Defining a metabolic phenotype in the brain of a transgenic mouse model of spinocerebellar ataxia 3.

Many of the spinocerebellar ataxias (SCAs) are caused by expansions of CAG trinucleotide repeats encoding abnormal stretches of polyglutamine. SCA3 or Machado-Joseph disease (MJD) is the commonest dominant inherited ataxia disease, with pathological phenotypes apparent with a CAG triplet repeat length of 61-84. In this study a mouse model of SCA3 has been examined which was produced using a human yeast artificial chromosome containing the MJD gene with a CAG triplet expansion of 84 repeats. These mice have previously been shown to possess a mild progressive cerebellar deficit. NMR-based metabolomics/metabonomics in conjunction with multivariate pattern recognition identified a number of metabolic perturbations in SCA3 mice. These changes included a consistent increase in glutamine concentration in tissue extracts of the cerebellum and cerebrum and spectra obtained from intact tissue using magic angle spinning (1)H-NMR spectroscopy. Furthermore, these profiles demonstrated metabolic abnormalities were present in the cerebrum, a region not previously implicated in SCA3. As well as an increase in glutamine both brain regions demonstrated decreases in GABA, choline, phosphocholine and lactate (representing the summation of lactate in vivo, and postmortem glycolysis of glucose and glycogen). The metabolic changes are discussed in terms of the formation of neuronal intranuclear inclusions associated with SCA3. This study suggests high-resolution (1)H-NMR spectroscopy coupled with pattern recognition may provide a rapid method for assessing the phenotype of animal models of human disease.

Insertion of expanded CAG trinucleotide repeat motifs into a yeast artificial chromosome containing the human Machado-Joseph disease gene.

Machado-Joseph disease or spinocerebellar ataxia 3 (SCA3) is a progressive neurodegenerative disorder caused by pathological expansion of a trinucleotide repeat motif present within exon 4 of the MJD1 gene. Previous attempts to create a transgenic animal model have failed to produce a neurological deficit truly representative of the disease phenotype. This appears to be the result of inappropriate expression of the mutant protein in neuronal populations generally spared in the disease state. Introduction of a human disease gene in the context of a yeast artificial chromosome clone containing endogenous regulatory elements would enhance the potential for correct tissue/cell-specific expression at physiological levels. We report the introduction of expanded CAG repeat motifs into a 250kb yeast artificial chromosome clone spanning the MJD1 locus using two rounds of homologous recombination. Transformants exhibited both expansions and contractions of the motif with alleles ranging in size from 48 to 84 repeat units. The availability of these clones for modelling of the disease in transgenic animals should allow elucidation of the role of repeat length in the phenotypic spectrum of the disease.

Autosomal dominant cerebellar ataxia with dementia: evidence for a fourth disease locus.

The autosomal dominant cerebellar ataxias have proved particularly difficult to classify due to the lack of phenotypic concordance both within and between families. Genetic heterogeneity has been established, and disease loci for spinal cerebellar ataxia have been assigned to chromosomes 6 (SCA1), 12 (SCA2) and 14 (Machado Joseph disease (MJD)). Genetic analysis performed on a large Thai kindred with autosomal dominant cerebellar ataxia, in which frontal lobe signs and dementia are commonly observed in affected family members, exclude linkage to the SCA1, SCA2 and MJD loci. This demonstrates that mutation in at least one further locus can cause spinal cerebellar ataxia, indicating the need for caution in the use of markers for predictive testing or prenatal diagnosis these disorders.