Analysis of nonsense-mediated mRNA decay in mutant alleles identified in Spanish Gaucher disease patients.

Most of the mutations described in the GBA gene as responsible for Gaucher disease are missense mutations. Nevertheless, other alterations, including nonsense and frameshift mutations, have been reported. These mutations generate premature termination codons (PTC) that could trigger the degradation of mRNA through a mechanism known as nonsense-mediated decay (NMD). It has been established that NMD requires the presence of at least one intron downstream of the PTC, and that this PTC should be at least 50-55 nucleotides upstream of the 3'-most exon-exon junction. In this study, we analyse four GBA truncating mutations - c.108G > A (W(-4)X; HGVS recommended nomenclature: p.W36X), c.886C > T (R257X; HGVS: p.R296X), c.1098_1099insA and c.1451_1452delAC - found in Spanish Gaucher disease patients in order to determine whether they undergo mRNA decay and, if so, whether this occurs via the NMD pathway. RT-PCR showed a clear reduction of RNA for three of the alleles: W(-4)X, R257X and c.1098_1099insA. After treatment with cycloheximide (CHX), a known inhibitor of both protein synthesis and NMD, two of the mutant alleles, R257X and c.1098_1099insA, showed a partial recovery of the amount of mRNA. The third mutation, W(-4)X, did not show any significant CHX-induced recovery, while allele c.1451_1452delAC did not show mRNA decay at all. Real-time PCR confirmed these results and allowed the decay and recovery to be quantified. Finally, the protein truncation test was performed to detect the corresponding proteins. Expected products for alleles R257X, c.1451_1452delAC and c.1098_1099insA, but not for W(-4)X, were observed.