Last revised by Rohit Sharma on 21 May 2024

Ataxia-telangiectasia, also known as Louis-Bar syndrome, is a rare multisystem autosomal recessive disorder, sometimes classified as a phakomatosis. It is characterized by multiple telangiectasias, cerebellar ataxia, pulmonary infections, and immunodeficiency. 

On brain imaging, it usually demonstrates vermian atrophy, compensatory enlargement of the fourth ventricle, cerebral infarcts and cerebral hemorrhage secondary to ruptured telangiectatic vessels. 

The estimated incidence is at around 1:40,000-300,000 live births.

The main clinical characteristics include:

  • cerebellar ataxia: progressive and present in all cases

  • oculomucocutaneous telangiectasias

  • movement disorders, e.g. choreoathetosis, myoclonus

  • immunocompromise due to partial combined (humoral and cell-mediated) immunodeficiency 3

  • increased risk of neoplasms

The condition is thought to result from a defective ATM gene, located on chromosome 11q22-23.

In less severe cases, termed "ataxia-telangiectasia variants", there is retention of some ATM kinase activity due to either expression of very low levels of normal ATM protein (from splice site mutations) or expression of mutant ATM (from missense mutations) 4.

Ataxia-telangiectasia variants are a phenotypically heterogeneous group, characterized by slower progression of clinical signs, an extended lifespan compared to most patients with the classical form of the disease with less cellular sensitivity to radiation, susceptibility to malignancies and recurrent sinopulmonary infection.

MRI typically demonstrates cerebellar volume loss and compensatory enlargement of the 4th ventricle. 

Additionally, scattered small white matter T2 hypointensities are often identified in patients with ataxia-telangiectasia, most likely representing tiny hemosiderin deposits related to thrombosis and vascular leaks from telangiectatic vessels 4,5. This imaging appearance can also be seen in amyloid angiopathy, disseminated intravascular coagulopathy and multiple cavernomas 6. “Gliovascular nodules” within the white matter have previously been described and consist of dilated capillary loops with perivascular hemorrhages and hemosiderosis, surrounded by reactive fibrosis and demyelinated white matter 7.

Diffuse T2/FLAIR hyperintense signal within the cerebral white matter consistent with demyelination and gliosis has previously been described in ataxia-telangiectasia and may reflect ischemia and white matter degeneration due to vascular abnormalities 4, severe oligodendrocyte and myelin loss 8, coagulation necrosis 9 and leukodystrophy 10. One study using MR spectroscopy of adult patients with ataxia-telangiectasia suggests that the white matter T2/FLAIR hyperintense signal abnormality is secondary to reduced cellularity rather than active demyelination or ischemia 4.

  • MR spectroscopy: increased choline signal in the cerebellum has been described as a valuable differentiator from other forms of ataxia 2

As there is currently no cure, treatment is generally around supportive measures.

The condition was first described in 1941 by Denise Louis-Bar (1914-1999), a Belgian neuropsychiatrist 11.

See differential for diffuse cerebellar atrophy.

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