DNA repair defects are seen in nearly all of the diseases described as accelerated aging disease, in which various tissues, organs or systems of the human body age prematurely. Because the accelerated aging diseases display different aspects of aging, but never every aspect, they are often called segmental progerias by biogerontologists.[citation needed]
deletion of ATR in adult mice leads to a number of disorders including hair loss and graying, kyphosis, osteoporosis, premature involution of the thymus, fibrosis of the heart and kidney and decreased spermatogenesis[2]
deficient transcription coupled NER with time-dependent accumulation of transcription-blocking damages;[7] mouse life span reduced from 2.5 years to 5 months;[8]) Ercc1−/− mice are leukopenic and thrombocytopenic, and there is extensive adipose transformation of the bone marrow, hallmark features of normal aging in mice[6]
some mutations in ERCC2 cause Cockayne syndrome in which patients have segmental progeria with reduced stature, intellectual disability, cachexia (loss of subcutaneous fat tissue), sensorineural deafness, retinal degeneration, and calcification of the central nervous system; other mutations in ERCC2 cause trichothiodystrophy in which patients have segmental progeria with brittle hair, short stature, progressive cognitive impairment and abnormal face shape; still other mutations in ERCC2 cause xeroderma pigmentosum (without a progeroid syndrome) and with extreme sun-mediated skin cancer predisposition[9]
mutations in ERCC4 cause symptoms of accelerated aging that affect the neurologic, hepatobiliary, musculoskeletal, and hematopoietic systems, and cause an old, wizened appearance, loss of subcutaneous fat, liver dysfunction, vision and hearing loss, chronic kidney disease, muscle wasting, osteopenia, kyphosis and cerebral atrophy[6]
mice with deficient ERCC5 show loss of subcutaneous fat, kyphosis, osteoporosis, retinal photoreceptor loss, liver aging, extensive neurodegeneration, and a short lifespan of 4–5 months
premature aging features with shorter life span and photosensitivity,[14] deficient transcription coupled NER with accumulation of unrepaired DNA damages,[15] also defective repair of oxidatively generated DNA damages including 8-oxoguanine, 5-hydroxycytosine and cyclopurines[15]
premature aging features with shorter life span and photosensitivity,[14] deficient transcription coupled NER with accumulation of unrepaired DNA damages,[15] also defective repair of oxidatively generated DNA damages including 8-oxoguanine, 5-hydroxycytosine and cyclopurines[15]
deficiency causes trichothiodystrophy (TTD) a premature-ageing and neuroectodermal disease; humans with GTF2H5 mutations have a partially inactivated protein[16] with retarded repair of 6-4-photoproducts[17]
SIRT6-deficient mice develop profound lymphopenia, loss of subcutaneous fat and lordokyphosis, and these defects overlap with aging-associated degenerative processes[26]
mice defective in SIRT7 show phenotypic and molecular signs of accelerated aging such as premature pronounced curvature of the spine, reduced life span, and reduced non-homologous end joining[27]
lack of Zmpste24 prevents lamin A formation and causes progeroid phenotypes in mice and humans, increased DNA damage and chromosome aberrations, sensitivity to DNA-damaging agents and deficiency in homologous recombination[36]
DNA repair defects distinguished from "accelerated aging"
Most of the DNA repair deficiency diseases show varying degrees of "accelerated aging" or cancer (often some of both).[37] But elimination of any gene essential for base excision repair kills the embryo—it is too lethal to display symptoms (much less symptoms of cancer or "accelerated aging").[38]
Rothmund-Thomson syndrome and xeroderma pigmentosum display symptoms dominated by vulnerability to cancer, whereas progeria and Werner syndrome show the most features of "accelerated aging". Hereditary nonpolyposis colorectal cancer (HNPCC) is very often caused by a defective MSH2 gene leading to defective mismatch repair, but displays no symptoms of "accelerated aging".[39] On the other hand, Cockayne Syndrome and trichothiodystrophy show mainly features of accelerated aging, but apparently without an increased risk of cancer[40] Some DNA repair defects manifest as neurodegeneration rather than as cancer or "accelerated aging".[41] (Also see the "DNA damage theory of aging" for a discussion of the evidence that DNA damage is the primary underlying cause of aging.)
Debate concerning "accelerated aging"
Some biogerontologists question that such a thing as "accelerated aging" actually exists, at least partly on the grounds that all of the so-called accelerated aging diseases are segmental progerias. Many disease conditions such as diabetes, high blood pressure, etc., are associated with increased mortality. Without reliable biomarkers of aging it is hard to support the claim that a disease condition represents more than accelerated mortality.[42]
Against this position other biogerontologists argue that premature aging phenotypes are identifiable symptoms associated with mechanisms of molecular damage.[37] The fact that these phenotypes are widely recognized justifies classification of the relevant diseases as "accelerated aging".[43] Such conditions, it is argued, are readily distinguishable from genetic diseases associated with increased mortality, but not associated with an aging phenotype, such as cystic fibrosis and sickle cell anemia. It is further argued that segmental aging phenotype is a natural part of aging insofar as genetic variation leads to some people being more disposed than others to aging-associated diseases such as cancer and Alzheimer's disease.[44]
DNA repair defects and increased cancer risk
Individuals with an inherited impairment in DNA repair capability are often at increased risk of cancer.[45] When a mutation is present in a DNA repair gene, the repair gene will either not be expressed or be expressed in an altered form. Then the repair function will likely be deficient, and, as a consequence, damages will tend to accumulate. Such DNA damages can cause errors during DNA synthesis leading to mutations, some of which may give rise to cancer. Germ-line DNA repair mutations that increase the risk of cancer are listed in the Table.
^Weinfeld M, Xing JZ, Lee J, Leadon SA, Cooper PK, Le XC (2001). "Factors influencing the removal of thymine glycol from DNA in γ-irradiated human cells". Factors influencing the removal of thymine glycol from DNA in gamma-irradiated human cells. Progress in Nucleic Acid Research and Molecular Biology. Vol. 68. pp. 139–49. doi:10.1016/S0079-6603(01)68096-6. ISBN9780125400688. PMID11554293. {{cite book}}: |journal= ignored (help)
^ abcdD'Errico M, Pascucci B, Iorio E, Van Houten B, Dogliotti E (2013). "The role of CSA and CSB protein in the oxidative stress response". Mech. Ageing Dev. 134 (5–6): 261–9. doi:10.1016/j.mad.2013.03.006. PMID23562424. S2CID25146054.
^Gonzalo S, Kreienkamp R (2016). "Methods to Monitor DNA Repair Defects and Genomic Instability in the Context of a Disrupted Nuclear Lamina". The Nuclear Envelope. Methods in Molecular Biology. Vol. 1411. pp. 419–37. doi:10.1007/978-1-4939-3530-7_26. ISBN978-1-4939-3528-4. PMC5044759. PMID27147057.
^Bernstein C, Bernstein H, Payne CM, Garewal H. DNA repair/pro-apoptotic dual-role proteins in five major DNA repair pathways: fail-safe protection against carcinogenesis. Mutat Res. 2002 Jun;511(2):145-78. Review.
^Viktorsson K, De Petris L, Lewensohn R (2005). "The role of p53 in treatment responses of lung cancer". Biochem. Biophys. Res. Commun. 331 (3): 868–80. doi:10.1016/j.bbrc.2005.03.192. PMID15865943.