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Ataxia telangiectasia

Clinical signs

Ataxia-telangiectasia (AT) is a hereditary disease that mainly affects the system that corrects spontaneously occurring chromosomal breakage, and as a result DNA damage, in the cells of the body. Clinically it is characterized by cerebellar ataxia, telangiectasias, immune defects, and a predisposition to malignancy.

Patients present in early childhood with progressive cerebellar ataxia and later develop conjunctival telangiectasias, other progressive neurological degeneration, sinopulmonary infection, and malignancies. Telangiectasias typically develop between 3 and 5 years of age. The early stages of the ataxia can be misdiagnosed as ataxic cerebral palsy before the appearance of oculocutaneous telangiectasias. No patient is known to have survived beyond 50 years of age.

AT cells are abnormally sensitive to being killed by ionizing radiation. All the cases up to now have been found to be associated with mutations in the same gene (ATM gene).

Inheritance pattern

Autosomal recessive.

Penetrance

Full

Associated features that can be demonstrated in tests performed during pregnancy

There are no specific ultrasound signs and no associated defects.

What is the risk of recurrence in a subsequent pregnancy?

For a couple who has already had an affected child, the risk is 25% in every subsequent pregnancy.

This also applies to a couple where both partners have been found to carry mutations for Ataxia telangiectasia.

When only one parent carries the abnormal gene, there is no risk that any of their offspring will have the disease;

however, in such families there is a 50% chance that the infant will be a carrier, but he himself will be healthy, like the carrier parent.

The risk for more distant relatives depends on the degree of relationship between the relatives and the affected individuals, the ethnic groups of their partners, the presence of family members with Ataxia telangiectasia in the partners' families, consanguinity between the parents, if present, etc. and is established within genetic counseling.

Molecular genetic information

The gene for the disease

The gene for the various types of Ataxia telangiectasia has been identified and is called ATM

Location

On the long arm of chromosome 11.

Genetic testing

Diagnostic testing

In those ethnic groups in which the common disease-causing gene has been identified, a direct gene mutation screening test can be carried out. For example, in North African Jews, a direct test can be performed to identify the mutation in the ATM gene - C103T - by testing for this mutation alone. See: Testing the disease-causing gene for mutations that are common in a specific ethnic group - autosomal recessive diseases.

Carrier testing

This can be performed only in ethnic groups where there is a known gene/mutation that is responsible for the majority of the affected patients. The disease is common in North African Jews, and the carrier frequency in the healthy North African Jewish population is approximately 1:70. Unlike cystic fibrosis, where there are a number of mutations in the gene that causes the disease, in Ataxia telangiectasia, only one mutation common to most affected individuals and carriers has been found in the North African Jewish population: C103T.

In view of this, it is very important to ascertain the ethnic origins of the couple, and it is advisable to examine (carrier DNA testing) those couples where both partners are fully or even partially of North African Jewish origin.

In Jews of other ethnic groups, carriers cannot be identified.

Carrier status testing in relatives of patients with Ataxia telangiectasia

It is important that relatives of patients with Ataxia telangiectasia clarify which mutations are present in the patient or parents in their family in order to ascertain that they are included in the battery of mutations routinely tested for - otherwise it will be necessary to expand the list of mutations tested for and/or examine the partner. This will be discussed in genetic counseling.

See also: "Introduction to population DNA screening for autosomal recessive diseases such as Cystic fibrosis and others".

Fetal testing

Same as the diagnostic test.

Prenatal diagnosis (amniocentesis) can also be offered to each couple who has had an affected child. The best way is after identifying the mutations in the parents, but if these are not found, indirect linkage analysis can be performed. See: Indirect testing for genetic markers in a family that has one or more patients - when there is only one gene that can cause the disease - autosomal recessive diseases.

Preimplantation diagnosis (before the embryonic cells implant in the uterine wall) can also be offered for this disease - this is performed in special centers, and in special cases this can be considered within genetic counseling.
 
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