The syndrome of ataxia-telangiectasia is characterized by pathological changes in various systems of the body. Clinically, the central nervous system, eye, skin, upper and lower respiratory tracts, immune system, and viscera are involved.
Central nervous system
- Cerebellar and extrapyramidal systems are the most affected.
- Truncal ataxia is the first presenting symptom of ataxia-telangiectasia and usually appears after the child starts to walk. The first manifestations of truncal ataxia are swaying of the head and trunk on standing and even sitting. The ataxia is progressive and is accompanied by loss of deep tendon reflexes, dystonia, drooling, and dysarthria. Motor function continues to deteriorate, and, by age 10 years, it leads to serious disability, making the use of a wheelchair necessary.
- Mental changes are not detectable in the earlier stages of ataxia-telangiectasia. As the child grows older, deterioration in mental processes occurs with slowing of reactions and lack of responsiveness. Evidence of mental retardation becomes apparent as ataxia-telangiectasia progresses.
- Telangiectasia of the conjunctiva has a later onset than ataxia and usually appears at age 3-7 years. The telangiectasia is first noted in the interpalpebral bulbar conjunctiva away from the limbus. Eventually, the ocular telangiectasia becomes generalized and simulates a conjunctivitis.
- Oculomotor abnormalities appear early in ataxia-telangiectasia and consist of an inability to execute voluntary gaze movements rapidly or on command. Version movements are not restricted, but, on command gaze, they are performed in a halting dyssynergistic fashion. Nystagmus may reduce distance visual acuity and impair fixation. The vestibulo-ocular movements are preserved, but there is a poor ability to initiate saccades. Convergence ability frequently is impaired.
- Visual acuity, pupillary reflex responses, and fundi are normal.
- Cutaneous telangiectasia becomes apparent at age 3-7 years. It is first seen on the ears and palate, across the butterfly area of the face, and the bridge of the nose. As the patient gets older, the telangiectasia extends to the neck, the dorsum of the hands and feet, and in the antecubital and popliteal areas. The telangiectatic vessels originate from the subpapillary venous plexuses.
- Vitiligo and premature graying of the hair have been observed. Other skin manifestations of ataxia-telangiectasia are as follows: seborrheic dermatitis, atopic dermatitis, café au lait spots, scleroderma-like changes, and nummular eczema.
Upper and lower respiratory tracts
- Frequent sinopulmonary infections are common manifestations of ataxia-telangiectasia. The onset of these frequent respiratory infections tends to occur at age 4-6 years.
- Recurrent bronchitis and sinusitis lead to bronchiectasis and pulmonary fibrosis. The recurrent respiratory infections are the cause of death during adolescence or young adulthood even with optimal antimicrobial and supportive treatment.
- A common feature in ataxia-telangiectasia is the deficiency of immunoglobulin A (IgA) associated with normal or elevated levels of immunoglobulin G (IgG) and immunoglobulin M (IgM). Normally, IgA represents approximately 90% of the globulin in nasal secretions and 5% of the serum globulin. Since nasal secretions are associated with antiviral activity and are deficient in ataxia-telangiectasia, there appears to be a causal relationship to the susceptibility for respiratory infection observed in ataxia-telangiectasia.
- Immunological abnormalities in ataxia-telangiectasia include the following: decreased peripheral lymphoid tissue, stunted growth, lymphopenia, absence of delayed hypersensitivity, impaired skin homograft rejection, impaired circulating antibody response to some (weak) antigens, and impaired T-cell function. An elevated alpha-fetoprotein level, present in almost all patients with ataxia-telangiectasia, often is associated with pathologic conditions of the liver and chronic hepatitis.
Viscera: Hypoplasia or atrophy of the thymus gland is a characteristic finding in ataxia-telangiectasia. Ataxia-telangiectasia is associated with glucose intolerance and insulin resistance probably due to defects in the affinity of the receptors for insulin.
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The facies are usually dull, relaxed, and sad, but they are in sharp contrast to the cheerful alert appearance when the child is made to smile.
Hair and skin tend to be coarse and dry. Some gray hair is visible.
Ataxia of stance and gait, greatly diminished tendon reflexes, dysmetria of the arm movements, decreased tone in the arms and legs, and flexor plantar reflexes are present.
Vascular markings of the bulbar conjunctiva, external ears, nasal septum, butterfly of the face, and hard and soft palates are seen.
Tympanic membranes usually are scarred and thickened.
Postnasal drainage and drooling usually are present.
Inspiratory and expiratory rales are present in the lungs.
Testicular or ovarian atrophy is often present.
DNA processing or repair protein is the suspected common denominator in ataxia-telangiectasia.
Ataxia-telangiectasia is inherited as autosomal recessive. Ataxia-telangiectasia is caused by mutations in the ATM (ataxia telangiectasia mutated) gene, which has been localized to band 11q22-23. Each parent is a carrier, meaning that they have 1 normal copy of ATM and 1 copy that is mutated. Ataxia-telangiectasia occurs if a child inherits the mutated ATM gene from each parent, so in a family with 2 carrier parents, there is 1 in 4 chance that a child born to the parents will have ataxia-telangiectasia. 
Ataxia-telangiectasia–like disorder (ATLD) is a rarer disease, caused by a mutation in the hMre11 gene. Patients with ATLD are very similar to those with ataxia-telangiectasia except they do not have telangiectasia, have normal immunoglobulins, and have a slower progression of symptoms. 
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