Characterization of a partial pseudogene homologous to the adrenoleukodystrophy gene and application to mutation detection.

The gene for the most common peroxisomal disorder, X-linked adrenoleukodystrophy (X-ALD, McKusick #300100), encodes a peroxisomal membrane transporter protein (ALDP), and comprises 10 exons spanning approximately 21 kb. So far, however, the mutation analysis at the genomic level was handicapped by the coamplification, in PCR reactions, of sequences related to the distal exons, also detected by Southern blot hybridization on genomic DNA. We isolated one clone from a human genomic phage library, which represents a partial ALD pseudogene, spanning exon 7 to exon 10 and exhibits approximately 93% sequence homology with the ALD gene in this region. Primers designed in the region of maximum mismatch between the pseudogene and the functional gene allowed the amplification of the functional exons without any contaminating sequences of the pseudogene or other related sequences. This information will greatly facilitate the detection of mutations in distal exons of the ALD gene and increase the reliability of the mutation analysis.