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Ataxia-telangiectasia (AT) (Boder-Sedgwick syndrome[1] or Louis-Bar syndrome) is a rare, neurodegenerative, inherited disease which affects many parts of the body and causes severe disability. Ataxia refers to poor coordination and telangiectasia to small dilated blood vessels, both of which are hallmarks of the disease.
AT affects the cerebellum (the body’s motor control center) and also weakens the immune system in about 70% of the cases, leading to respiratory disorders and increased risk of cancer. It first appears in early childhood (the toddler stage) with symptoms such as lack of balance, slurred speech, and increased infections. Because all children at this age take time to develop good walking skills, coherent speech, and an effective immune system, it may be some years before AT is properly diagnosed.
So far there appear to be three forms of AT:
These are sometimes classified into ‘types’ from I to IV.
There are several other disorders with similar symptoms that physicians may consider when diagnosing AT. These include:
Ataxia-telangiectasia like disorder (ATLD) is an extremely rare condition which could be considered in the differential diagnosis of AT. ATLD patients are very similar to AT patients in showing a progressive cerebellar ataxia, hypersensitivity to ionising radiation and genomic instability. However, ATLD can be distinguished from AT by the absence of telangiectasias, normal immunoglobulin levels, a later onset of the condition and a slower progression of the disease. It is not known whether ATLD individuals are also predisposed to tumours. The gene mutated in ATLD is hMre11 and is located on chromosome 11q21.
Interestingly, the proteins expressed by the hMre11 (defecting in ATLD) and Nbs1 (defective in NBS) genes exist in the cell as a complex, along with a third protein expressed by the hRad50 gene. This complex, known as the MRN complex, plays an important role in DNA damage repair and signalling and is required to recruit ATM to the sites of DNA double strand breaks. Mre11 and Nbs1 are also targets for phosphorylation by the ATM kinase. Thus, the similarity of the three diseases can be explained in part by the fact that the protein products of the three genes mutated in these disorders interact in common pathways in the cell.
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