaucher's disease: An overview**

Gaucher's disease (GD) is an inherited autosomal recessive metabolic disorder, resulting from a deficiency of the lysosomal enzyme β-glucocerebrosidase (also called acid βglucosidase, GCase) (EC 3.2.1.45).

GD was first described as a systemic disease by Philippe Gaucher in 1882, but only in 1965 this disorder was related to the deficiency of β-glucocerebrosidase (Patrick, 1965; Brady et al.

1999). The LSD can be classified in sphingolipidoses, mucopolysaccharidoses, mucolipidoses, lipid storage disease, glycogen storage disease type II and lysosomal transport defects. Different LSD displayed different symptoms severity and different age onset and it depend on the organs affected and the residual enzyme activity. Generally, mutation leaving very low residual enzyme activity cause the most severe onset form of the pathologies; contrary higher residual enzyme activity delays disease onset (Kolter & Sandhoff, 1999). The disease course and severity are different in late-onset forms and can be variable even among affected siblings in the same family (Zhao & Grabowski, 2002). LSDs are often multisystemic disorders and many of these displayed a severe, progressive and untreatable neurological impairment. Almost all LSDs are related to devastating, progressive and untreatable effects on central nervous system (CNS). Neuronal loss occurs in the advanced stages of the diseases and is due to apoptosis or necrosis. The neurological symptoms are mental retardation, progressive neurodegeneration, dementia. Most LSDs show CNS involvment althought the undegraded material concentration is lower in the brain than in other organs. It seems that neurons are more vulnerable than other cellular type probably for a limited cell regeneration potential or for the absence of compensatory pathways (Bellettato & Scarpa, 2010). The Neuronal Ceroid Lipofuscinoses (NCLs) are lysosomal storage diseases affecting the CNS, with progressive loss of vision, decreasing cognitive and motor skills, epileptic seizures and premature death, with dementia without visual loss prominent in the rarer adult forms (Kohan et al., 2011). GM1 type 3 Gangliosidosis is an autosomal recessive lysosomal storage disorder caused by *β*galactosidase deficiency, patients were recently found to be affected by generalized dystonia associated to akinetic-rigid parkinsonism (Roze et al., 2005). The San Filippo Syndrome type B is a LSDs due to mutation in the gene encoding -N-acetylglucosaminidase with an accumulation of heparan sulfate. Affected children shown mental retardation, dementia, behavior problems. The analysis of mutant mice showed cytoplasmic inclusion of P-tau aggregates, characteristic of tauopathies, a group of age-related dementia that include

In some adult neurodegenerative disorders like Alzheimer's disease, Parkinson's disease and Huntington' s disease the clical features are similar to those found in LSDs: accumulation of undegraded material, abnormal inflammatory response in the brain and changes in neurons morphology and functionality (Bellettato et al., 2010). In Parkinson's disease was found an involvement of cathepsin D, a lysosomal enzyme, in -synuclein degradation and formation of carboxy-terminally truncated -synuclein. Recent works suggest that impaired cathepsin D activity would result in incresed a-synuclein levels that cause its aggregation (Sevlever et al., 2008). In Huntington's disease N-terminal mutant huntingtin fragments form inclusions that lead to cell death. Some protease, like cathepsin D, B and L, help to degrade mutant huntingtin but increase N-terminal fragment formation

Gaucher's disease (GD) is an inherited autosomal recessive metabolic disorder, resulting from a deficiency of the lysosomal enzyme β-glucocerebrosidase (also called acid β-

GD was first described as a systemic disease by Philippe Gaucher in 1882, but only in 1965 this disorder was related to the deficiency of β-glucocerebrosidase (Patrick, 1965; Brady et al.

and inclusions deposition inducing neuronal disruption (Kim et al., 2006).

Alzheimer disease (Ohmi et al., 2009).

**2. Gaucher's disease: An overview** 

glucosidase, GCase) (EC 3.2.1.45).

1965). This enzyme is involved in the catabolic pathway of glycosphingolipids and is responsible for the cleavage of the β-glucosidic bond on the glucosylceramide (or glucocerebroside) (Fig. 1).

The human β-glucosidase is encoded by a gene (GBA) located on chromosome 1 (1q21) (Barneveld et al., 1983) which comprises 11 exons and 10 introns, spanning 7.6 kb of sequence. A non processed pseudogene (GBAP), which shares 96% exonic sequence homology, is located 16 kb downstream of the functional β-glucocerebrosidase gene (Horowitz et al., 1989).

The lack of GCase activity leads to accumulation of glycolipid substrates, primarily glucocerebroside and its nonacylated analog, glucosylsphingosine, in all organs, particularly in spleen, liver, lungs and bone marrow (Cox & Shofield, 1997; Beutler & Grabowski, 2001). The material stored is the product of the arrested breakdown of gangliosides, glycosphingolipids and globosides, which derived from the cellular turnover of membranes.

