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.

Mutations in the gene for X-linked adrenoleukodystrophy in patients with different clinical phenotypes.

Recently, the gene for the most common peroxisomal disorder, X-linked adrenoleukodystrophy (X-ALD), has been described encoding a peroxisomal membrane transporter protein. We analyzed the entire protein-coding sequence of this gene by reverse-transcription PCR, SSCP, and DNA sequencing in five patients with different clinical expression of X-ALD and in their female relatives; these clinical expressions were cerebral childhood ALD, adrenomyeloneuropathy (AMN), and "Addison disease only" (ADO) phenotype. In the three patients exhibiting the classical picture of severe childhood ALD we identified in the 5' portion of the X-ALD gene a 38-bp deletion that causes a frameshift mutation, a 3-bp deletion leading to a deletion of an amino acid in the ATP-binding domain of the ALD protein, and a missense mutation. In the patient with the clinical phenotype of AMN, a nonsense mutation in codon 212, along with a second site mutation at codon 178, was observed. Analysis of the patient with the ADO phenotype revealed a further missense mutation at a highly conserved position in the ALDP/PMP70 comparison. The disruptive nature of two mutations (i.e., the frameshift and the nonsense mutation) in patients with biochemically proved childhood ALD and AMN further strongly supports the hypothesis that alterations in this gene play a crucial role in the pathogenesis of X-ALD. Since the current biochemical techniques for X-ALD carrier detection in affected families lack sufficient reliability, our procedure described for systematic mutation scanning is also capable of improving genetic counseling and prenatal diagnosis.

Population study of a sequence polymorphism in intron 2 of the human beta-globin gene.

The distribution of a nucleotide polymorphism in intron 2 of the beta-globin gene (IVS-2 nt 666 C > T was examined in populations in southern Germany and Cameroon. The allelic frequencies were 0.86 for T and 0.14 for C in southern Germany and 0.87 for T and 0.13 for C in Cameroon, respectively.