Ataxia telangiectasia

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Seyed Arash Javadmoosavi, MD[2] Zaida Obeidat, M.D. For patient information, click here

Ataxia telangiectasia
ICD-10	G11.3
ICD-9	334.8
OMIM	208900
DiseasesDB	1025
MedlinePlus	001394
MeSH	D001260

Ataxia telangiectasia Microchapters
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Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Ataxia telangiectasia from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications and Prognosis
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
CT
MRI
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Treatment
Medical Therapy
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Future or Investigational Therapies
Case Studies
Case #1
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Synonyms and keywords: Louis-bar syndrome, Boder-sedgwick syndrome.

Overview

Ataxia telangiectasia (A-T)is an autosomal recessive disorder caused by mutations in the gene ATM (ataxia-telangiectasia mutated)(11q22.3). This gene is expressed commonly and encodes a protein kinase (ATM kinase) which plays a key role in the control of double-strand-break DNA repair. A-T is a progressive, multisystem disease that has a large number of complex and diverse manifestations that vary with age. The clinical picture of this condition can be very variable and the severity of the pulmonary, immunological and neurological manifestations varies widely between patients and is related to the severity of the underlying mutations and any residual ATM kinase activity. It has been recently suggested that the name A-T should be replaced by ATM syndrome. ATM syndrome represents a neurodegenerative disorder with multisystem involvement due to the absence or reduced levels of ATM protein and kinase activity. The syndrome is characterised by the presence of movement disorders, such as cerebellar ataxia, dystonia, chorea and myoclonus, in association with systemic abnormalities such as immunodeficiency, malignancies, oculocutaneous telangiectasias and an increase in α-fetoprotein levels. The disease most commonly presents with ataxia during the third or fourth year of life. The important first step in the evaluation of young children presenting with ataxia should be α-fetoprotein testing. The diagnosis should then be confirmed by genetic testing to identify the mutations and measure the product of the ATM gene, the protein kinase ATM. This diagnostic test is likely to be available in specialised laboratories only. Patients with A-T die prematurely, the leading causes of death being respiratory diseases and cancer. A minimally estimated annual mortality rate for white patients is 19.5/1000 for ages 15–19 years and reportedly three-fold higher for African-American patients.

Historical Perspective

The term Ataxia-Telangiectasia was initially advanced by Boder and Sedgwick in 1957,in which described eight patients with classical A-T, while in 1958 Centerwall and Miller entitled it Louis-Bar syndrome which relates to Madame Louis-Bar, a Belgian neurologist who published a case report of a 9 year-old boy with cutaneous telangiectasia and progressive cerebellar ataxia. She initially classified this new disease in the group of phacomatosis PPV. In 1993, a case report was published about a 17 year-old boy with cerebellar ataxia concomitant dystonia, myoclonus, pyramidal signs, pulmonary infection, persistent lymphopenia, immunoglobulin deficiency and rising alpha-fetoprotein, termed as ataxia with immune deficiency. In 1995, the responsible gene for A-T(ATM) was identified by Savitsky et al. In 2001, Stewart found a correlation with ATM kinase activity levels in cells and the degree of neurological symptoms in A-T patients.

Classification

• The ataxias can be divided into:
  • Genetic (with or without a family history) and those that are acquired/degenerative.
  • Sporadic ataxia implies there is no family history.
  • Acquired progressive ataxias can be:
    • Immune mediated (paraneoplastic spinocerebellar degeneration, gluten ataxia)
    • Degenerative (cerebellar variant of multiple systems atrophy (type C))
    • Caused by deficiency states (vitamin B12, vitamin E)
    • Toxicity (eg, alcohol-related ataxia, phenytoin)
    • Associated with infections (HIV, sporadic Creutzfeldt-Jakob disease, progressive multifocal leucoencephalopathy).
  • Inherited ataxias can have autosomal dominant, autosomal recessive, X-linked or mitochondrial (maternal) inheritance.
  • Metabolic disorders (Niemann-Pick type C, Tay-Sachs disease).

• There is no established system for the classification of Ataxia Telangiectasia.