Fig. 1. Involvement β-glucocerebrosidase in the catabolic pathway of glycosphingolipids

Although in the patients the GCase is inactive in all cells, glucocerebroside accumulation occurs principally within the lysosomes of macrophages which adopt a characteristic "Gaucher's cell" morphology. Disease manifestations are related to the migration and accumulation of the Gaucher's cells, which displace healthy cells in the tissues. Furthermore the abnormal material stored in the cells of the reticuloendothelial system induces the release of inflammatory factors, including chemokines and cytokines, which leads to the cascade of pathological changes (Beutler & Grabowski, 2001; Cox, 2001; Aerts & Hollak, 1997; Moran et al., 2000; Jmoudiak & Futerman, 2005; Nilsson & Svennerhol, 1982; Pelled et al., 2005; Futerman & van Meer, 2004) (Table 1).

Gaucher's disease may occur at any age in any human population (Beutler & Grabowski, 2001; Zimran et al., 1992; Cox & Shofield, 1997; Erikson, 1986). Although the birth frequency

Role of Lysosomal Enzymes in Parkinson's Disease: Lesson from Gaucher's Disease 463

leads to impaired function of large joints, including hip, knee, and shoulder. Other bone symptoms include local swelling (Gaucheromas) and osteolysis as well as generalized demineralization and osteoporosis with consequent risk of fractures. Furthermore patients may show abnormal diffuse yellow-brawn skin pigmentation and delays of growth, menarche and dentition. In rare cases there can be also renal involvement, pulmonary

Type 2 (OMIM 230900) is the most severe form of Gaucher's disease which accounts for fewer than 1% cases. It manifests in early childhood; neurological deterioration progresses quickly and death generally occurs within the age of two years, in a context of psychomotor decline (Brady et al., 1993). The majority of cases of type 2 GD emerges around age of 3 months. The presenting sign is usually hepatosplenomegaly. By 6 months, neurologic complications develop. The first diagnostic simptoms are frequently supranuclear horizontal oculomotor paralysis or bilateral fixed strabismus accompanied by trismus, retroflection of the head, progressive spasticity, hyperreflexia, positive Babinski signs and other phatologic reflexes. Other symptoms can be dysphagia and difficulty in handling secretions developed, often followed by aspiration pneumonia. Death occurs by either

Gaucher's disease type 3 (OMIM 231000) is particularly frequent in Norbottnian Swedes (Erikson, 1986). It leads to subacute neurological symptoms that are less severe than those of type 2 disease. It is characterized by the presence of a later onset and a slow progressive neurological syndrome. The clinical manifestations vary. Systemic symptoms precede neurologic abnormalities and usually are similar to those seen in type 1 GD. Neurologic deterioration includes cerebellar ataxia, spastic paraperesis, psychomotor seizures,

Over 300 mutations of the β-glucosidase gene have been described (Beutler & Gelbart, 1996; Geabowski & Horowitz, 1997, Hruska et al., 2008). The most common are c.1226A>G (N370S), c.1448T>C (L444P), IVS2+1G>A and 84insG. The frequency and distribution of mutations vary with the population studied; in the Ashkenazi population N370S is found in 78% of patients whereas in non-Jewish populations the most frequent mutation is L444P

Although molecular analysis of the glucocerebrosidase gene in patients with Gaucher's disease has permitted broad correlations between genotype and phenotype, this does not consent a confident prediction of clinical phenotype (Cox & Sholfield, 1997; Germain, 2004). Many studies have shown the enormous clinical variation between patients who have the same genotype including monozygotic twins (Sidransky, 2004; Lachmann et al., 2004). Nevertheless the presence of N370S on one or both alleles is associated with type 1 GD and it seems to protect against neurological symptoms, except for Parkinson-like syndromes (Charrow et al., 2000; Cherin et al., 2006). On the contrary the presence of the L444P/L444P mutation is associated with the development of neurological manifestations, above all in Gaucher's disease type 3 (75% of cases) (Charrow et al., 2000). Other mutations, including 84insG, IVS2+1G>A, c.754T>A (F213I) and c.1297G>T (V394L), are generally responsible for the emergence of a neurological form, when associated with mutation L444P either alone or

Parkinson's disease (PD) is the one of the common movement disorders and the second most common human neurodegenerative disease. The major diagnostic neuropathological

horizontal supranuclear ophthalmoplegia, myoclonic epilepsy and dementia.

**3. Gaucher's and Parkinson's disease: Theories of a link** 

hypertension (Theise & Ursell, 1990), and cardiac abnormalities.

apnea or aspiration pneumonia.

integrated in a complex allele.

