NOVEL MUTATIONS IN THE ABCD1 GENE OF TWO TAIWANESE PATIENTS WITH ADRENOLEUKODYSTROPHY

Objectives: The childhood cerebral form of X-linked adrenoleukodystrophy (X-ALD) is a severe metabolic disease without a definite effective therapy except for hematopoietic stem cell transplantation in the appropriate disease stage. Mutations in the ABCD1 gene have been identified in the majority of X-ALD patients and almost 60% of mutations are nonrecurrent. Thus, identification of the mutation affecting the new family is necessary, especially for carrier diagnosis and genetic counseling. Two Taiwanese children with XALD were analyzed for mutations in the X-ALD gene (ABCD1).

Methods: Fibroblast Cultures. Fibroblasts were grown from skin biopsy specimens according to established procedures described in detail previously (19). Mutation Analysis ABCD1 mutation analysis in the patients was performed at the cDNA level. Total RNA was isolated from primary skin fibroblasts using RNeasy mini kit (Qiagen), cDNA was then prepared using Superscript II reverse transcriptase (Invitrogen). PCR strategy and primers used for amplifying ABCD1 gene are shown in Figure 1. The entire cDNA of the ABCD1 gene were covered by three PCR amplicons and used for direct DNA sequencing.

Results: In this study we analyzed two ALD patients, who had typical abnormalities in plasma (elevated levels of VLCFAs) and brain image. Sequence analysis of the ABCD1 gene of these patients revealed 2 novel mutations. The mutations involve an in-frame trinucleotide deletion and a point mutation. Patient 1 has a trinucleotide deletion (1624–1626 del CAT) in the exon 6 leading to deletion of a single amino acid at position 542. Patient 2 has a point mutation (1520 G>A) in exon 6 converting the glycine at position 507 to an aspartic acid.

Conclusion: Two novel mutations were identified. There was an in-frame trinucleotide deletion (1624 del CAT) in one child, and a G>A (G507A) point mutation in the other. Both mutations were located at exon 6, which may be the hot exon in Chinese population. Both mutations in exon 6 cause the changes in the intracellular domain of ALDP and may lead to instability or loss of function of ALDP resulting in accumulation of VLFCAs. Further investigation of ALDP stability in these two patients is needed to clarify the impact of these ABCD1 mutations.