α-Tocopherol transfer protein gene: Exon skipping of all transcripts causes ataxia

This report concerns the characterization of the alpha-tocopherol transfer protein (alpha-TTP) gene in a Japanese family affected by ataxia with isolated vitamin E deficiency (AVED). The sequence analysis revealed a G-to-A transition at the 3' end of exon 3 in both alleles, which predicts outsplicing of this exon from premessenger RNA and the concomitant frame shift in the ataxic patient. We used reverse transcriptase-polymerase chain reaction to analyze alpha-TTP gene transcripts. All transcripts in peripheral blood lymphocytes of the AVED patient, who was treated with large doses of vitamin E, lacked exon 3. The deduced truncated protein shares only 43% of the normal alpha-TTP. Normal control tissues and cells contained normal transcripts and, unexpectedly, also the same mutant; transcripts as those of the patient, although with different transcription levels. Treatment of normal fibroblasts with clinically relevant concentrations of vitamin E increased production of transcripts in a dose-dependent manner. We propose that exon skipping of all transcripts through the complete inactivation of the splice site accounts for the clinical onset of AVED and for the clinical resistance to vitamin E in our patient.