(36%), followed by N370S (29%) (Beutler, 2006).

of Gaucher's disease is one case per 60,000 live births in the general population (Meikle et al., 1999), it is the most frequent genetic disease in the Ashkenazi Jewish people where epidemiological data, based on estimated gene frequencies, show a prevalence of one case per 850 live births (Beutler et al., 1993).

GD has a highly variable phenotype, and even though a recent trend is to consider GD as a continuum of disease states (Goker-Alpan et al., 2003), three basic clinical forms are conventionally distinguished on the basis of the neurological involvement: the non neuronopathic form (type 1), the acutely neuronopathic form (type 2) and the subacute neurophatic form (type 3).

Table 1. Macrophage secretory products icreased in Gaucher's disease

Type 1 GD (OMIM 230800) is the most frequent form of Gaucher's disease and account 94% of all registered cases according to Gaucher Registry. It is a chronic multisystem storage disorder which, by definition, does not involve the central nervous system. Nevertheless recent studies have shown a possible correlation between type 1 GD and some neurological manifestations (Sindransky, 2004; Cherin, 2006; Biegstraaten et al., 2008). In a number of cases these symptoms can be the consequence of secondary complications of the primary disease (e.g. compression of bone marrow or root nerve as a result of vertebral crush fractures caused by osteonecrosis), whereas in other ones they can be the product of specific GBA gene mutations, particularly in patients presenting parkinsonian syndromes (Aharon-Peretz et al., 2004; Bembi et al., 2003; Clark et al., 2005; Gan-Or et al., 2008; Machaczka et al., 1999; McKeran et al., 1985; Tayeby et al. 2003; Ziegler et al. 2007).

The type 1 GD course is slowly progressive. Generally the symptoms develop in adulthood even though various clinical manifestation may emerge in childhood. The clinical spectrum is vast and includes the complete absence of symptoms as well as the severe organ involvement with disability and occasionally fatal outcome. The patients show hepatosplenomegaly, with thrombocytopenia, anemia and leucopenia. Although in most patients these complications are not life-threatening and may go unrecognized for many years (some subjects remain asymptomatic up to the age of 70 or 80 years) (Berrebi et al., 1984), in other ones this metabolic defect can cause bruising, bleeding and high risk of infection as consequence of pancytopenia and respiratory insufficiency due to diffuse infiltration of Gaucher's cells into the alveolar spaces, perivascular, peribronchial, and into the septal regions (Schneider et al., 1977; Lee, 1982). Asthenia and fatigability are constant and seem independent of anemia, but rather to reflect an alteration of basal metabolism and cytokine secretion (Allen et al., 1997). Moreover degenerative changes in skeleton are the leading cause of bone pain and disability in patients with type 1 disease. The infiltration of Gaucher's cells in the bone marrow causes osteonecrosis, particularly during growth and

of Gaucher's disease is one case per 60,000 live births in the general population (Meikle et al., 1999), it is the most frequent genetic disease in the Ashkenazi Jewish people where epidemiological data, based on estimated gene frequencies, show a prevalence of one case

GD has a highly variable phenotype, and even though a recent trend is to consider GD as a continuum of disease states (Goker-Alpan et al., 2003), three basic clinical forms are conventionally distinguished on the basis of the neurological involvement: the non neuronopathic form (type 1), the acutely neuronopathic form (type 2) and the subacute

Interleukin-1b, TNFa Diverse host defence: fever, weight loss Interleukin 6 Acute phase response, B-cell stimulation, bone

Type 1 GD (OMIM 230800) is the most frequent form of Gaucher's disease and account 94% of all registered cases according to Gaucher Registry. It is a chronic multisystem storage disorder which, by definition, does not involve the central nervous system. Nevertheless recent studies have shown a possible correlation between type 1 GD and some neurological manifestations (Sindransky, 2004; Cherin, 2006; Biegstraaten et al., 2008). In a number of cases these symptoms can be the consequence of secondary complications of the primary disease (e.g. compression of bone marrow or root nerve as a result of vertebral crush fractures caused by osteonecrosis), whereas in other ones they can be the product of specific GBA gene mutations, particularly in patients presenting parkinsonian syndromes (Aharon-Peretz et al., 2004; Bembi et al., 2003; Clark et al., 2005; Gan-Or et al., 2008; Machaczka et al.,

