Mutational Analyses on X-Linked Adrenoleukodystrophy Reveal a Novel Cryptic Splicing and Three Missense Mutations in the ABCD1 Gene

Abstract Background X-linked adrenoleukodystrophy is caused by a defective peroxisomal membrane transporter, ABCD1, responsible for transporting very-long-chain fatty acid substrate into peroxisomes for degradation. The main biochemical defect, which is also one of the major diagnostic hallmarks, of X-linked adrenoleukodystrophy is the accumulation of saturated very-long-chain fatty acids in all tissues and body fluids. Methods Direct and reverse-transcribed polymerase chain reactions followed by DNA sequencing-based mutational analyses were performed on one Taiwanese and three Malaysian X-linked adrenoleukodystrophy families. Results A novel splicing donor site mutation (c.1272+1g>a) was identified in a Taiwanese X-linked adrenoleukodystrophy patient, resulting in a deletion of 121 bp and a premature stop codon (p.Val425fs*92) in messenger-RNA transcript. This deletion is caused by the activation of a cryptic splicing donor site in exon 4 of the ABCD1 gene, which is consistent with the prediction by several online algorithms. In addition, three previously described missense mutations (c.965T>C, c.1978C>T, and c.2006A>G), leading to aberrant ABCD1 of p.Leu322Pro, p.Arg660Trp, and p.His669Arg, were also identified in Malaysian probands. Conclusions This is the first report to unveil unequivocally that cryptic splicing-induced aberrant messenger-RNA carrying an internal frameshift deletion results from an intronic mutation in the ABCD1 gene. Furthermore, a polymorphism in intron 9 (c.1992-32c/t; refSNP: rs4898368) of the ABCD1 gene was commonly observed in both Taiwanese and Malaysian populations.