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Trinucleotide repeat expansion, is a DNA mutation that is responsible for causing any type of disorder classified as a trinucleotide repeat disorder. These disorders are progressive and affect the sequences of the human genome, frequently within the nervous system.
The development of the nervous system in humans, or neural development, or neurodevelopment involves the studies of embryology, developmental biology, and neuroscience.These describe the cellular and molecular mechanisms by which the complex nervous system forms in humans, develops during prenatal development, and continues to develop postnatally.
Huntington's disease (HD) is a rare autosomal dominant neurodegenerative disorder caused by mutations in the huntingtin gene (HTT). HD is characterized by loss of medium spiny neurons and astrogliosis. [30] [31] [32] The first brain region to be substantially affected is the striatum, followed by degeneration of the frontal and temporal ...
Many mutations have been associated with loss of expression of the MECP2 gene and have been identified in Rett syndrome patients. These mutations include changes in single DNA base pairs , insertions or deletions of DNA in the MECP2 gene, and changes that affect how the gene information is processed into a protein (RNA splicing). Mutations in ...
Small-scale mutations affect a gene in one or a few nucleotides. (If only a single nucleotide is affected, they are called point mutations.) Small-scale mutations include: Insertions add one or more extra nucleotides into the DNA. They are usually caused by transposable elements, or errors during replication of repeating elements.
Some nonlethal regulatory mutations occur in HOX genes in humans, which can result in a cervical rib [95] or polydactyly, an increase in the number of fingers or toes. [96] When such mutations result in a higher fitness, natural selection favours these phenotypes and the novel trait spreads in the population.
Mutations in this gene lead to tissue overgrowth, or a "hippopotamus"-like phenotype. A fundamental question in developmental biology is how an organ knows to stop growing after reaching a particular size. Organ growth relies on several processes occurring at the cellular level, including cell division and programmed cell death (or apoptosis ...
[50] [51] [52] Mice defective in a gene (Pms2) that ordinarily corrects base mispairs in DNA have about a 100-fold elevated mutation frequency in all tissues, but do not appear to age more rapidly. [53] On the other hand, mice defective in one particular DNA repair pathway show clear premature aging, but do not have elevated mutation. [54]