Two novel exonic point mutations in HEXA identified in a juvenile Tay-Sachs patient: Role of alternative splicing and nonsense-mediated mRNA decay

A. Levit, D. Nutman, E. Osher, E. Kamhi, R. Navon*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

We have identified three mutations in the β-hexoseaminidase A (HEXA) gene in a juvenile Tay-Sachs disease (TSD) patient, which exhibited a reduced level of HEXA mRNA. Two mutations are novel, c.814G>A (p.Gly272Arg) and c.1305C>T (p.=), located in exon 8 and in exon 11, respectively. The third mutation, c.1195A>G (p.Asn399Asp) in exon 11, has been previously characterized as a common polymorphism in African-Americans. Hex A activity measured in TSD Glial cells, transfected with HEXA cDNA constructs bearing these mutations, was unaltered from the activity level measured in normal HEXA cDNA. Analysis of RT-PCR products revealed three aberrant transcripts in the patient, one where exon 8 was absent, one where exon 11 was absent and a third lacking both exons 10 and 11. All three novel transcripts contain frameshifts resulting in premature termination codons (PTCs). Transfection of mini-gene constructs carrying the c.814G>A and c.1305C>T mutations proved that the two mutations result in exon skipping. mRNAs that harbor a PTC are detected and degraded by the nonsense-mediated mRNA decay (NMD) pathway to prevent synthesis of abnormal proteins. However, although NMD is functional in the patient's fibroblasts, aberrant transcripts are still present. We suggest that the level of correctly spliced transcripts as well as the efficiency in which NMD degrade the PTC-containing transcripts, apparently plays an important role in the phenotype severity of the unique patient and thus should be considered as a potential target for drug therapy.

Original languageEnglish
Pages (from-to)176-183
Number of pages8
JournalMolecular Genetics and Metabolism
Volume100
Issue number2
DOIs
StatePublished - Jun 2010

Keywords

  • Exon skipping
  • Exonic mutation
  • G gangliosidosis
  • HEXA gene
  • Nonsense-mediated mRNA decay (NMD)
  • Premature termination codons (PTCs)
  • Tay-Sachs disease (TSD)
  • β-hexosaminidase (Hex A)

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