Pathophysiology

The responsible gene in AT, ataxia-telangiectasia mutated (ATM), was discovered in 1995 by Savitsky et al., a team led by Yosef Shiloh of Tel Aviv University in Israel. Researchers linked the hyper-sensitivity of AT patients to ionizing radiation (IR) and predisposition to cancer, to "chromosomal instability, abnormalities in genetic recombination, and defective signaling to programmed cell death and several cell cycle checkpoints activated by DNA damage". Earlier observations predicted that the gene altered in AT played a role in DNA damage recognition. These predictions were confirmed when a single gene on chromosome 11 (11q 22-23) was discovered. Since its discovery, the protein product of the ATM gene has been shown to be a part of eukaryotic cell cycle control, DNA repair, and DNA recombination (Lavin, 2004). Specifically, the AT gene serves as a tumor suppressor gene by contributing to a network of genes that link double stranded breaks in DNA to cell cycle arrest and apoptosis (programmed cell death). Patients with ATM have a defective AT gene, which leaves them susceptible to contracting cancer. For example, female ATM patients have a two-fold higher chance of ever having breast cancer, which often occur before the age of 50. ATM patients must try avoiding x-rays at all costs since the radiation induces double-stranded breaks.

Genetics

AT is an autosomal recessive disorder caused by mutations in the ATM gene located on chromosome 11q22-23. It was characterised in June of 1995 and is made up of 66 exons spread across 150kb of genomic DNA. It encodes a 13kb mature transcript with an open reading frame of 9168 nucleotides. The ATM protein is about 370kDa and is ubiquitously expressed and is localised to the cell nucleus. The ATM protein is a large serine-threonine kinase thought to play a role in regulating cell cycle checkpoints, repair of double stranded DNA and meiosis (similar to the BRCA genes). ATM is also known to play a role in regulating p53, BRCA1 and CHEK2. Part of ATM’s role in DNA repair is known to be that of telomere repair as telomeres degrade more rapidly in people affected with AT.

Mutations in the ATM gene are thought to come in two types:

• Null mutations are those which cause complete loss of function of the protein and are therefore inherited in a recessive manner and cause AT.
• ‘Missense’ mutations which produce stable, full sized protein with reduced function e.g. substitutions, short in-frame insertions and deletions etc. These mutations act by dominantly interfering with the normal copy of the protein.

The majority of AT sufferers, 65-70%, have truncating mutations, with exon skipping mutations being particularly common. This results in very low or undetectable levels of ATM protein. Missense mutations are the most common type of mutation found in carriers with breast cancer. Individuals with two missense mutations are believed to have a milder form of AT, which may account for cases of attenuated AT. Therefore it is thought that "subtle constitutional alterations of ATM may impart an increased risk of developing breast cancer and therefore act as a low penetrance, high prevalence gene in the general population" (Maillet et al 2002).

Oculo-cutaneous telangiectasia combined with ataxia are the defining features of the condition. However, some patients with AT, even those with two null mutations who produce no ATM protein at all, may never present with oculo-cutaneous telangiectasia.

Causes

• Ataxia-telangiectasia is inherited, which means it is passed down through families. It is an autosomal recessive trait. This means that both parents must provide a defective gene for the child to have symptoms of the disorder.

• The disease results from defects in the ataxia telangiectasia mutated (ATM) gene. The ATM gene is involved in making protein that control cell division and DNA repair. The ATM protein helps cells to identify damaged and broken DNA and activates enzymes which fix the broken parts.. Defects in this gene can lead to abnormal cell death in various places of the body, including the part of the brain that helps coordinate movement.

• Boys and girls are equally affected.

Differentiating Ataxia telangiectasia from other Diseases

Ataxia telangiectasia like disorder (ATLD) is an extremely rare condition which could be considered as a differential diagnosis to 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 tumors. The gene mutated in ATLD is hMre11 and is located on chromosome 11q21.

Nijmegen breakage syndrome (NBS), also known as ataxia telangiectasia variant 1, is a very rare syndrome which could be considered as a differential diagnosis to AT. People with Nijmegen breakage syndrome show the same immunodeficiency, radiosensitivity and risk of cancer as AT but do not have any ataxia or oculo-cutaneous telangiectasia. Nijmegen breakage syndrome sufferers also show microcephaly. The gene associated with Nijmegen syndrome (Nbs1) is known to be located on 8q21.

