Three novel beta-galactosidase gene mutations in Han Chinese patients with GM1 gangliosidosis are correlated with disease severity

Abstract

Background: GM1 gangliosidosis (GM1) is an autosomal recessive lysosomal storage disease caused by deficiency of acid beta-galactosidase (GLB1; EC3.2.1.23). Here, we identify three novel mutations in the GLB1 gene from two Han Chinese patients with GM1 that appear correlated with clinical phenotype.

Methods: One of the two Han Chinese patients with GM1 presented with the juvenile form, and the other with the infantile form with cardiac involvement. Sequencing of the entire GLB1 gene revealed three novel mutations (p.H102 D, p.G494V, c.495_497delTCT), which were absent in 94 normal controls. Transient expression of cDNA encoding these variants was performed in COS-1 cells to evaluate β-galactosidase activities.

Results: The first case (patient 1) with the juvenile form contained two missense mutations, p.H102 D and p.A301V. Patient 2 diagnosed with the infantile form of the disease with cardiac involvement was compound heterozygous for p.G494V and c.495_497delTCT mutations. All mutant beta-galactosidases exhibited significantly reduced activity (12%, 0%, 0%, and 0% for p.H102 D, p.A301V, p.G494V, and c.495_497delTCT), compared with the wild-type beta-galactosidase cDNA clone. The mutations identified in patient 2 with cardiomyopathy were localized in the GLB1 gene region common to both lysosomal beta-galactosidase and elastin binding protein (EBP), and caused a deletion in the elastin-binding domain of EBP.

Conclusions: All four mutations identified in Han Chinese patients induce significant suppression of β-galactosidase activity, correlating with severity of disease and presence of cardiomyopathy.

Figure 1

Nucleotide sequences of the neighboring regions of the mutations in the GLB1 gene of two GM1 gangliosidosis patients. The mutant sequencing diagrams are shown. The position of each mutation is marked with an arrow (panels A-D). Wild-type and mutant nucleotide and amino acid sequences are presented using A of the ATG start codon of GLB1cDNA as position +1.

Figure 2

Schematic representation of alternatively spliced mRNA of the GLB1 gene encoding EBP. The unique 32 amino acid region encoded by a frameshift in exon 5 contains an elastin/laminin-binding domain (underlined). The 3 bp in-frame deletion resulting in p.S95del is enclosed within a square.

Figure 3

Alignment of the GLB1 homologs of six species around the H102 D variants indicated by squares http://www.ebi.ac.uk/Tools/clustalw/index.html. *Total sequence homology;: Very high homology;. High homology.