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| Telomeric chromosome fusions in ataxia telangiectasia indicating the highly recombinogenic nature of chromosome ends that have lost telomeric sequence. The cell in (a) is a t(X;14)(q28,q11) translocation cell from the peripheral T lymphocytes of an A-T patient |
|Western blots showing a loss (lane 2) or a greatly decreased level (lane 11) of ATM in cells from ataxia telangiectasia patients. Loss of the aprataxin protein is seen in patients with ataxia oculomotor apraxia type 1 (lane 9). | |
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Ataxiatelangiectasia |

Identity |

Other names | Louis-Bar syndrome |
Note | see also, in Deep Insight section: Ataxia-Telangiectasia and variants |
Inheritance | autosomal recessive; frequency is about 1 to 2.5/105 newborns; heterozygotes are estimated to be 1% of the general population; founder effect are found in some isolated population |

Clinics |

Note | ataxia telangiectasia is a chromosomeinstability syndrome with cerebellar degeneration, immunodeficiency, and an increased risk of cancers; A-T cells are defective in recognizing double-strand DNA damage to signal for repair |
Phenotype and clinics |  onset of the disease is often noted during the second year of life: there is progressive cerebellar ataxia (initially truncal, with further peripheral extension); ataxia is a constantfeature in this disease; oculomotor apraxia, dysarthria, and dystonia; leading to muscular atrophia  telangiectasia: facial region exposed to sunlight, and eyes (conjunctiva)  combined immunodeficiency (in 70 %): thymus hypoplasia, and IgG2 and 4, IgA, IgE deficiency  other features: growth retardation; hypogonadism; occasionally diabetes mellitus |
Neoplastic risk |  risk of cancers is X100, consisting mainly of T- cell malignancies (a 70-fold and 250-fold increased risks of leukemia and lymphoma respectively) and B-cell malignancies, but not myeloid leukemia; carcinomas of the skin, ovary, breast, and stomach have also been described  cancer treatment is complicated by radiation- and chemo-sensitivity |
Evolution | progressive cerebellar degeneration: patients are usually in awheelchair by the age of ten |
Prognosis |  respiratory infection is the common cause of death, with cancer being the second most common.  survival is often into fourth decade today where optimal medical care is available |

Cytogenetics |

Inborn conditions |  spontaneous chromatid/chromosome breaks, triradials, quadriradials (less prominent phenomenon than in Fanconi anaemia); telomericassociations  the best diagnosis test is on the (pathognomonic) highly elevated level (10% of mitoses) of inv(7)(p14q35), t(14;14)(q11;q32), and other non clonal stable chromosome rearrangements involving 2p12, 7p14, 7q 35, 14q11, 14q32, and 22q11 (illegitimate recombinations between immunoglobulin superfamilly genes Ig and TCR); normal level of those rearrangements are: 1/500 (inv(14)), 1/200(t(7;14)), 1/10 000 (inv(7))  clonal rearrangements further occur in 10% of patients, but without manifestation of malignancy: t(14;14), inv(14), or t(X;14) |
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  | Sporadic (rows 1 and 2) and clonal (row 3) rearrangements in ataxia telangiectasia (R- banding). Row 1, from left to right: inv(7)(p14q35), t(7;7)(p14;q35), t(14;14)(q11;q32), inv(14)(q11q32); Row 2:, from left to right:t(7;14)(p14;q11), t(7;14)(q35;q11), t(7;14)(p14;q32), t(7;14)(q35;q32); Row 3, from left to right: inv(14)(q11;q32), t(X;14)(q28;q11) (note the late replicating X on the left ), t(14;14)(q11;q32) - Courtesy Alain Aurias (modified figure reprinted from Médecine/Sciences 1986; 2: 298-303., by permission of the publisher Masson). |
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Cytogenetics of cancer | clonal rearrangements in T-cell...