The lysosomal storage disorders mucolipidosis type II, type III alpha/beta, and type III gamma: Update on GNPTAB and GNPTG mutations

Area of Science:

• Genetics
• Biochemistry
• Molecular Biology

Background:

• Mucolipidosis (ML) types II, III alpha/beta, and III gamma are inherited lysosomal storage disorders caused by mutations in GNPTAB and GNPTG genes.
• These genes encode subunits of N-acetylglucosamine (GlcNAc)-1-phosphotransferase, crucial for lysosomal enzyme targeting via mannose 6-phosphate signals.
• Defective enzyme function leads to macromolecule accumulation in lysosomes, impairing cellular processes and causing severe clinical manifestations.

Purpose of the Study:

• To provide a comprehensive overview of mutations in the GNPTAB and GNPTG genes associated with mucolipidosis.
• To report novel variants and analyze their functional impact on N-acetylglucosamine (GlcNAc)-1-phosphotransferase.
• To establish genotype-phenotype correlations for predicting clinical outcomes in ML patients.

Main Methods:

• Literature review of 564 reported cases of ML II and ML III.
• Identification and cataloging of 258 GNPTAB and 50 GNPTG mutations, including 58 novel GNPTAB and 7 novel GNPTG variants.
• Functional studies of GNPTAB missense mutations to elucidate enzyme function and structure.

Main Results:

• Detailed analysis of 258 GNPTAB and 50 GNPTG mutations, with the discovery of 58 new GNPTAB and 7 new GNPTG variants.
• Functional studies provided insights into the composition and activity of the GlcNAc-1-phosphotransferase enzyme.
• Established genotype-phenotype correlations to aid in predicting disease severity and clinical course.

Conclusions:

• The comprehensive mutation analysis and functional studies deepen the understanding of mucolipidosis pathogenesis.
• Identification of novel variants expands the mutational landscape of GNPTAB and GNPTG.
• Genotype-phenotype correlations derived from this study are valuable for clinical diagnosis and patient management.