GM1 gangliosidosis: molecular analysis of nine patients and development of an RT-PCR assay for GLB1 gene expression profiling.

The human GLB1 gene produces two alternatively spliced transcripts that encode the lysosomal enzyme beta-galactosidase (GLB1) and the elastin binding protein (EBP). Mutations at the GLB1 locus, which are responsible for the storage disorder GM1 gangliosidosis, may affect either both proteins or GLB1 only. The EBP, when affected, contributes to specific features of GM1 gangliosidosis patients, such as cardiomyopathy and connective-tissue abnormalities. Here we report the development of reliable and quantitative assays based on real-time PCR for assessing the levels of GLB1 and EBP transcripts in patients' samples. We also report the characterisation of GLB1 gene mutations in nine GM1 gangliosidosis patients in order to correlate the genetic lesions with mRNA levels and phenotypes. Mutation analysis identified four new (c.1835_1836delCC; p.Arg148Cys; c.1068+1G>T; and p.Pro549Leu), five known (p.Arg59His; p.Arg201His; p.Gly123Arg; c.245+1G>A; and c.75+2insT) mutations and one new polymorphism (c.1233+8T>C). Comparative analysis of the patients' phenotypes enabled a more thorough correlation between GLB1 mutations and specific clinical manifestations. GLB1 and EBP mRNA levels were both reduced in three patients carrying the splicing defects. The accurate and fast method for the detection of alternatively spliced transcripts of the GLB1 gene could be applied to other disease-causing lysosomal genes that encode multiple mRNAs.