The type 1 GD course is slowly progressive. Generally the symptoms develop in adulthood even though various clinical manifestation may emerge in childhood. The clinical spectrum is vast and includes the complete absence of symptoms as well as the severe organ involvement with disability and occasionally fatal outcome. The patients show hepatosplenomegaly, with thrombocytopenia, anemia and leucopenia. Although in most patients these complications are not life-threatening and may go unrecognized for many years (some subjects remain asymptomatic up to the age of 70 or 80 years) (Berrebi et al., 1984), in other ones this metabolic defect can cause bruising, bleeding and high risk of infection as consequence of pancytopenia and respiratory insufficiency due to diffuse infiltration of Gaucher's cells into the alveolar spaces, perivascular, peribronchial, and into the septal regions (Schneider et al., 1977; Lee, 1982). Asthenia and fatigability are constant and seem independent of anemia, but rather to reflect an alteration of basal metabolism and cytokine secretion (Allen et al., 1997). Moreover degenerative changes in skeleton are the leading cause of bone pain and disability in patients with type 1 disease. The infiltration of Gaucher's cells in the bone marrow causes osteonecrosis, particularly during growth and

Interleukin 8 Granulocyte chemoattractant Interleukin 10 Inhibits pro-inflammatory cytokines

Table 1. Macrophage secretory products icreased in Gaucher's disease

1999; McKeran et al., 1985; Tayeby et al. 2003; Ziegler et al. 2007).

resorption, trophic for mieloma cells

per 850 live births (Beutler et al., 1993).

Products Functions Lysozyme Antibacterial Angiotensin-converting enzyme Vasopressor Lysosomal acid hydrolases Digestion

neurophatic form (type 3).

leads to impaired function of large joints, including hip, knee, and shoulder. Other bone symptoms include local swelling (Gaucheromas) and osteolysis as well as generalized demineralization and osteoporosis with consequent risk of fractures. Furthermore patients may show abnormal diffuse yellow-brawn skin pigmentation and delays of growth, menarche and dentition. In rare cases there can be also renal involvement, pulmonary hypertension (Theise & Ursell, 1990), and cardiac abnormalities.

Type 2 (OMIM 230900) is the most severe form of Gaucher's disease which accounts for fewer than 1% cases. It manifests in early childhood; neurological deterioration progresses quickly and death generally occurs within the age of two years, in a context of psychomotor decline (Brady et al., 1993). The majority of cases of type 2 GD emerges around age of 3 months. The presenting sign is usually hepatosplenomegaly. By 6 months, neurologic complications develop. The first diagnostic simptoms are frequently supranuclear horizontal oculomotor paralysis or bilateral fixed strabismus accompanied by trismus, retroflection of the head, progressive spasticity, hyperreflexia, positive Babinski signs and other phatologic reflexes. Other symptoms can be dysphagia and difficulty in handling secretions developed, often followed by aspiration pneumonia. Death occurs by either apnea or aspiration pneumonia.

Gaucher's disease type 3 (OMIM 231000) is particularly frequent in Norbottnian Swedes (Erikson, 1986). It leads to subacute neurological symptoms that are less severe than those of type 2 disease. It is characterized by the presence of a later onset and a slow progressive neurological syndrome. The clinical manifestations vary. Systemic symptoms precede neurologic abnormalities and usually are similar to those seen in type 1 GD. Neurologic deterioration includes cerebellar ataxia, spastic paraperesis, psychomotor seizures, horizontal supranuclear ophthalmoplegia, myoclonic epilepsy and dementia.

Over 300 mutations of the β-glucosidase gene have been described (Beutler & Gelbart, 1996; Geabowski & Horowitz, 1997, Hruska et al., 2008). The most common are c.1226A>G (N370S), c.1448T>C (L444P), IVS2+1G>A and 84insG. The frequency and distribution of mutations vary with the population studied; in the Ashkenazi population N370S is found in 78% of patients whereas in non-Jewish populations the most frequent mutation is L444P (36%), followed by N370S (29%) (Beutler, 2006).

Although molecular analysis of the glucocerebrosidase gene in patients with Gaucher's disease has permitted broad correlations between genotype and phenotype, this does not consent a confident prediction of clinical phenotype (Cox & Sholfield, 1997; Germain, 2004). Many studies have shown the enormous clinical variation between patients who have the same genotype including monozygotic twins (Sidransky, 2004; Lachmann et al., 2004). Nevertheless the presence of N370S on one or both alleles is associated with type 1 GD and it seems to protect against neurological symptoms, except for Parkinson-like syndromes (Charrow et al., 2000; Cherin et al., 2006). On the contrary the presence of the L444P/L444P mutation is associated with the development of neurological manifestations, above all in Gaucher's disease type 3 (75% of cases) (Charrow et al., 2000). Other mutations, including 84insG, IVS2+1G>A, c.754T>A (F213I) and c.1297G>T (V394L), are generally responsible for the emergence of a neurological form, when associated with mutation L444P either alone or integrated in a complex allele.
