Triplet repeat mutation length gains correlate with cell-type specific vulnerability in Huntington disease brain

• Published in: Human molecular genetics Vol. 16; no. 10; pp. 1133 - 1142
• Main Authors: Shelbourne, Peggy F., Keller-McGandy, Christine, Bi, Wenya Linda, Yoon, Song-Ro, Dubeau, Louis, Veitch, Nicola J., Vonsattel, Jean Paul, Wexler, Nancy S., Arnheim, Norman, Augood, Sarah J.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 15.05.2007; Oxford Publishing Limited (England)
• Subjects: Adult; Animals; Base Sequence; Biological and medical sciences; Brain - metabolism; Brain - pathology; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Diseases in Twins - genetics; Diseases in Twins - pathology; DNA Primers - genetics; Female; Fundamental and applied biological sciences. Psychology; Genetics of eukaryotes. Biological and molecular evolution; Genomic Instability; Humans; Huntingtin Protein; Huntington Disease - genetics; Huntington Disease - pathology; Male; Medical sciences; Mice; Mice, Inbred DBA; Mice, Transgenic; Middle Aged; Molecular and cellular biology; Mutation; Nerve Tissue Proteins - genetics; Neurology; Neurons - metabolism; Neurons - pathology; Nuclear Proteins - genetics; Tissue Distribution; Trinucleotide Repeat Expansion; Twins, Monozygotic; Visual Cortex - metabolism; Visual Cortex - pathology; Nervous system diseases; Central nervous system disease; Huntington disease; Genetics; Degenerative disease; Mutation; Extrapyramidal syndrome; Genetic disease; Cerebral disorder
• ISSN: 0964-6906; 1460-2083
• DOI: 10.1093/hmg/ddm054

Huntington disease is caused by the expansion of a CAG repeat encoding an extended glutamine tract in a protein called huntingtin. Here, we provide evidence supporting the hypothesis that somatic increases of mutation length play a role in the progressive nature and cell-selective aspects of HD pathogenesis. Results from micro-dissected tissue and individual laser-dissected cells obtained from human HD cases and knock-in HD mice indicate that the CAG repeat is unstable in all cell types tested although neurons tend to have longer mutation length gains than glia. Mutation length gains occur early in the disease process and continue to accumulate as the disease progresses. In keeping with observed patterns of cell loss, neuronal mutation length gains tend to be more prominent in the striatum than in the cortex of low-grade human HD cases, less so in more advanced cases. Interestingly, neuronal sub-populations of HD mice appear to have different propensities for mutation length gains; in particular, smaller mutation length gains occur in nitric oxide synthase-positive striatal interneurons (a relatively spared cell type in HD) compared with the pan-striatal neuronal population. More generally, the data demonstrate that neuronal changes in HD repeat length can be at least as great, if not greater, than those observed in the germline. The fact that significant CAG repeat length gains occur in non-replicating cells also argues that processes such as inappropriate mismatch repair rather than DNA replication are involved in generating mutation instability in HD brain tissue.