Molecular genetical approach for multifactorial neuropsychiatric diseases

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Chorea-acanthocytosis (ChAc) is a human hereditary neurodegenerative disorder with autosomal recessive transmission, in which selective degeneration of striatum has been reported in brain pathology. Clinically, ChAc shows Huntington's disease-like neuropsychiatric symptoms and red blood cell acanthocytosis, and much variation in symptoms are observed even in brother cases. Recently, we identified the gene, CHAC (VPS13A) encoding a protein named chorein in which a deletion mutation was found in Japanese ChAc families. Then we identified the mouse CHAC cDNA sequence and the exon-intron structures of the gene, and produced a ChAc-model mouse introducing #60-61 exons-deletion corresponding to a human disease mutation by gene-targeting technique. The mice began to show acanthocytosis and motor disturbance after becoming old age. In behavioral observations, locomotor activity was significantly decreased, and the contact time at social interaction test was decreased significantly in the model mice. In the brain pathology, many apoptotic cells were observed in the striatum of the mutant mice. In neurochemical determination, dopamine-metabolite, HVA concentration decreased significantly in the portion including midbrain of the mutant mice. These findings are well consistent with the human results reported elsewhere and indicate that the ChAc-model mice showed mild phenotype with late adult onset. The ChAc-model mouse therefore provides a good model system to study the human disease. The mice are produced as hybrid of 129 and C57BI/B6, and there are much variations in the degree of degeneration in the sriatum and other phenotypes, which might suggest the existence of modifier genes. Then we produced the ChAc-model mouse with three kinds of strains-background, C57BL/6J, BALB/cbyJ, and DBA/2J. Only DBA/2J ChAc-model mice showed reduced body weight from 3 months after birth.