Interestingly, the proteins expressed by the hMre11 and Nbs1 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 signaling 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.

In the early ataxic stages children may be diagnosed with cerebral palsy.

Other differential diagnoses are:

• Ataxia oculomotor apraxia type 1
• Ataxia oculomotor apraxia type 2
• Gaucher disease
• Hartnup disease
• Niemann-Pick disease
• Refsum disease

Ataxia telangiectasia must be differentiated from other diseases that cause neurological manifestations in infants.

Diseases	Type of motor abnormality				Clinical findings	Laboratory findings and diagnostic tests	Radiographic findings
	Spasticity	Hypotonia	Ataxia	Dystonia
Leigh syndrome	-	-	+	+	Progressive psychomotor regression Seizures External ophthalmoplegia Lactic acidosis Vomiting	Increased lactate levels in blood and CSF Genetic testing	MRI: abnormal white matter signal in the putamen, basal ganglia, and brainstem on T2 images
Niemann-Pick disease type C	-	-	+	+	Progressive neurodegeneration Hepatosplenomegaly Systemic involvement of liver, spleen, or lung preceedes neurologic symptoms	Abnormal liver function tests Fibroblast cell culture with filipin staining	MRI: Cerebral and cerebellar atrophy Thinning of the corpus callosum
Infantile Refsum disease	-	+	+	-	Abnormalities of the optic nerve and disc Retinitis pigmentosa Sensorineural hearing loss Hepatomegaly and cirrhosis Neurologic deterioration is slower than in Zellweger syndrome or ALD	Elevated plasma VLCFA levels	--
Adrenoleukodystrophy	+	-	-	-	Cognitive and behavioral abnormalities Adrenal insufficiency Hyperpigmented skin Gonadal dysfunction Neurologic deterioration progresses at a variable rate	Elevated plasma VLCFA levels Molecular genetic testing for mutations in the ABCD1 gene	--
Zellweger syndrome	-	+	-	-	Craniofacial dysmorphism Hepatomegaly Neonatal seizures Profound developmental delay MRI findings include cortical and white matter abnormalities Neurologic deterioration is rapid and infants rarely survive beyond six months of age	Elevated plasma VLCFA levels Elevated levels of phytanic acid, pristanic acid, and pipecolic acid in plasma and fibroblasts Reduced plasmalogen in erythrocytes Molecular genetic testing for mutations in the PEX1 or PEX6 genes	--
Pyruvate dehydrogenase deficiency	+	+	+	-	Lactic acidosis Seizures Intellectual disability	Elevated lactate and pyruvate levels in blood and CSF Abnormal PDH enzymatic activity in cultured fibroblasts	--
Arginase deficiency	+	-	-	-	Hyperammonemia Encephalopathy Respiratory alkalosis	Elevated ammonia level Elevated arginine level	--
Holocarboxylase synthetase deficiency	-	+	-	-	Ketoacidosis Dermatitis Alopecia Seizures Developmental delay	Elevated levels of: Beta-hydroxyisovalerate Beta-methylcrotonylglycine Beta-hydroxypropionate Methylcitrate Tiglylglycine	--
Glutaric aciduria type 1	-	-	-	+	Episodes of metabolic decompensation and encephalopathy often precipitated by infection and fever Rarely presents in the newborn period Microencephalic macrocephaly Seizures (approximately 20 percent) Cognitive function is preserved	Elevated levels of: glutaric acid 3-hydroxyglutaric acid	MRI: Frontal and temporal atrophy
Ataxia telangiectasia	-	-	+	-	Progressive cerebellar ataxia Abnormal eye movements Oculocutaneous telangiectasias Immune deficiency Increased risk of malignancy	Elevated serum alpha-fetoprotein level Low IgA and IgG levels Lymphopenia Genetic testing for mutation in the ATM gene	--
Pontocerebellar hypoplasias	-	+	-	-	Progressive muscle atrophy Microcephaly Developmental delay	Genetic testing for PCH gene mutations	MRI : Small cerebellum and brainstem including the pons
Metachromatic leukodystrophy	-	+	+	-	Regression of motor skills Seizures Optic atrophy Reduced or absent deep tendon reflexes Intellectual disability	Deficient arylsulfatase A enzyme activity in leukocytes or cultured skin fibroblasts	--
Pelizaeus-Merzbacher	+	-	+	-	Nystagmus Cognitive impairment Onset in infancy Slowly progressive Language development may be normal	Genetic testing for mutations in PLP1 gene	MRI: White matter abnormalities
Angelman syndrome	-	-	+	-	Profound intellectual disability Postnatal microcephaly Typical abnormal behaviors (paroxysmal laughter, easily excitable)	Methylation studies and chromosome microarray to detect chromosome 15 anomalies and UBE3A mutations	--
Rett syndrome	+	-	-	+	Occurs almost exclusively in females Normal development during first six months followed by regression and loss of milestones Loss of speech capability Stereotypic hand movements Seizures Autistic features	Clinical diagnosis Genetic testing for MECP2 mutations	--
Lesch-Nyhan syndrome	+	-	-	+	Self-mutilating behavior Urinary stones due to hyperuricemia	Elevated uric acid level Abnormal enzymatic activity of HPRT in cultured fibroblasts Genetic testing for HPRT gene mutations	--
Miller-Dieker lissencephaly	+	+	-	-	Lissencephaly Microcephaly Dysmorphic features Seizures Failure to thrive	Cytogenetic testing for 17p13.3 microdeletion	--
Dopa-responsive dystonia	+	-	-	+	Onset in early childhood Symptoms worsen with fatigue and exercise	Positive response to a trial of levodopa	--

