The Complete Genomic Sequence of the Machado-Joseph Disease Gene

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Machado-Joseph disease (MJD) is a progressive neurodegenerative disease that is characterized clinically by cerebellar ataxia and various associated symptoms. The disorder is the most common type among the hereditary spinocerebellar ataxias and is inherited with autosomal dominant manner. The causative genetic abnormality is an unstable expansion of the CAG repeat in the MJD gene that maps to chromosome 14q32.1. The genomic structure, expression and physiological function of the gene have been obscure. In this project we determined the complete genomic sequence of MJD to elucidate its genomic structure. We obtained totally 27 cDNA clones by screening four human cDNA libraries, 13 cosmid clones by screening the chromosome 14 specific library and 8 BAC clones by screening RPCI11 human BAC library. A contig of the size of approximately 300kb, including MJD, was constructed by the fiber FISH method. The complete sequence of a BAC clone, B445M7, was determined (175,330bp). The comparison of the genomic, cDNA and EST sequences indicated that the MJD gene spanned 48,240bp, was composed of 11 exons and transcribed at least 5 messengers (approximately 1.4, 1.9, 2.0, 4.8 and 7.0kb) by alternative splicing and polyadenylation. Northern blot analysis confirmed these results and showed the ubiquitous expression of the gene. We found three single nucleotide polymophism (SNP) sites in the coding region ; GT^<527>T/GTC, ^<669>ATG/GTG and TA^<1118>A/TAC.Haplotyping analysis showed that there were only two haplotypes in the Japanese population and the strong linkage disequilibrium was found between the CAG expansion and 527T-669A-987C-1118A haplotype.