Protective protein gene mutations in galactosialidosis

Area of Science:

• Genetics
• Molecular Biology
• Biochemistry

Background:

• Galactosialidosis is a rare lysosomal storage disorder.
• It results from mutations in the protective protein (PP) gene, leading to deficiencies in beta-galactosidase and alpha-neuraminidase.
• Genetic heterogeneity contributes to diverse clinical presentations.

Purpose of the Study:

• To identify and characterize novel protective protein (PP) gene mutations in patients with galactosialidosis.
• To investigate the functional consequences of these mutations on enzyme activity and protein processing.
• To explore genotype-phenotype correlations in galactosialidosis.

Main Methods:

• Direct sequencing and restriction-site analysis of genomic DNA to identify mutations.
• Transient expression of mutant PP cDNA in a galactosialidosis cell line.
• Assays for beta-galactosidase and alpha-neuraminidase activity.
• Pulse-chase analysis to study protein processing and maturation.

Main Results:

• Four novel PP cDNA mutations (Q49R, W65R, S90L, Y395C) were identified in Japanese patients, and one (Y249N) in a French-German patient.
• The Y395C mutation was common in Japanese patients, with varying compound heterozygote combinations.
• Only the Y249N mutation partially restored beta-galactosidase and alpha-neuraminidase activity, showing some carboxypeptidase activity and producing a small amount of mature protein.
• Other mutations resulted in precursor protein accumulation without mature protein formation.

Conclusions:

• Identified mutations contribute to the genetic diversity of galactosialidosis.
• The Y249N mutation represents a unique case with partial functional restoration, offering insights into PP protein function.
• Understanding these mutations is crucial for diagnosing and potentially treating galactosialidosis.