Comparison of the clinical features, biomarkers and brain imaging between ataxia telangiectasia (AT), ataxiatelangiectasia-like disorder type 1 (ATLD1) and ataxia telangiectasia-like disorder type 2 (ATLD2)

Clinical Features	AT (ATM)	ATLD1 (MRE11A)	ATLD2 (PCNA)
Ataxia	+	+	+
Dysarthria	+	+	+
Telangiectasia	+	-	+
Eye movement disorders	+	+	-
Photophobia and photosensitivity	-	-	+
Movement disorders (choreoathetosis, dystonia, myoclonus, tremor)	+	+	-
Cognitive dysfunction	+	+	+
Sensorineural hearing loss	-	-	+
Skin abnormalities	+	-	+
Microcephaly	-	-	+
Short stature, developmental delay	+	+	+
Lymphoid tumors predisposition	+	-	Unknown
Recurrent infections	+	-	-
Increased levels of alpha-fetoprotein	+	-	Unknown
Reduced levels of Immunoglobulin	+	-	-
Cerebellar atrophy	+	+	+

AT, ataxia telangiectasia; ATLD1, ataxia telangiectasia-like disorder type 1; ATLD2, ataxia telangiectasia-like disorder type 2.

Epidemiology and Demographics

Epidemiology:

Ataxia-Telangiectasia prevalence is estimated between 1 in 40,000 and 1 in 100,000. Some studies have shown that the prevalence of A-T among adults younger than age 50 is approximately 1 in 500,000. Some mutations are more common than others is certain geographical regions for example, the 7636del9 mutation is a common mutation in European populations which has been shown to increase the risk of breast cancer in carriers.

Etiology:

Ataxia-Telangiectasia is caused by mutations in the ATM (Ataxia Telangiectasia, Mutated) gene which encodes a protein of the same name. The primary role of the ATM protein is coordination of cellular signaling pathways in response to DNA double strand breaks, oxidative stress and other genotoxic stress.

Screening

One of the defective screening test for newborn is severe combined immunodeficiency (SCID), which detect T cells and B cells deficiency or absence from infant dried blood spots. Although there is no modifying therapy or cure for A-T recently, SCID screening test allows for early family education and genetic counseling.
Pre-implantation genetic diagnosis (PGD) can avoid the birth of an affected child. By this screening test, parents who have an affected child (or children) with A-T take its advantages.
Antenatal diagnosis can also be performed using haplotype analysis if a diagnosis has been made for the affected child. In this case, DNA polymorphisms within and around the ATM gene can be utilized even if the pathogenic mutations are not known.

Diagnosis

History and Symptoms | Physical Examination | Laboratory Findings | CT | MRI | Other Diagnostic Studies

Treatment

Medical Therapy | Cost Effectiveness of Therapy | Future or Investigational Therapies

Case Studies

Case #1