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The gene for Machado-Joseph disease maps to the same 3-cM interval as the spinal cerebellar ataxia 3 gene on
G Stevanin1, P S Sousa, G Cancel
1INSERM U289, Hôpital de la Salpêtrière, Paris, France.
Abstract:
Machado-Joseph disease (MJD) is an autosomal dominant neurodegenerative disorder in families of Portuguese-Azorean ancestry. The gene responsible for MJD has been assigned to a 29-cM interval on chromosome 14q. A large Brazilian family with MJD was genotyped with six new microsatellite markers spanning 19 cM on chromosome 14q. Linkage analysis and haplotype reconstruction reduced the MJD candidate region to a 3-cM interval between markers D14S280 and D14S81, permitting positional cloning. This interval also contains the spinal cerebellar ataxia 3 (SCA3) gene, responsible for a genetic subtype of the type I autosomal dominant cerebellar ataxias, clinically related to MJD. This result supports the hypothesis that abnormalities in the same gene may be responsible for both disorders. The minor clinical differences between the two diseases may result from allelic heterogeneity.
Insights
Researchers identified the Machado-Joseph disease (MJD) gene region on chromosome 14q. This finding supports the hypothesis that MJD and spinal cerebellar ataxia 3 (SCA3) may stem from the same gene.
Area of Science:
- Genetics
- Neuroscience
- Molecular Biology
Background:
- Machado-Joseph disease (MJD) is an inherited neurodegenerative disorder affecting individuals of Portuguese-Azorean ancestry.
- The gene responsible for MJD was previously mapped to chromosome 14q.
Purpose of the Study:
- To refine the chromosomal location of the MJD gene.
- To investigate the genetic relationship between MJD and spinal cerebellar ataxia 3 (SCA3).
Main Methods:
- Genotyping a large Brazilian family with MJD using six novel microsatellite markers on chromosome 14q.
- Performing linkage analysis and haplotype reconstruction to narrow down the candidate region.
- Comparing the MJD candidate region with the known location of the SCA3 gene.
Main Results:
- The MJD candidate region was successfully reduced to a 3-cM interval between markers D14S280 and D14S81.
- This refined interval encompasses the gene responsible for spinal cerebellar ataxia 3 (SCA3).
Conclusions:
- The positional cloning of the MJD gene provides a critical step towards understanding its function.
- The findings support the hypothesis that MJD and SCA3 may be caused by mutations in the same gene, with allelic heterogeneity potentially explaining clinical variations.