Accelerated Aging: Human Progeroid Syndromes
Ataxia telangiectasia is an autosomal recessive disease that occurs in about one in forty thousand to three hundred thousand individuals. Characteristics of this disease appear during infancy and develop during childhood. There is a striking increase in cancer frequency, immunodeficiency, and acute neurodegeneration (particularly of the cerebellum) leading to multiple motor difficulties. Individuals with ataxia telangiectasia die prematurely of cancer or pulmonary disease (probably due to immunodeficiency).
Ataxia telangiectasia is caused by mutations in a large gene (designated ATM) that codes for a protein with phosphorylation (kinase) activity. Cells lacking ATM function are profoundly sensitive to ionizing radiation, have chromosomal instability (including increased telomere shortening), and premature replicative senescence. Research has demonstrated that ATM kinase is involved in regulating cell cycle progression in response to DNA damage by phosphorylating protein targets, particularly the tumor suppressor protein p53 that, in turn, either delays cell cycle progression or initiates programmed cell death. Thus, loss of ATM function results in survival of cells with damaged DNA and/or increased chromosomal breaks following replication of damaged DNA. These outcomes certainly contribute to increased tumorigenesis in ataxia telangiectasia. Notably, individuals with one mutated ATM allele (approximately 1 percent of the population) have a slightly elevated cancer risk, although without the overt phenotype of ataxia telangiectasia.
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