Five novel mutations in the lysosomal sialidase gene (NEU1) in type II sialidosis patients and assessment of their impact on enzyme activity and intracellular targeting using adenovirus-mediated expression

Abstract

Sialidosis is an autosomal recessive disease resulting from a deficiency of lysosomal sialidase. Type II sialidosis is a rare disease characterized clinically by hydrops fetalis, hepatosplenomegaly, and severe psychomotor retardation. Genomic DNA from four unrelated sialidosis patients was screened for mutations within the sialidase gene NEU1. Five novel mutations were identified. Four are missense and one is nonsense: c.674G>C (p.R225P), c.893C>T (p.A298V), c.3G>A (p.M1?), c.941C>G (p.R341G), and c.69G>A (p.W23X). We have used our findings and diagnostic tools to confirm the presence of a homozygous null allele in a neonate sibling. Recombinant adenoviruses expressing the mutant sialidase alleles in primary cell cultures were utilized to assess the impact of each mutation on enzyme activity and intracellular localization. None of the mutant alleles expressed significant enzymatic activity. The p.R341G mutation exerts its pathological effect by perturbing substrate binding, while the p.A298V and p.R225P mutations appear to impair the folding of the sialidase enzyme. Our findings point to mutation-sensitive amino acids involved in catalytic function or structural stability and indicate the potential utility of these mutations for molecular diagnosis of this rare disease.

Lysosomal Sialidase (Neuraminidase-1) Is Targeted to the Cell Surface in a Multiprotein Complex That Facilitates Elastic Fiber Assembly

“…In mammalian cells, four genetically distinct neuraminidases (sialidases) that differ in their tissue distribution, subcellular localization, and substrate specificity have been characterized. They have been localized to lysosomes (Neu1) (59,60), to the cytosol (Neu2) (67)(68)(69)(70)(71)(72), to the plasma membrane (Neu3, also known as ganglioside sialidase) (71,73,75,76), and to mitochondria (Neu4) (44,45); but only Neu1, expressed in all mammalian tissues and active mostly toward sialylated glycoproteins, has been detected in a multiprotein complex with ␤-galactosidase and PPCA (77)(78)(79).…”

“…Elastic cartilage fragments (source of chondrocytes) were obtained from a 1-year-old patient at the time of surgery for extirpation of pre-auricular tags. Because a functional deficiency of Neu1 occurs in two genetically distinct diseases (sialidosis, caused by primary lesions in the NEU1 gene (41)(42)(43)(44), and galactosialidosis, in which a combined secondary deficiency of Neu1 and ␤-galactosidase occurs as a result of a primary deficiency of PPCA) (45)(46)(47)(48), we also tested cells derived from patients with these diseases. Skin biopsies from three patients diagnosed with congenital sialidosis (patients 4028, 4029, and 4079) and three patients diagnosed with galactosialidosis (patients 5974, 5975, and 5976) were used.…”

Clinical and Serial MRI Findings of a Sialidosis Type I Patient with a Novel Missense Mutation in the <i>NEU1</i> Gene

“…Sialidosis type II is the early-onset form and is associated with macular cherry-red spots, the Hurler-like phenotype, dysostosis multiplex, short stature, developmental delays, mental retardation and hepatosplenomegaly (1,8,9). The age of onset and severity of the clinical manifestations are correlated with NEU1 mutations (10,11) and the level of residual neuraminidase activity (10,12,13), indicating the existence of considerable genotype-phenotype correlation in this disease. To date, more than 40 mutations within the NEU1 gene have been identified in patients with sialidosis type I or type II (2,3,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24).…”

Neuraminidase-1, a Subunit of the Cell Surface Elastin Receptor, Desialylates and Functionally Inactivates Adjacent Receptors Interacting with the Mitogenic Growth Factors PDGF-BB and IGF-2

“…1,2 In mammalian cells, four genetically distinct neuraminidases (sialidases), which differ in their tissue distribution, subcellular localization, and substrate specificity, have been characterized. They have been localized to lysosomes; neuraminidase 1 (Neu1) [3][4][5][6][7] to cytosol, neuraminidase 2 (Neu2) 8 -9 to the plasma membrane, neuraminidase 3 (Neu3, also known as ganglioside sialidase) 10 -12 to mitochondria and lysosomes, neuraminidase 4 (Neu4). [13][14][15] But only Neu1, which is expressed in all mammalian tissues and is active mostly toward sialylated glycoproteins, has been detected in a lysosome-targeted multiprotein complex with ␤-galactosidase (␤-Gal) and protective protein/cathepsin A (PPCA).…”