Ataxia Telangiectasia

Slide 1 · ATAXIA–TELANGIECTASIA

A multisystem disorder of DNA-damage signaling, neurodegeneration and immune dysfunction

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · One inherited defect, four disease domains

Neurological

Early ataxic–dyskinetic syndrome; Progressive deficits

Vascular

Conjunctival and cutaneous telangiectasias

Immune

Variable B- and T-cell abnormalities; Infections

Neoplastic

Elevated risk of leukemias and lymphomas

ATM loss of function

Slide 3 · Disease classification begins with inheritance

Autosomal recessive

Disease requires pathogenic alterations of both ATM copies.

Childhood-onset multisystem phenotype.

Spinocerebellar degeneration

Part of the inherited ataxia spectrum.

Neurological manifestations coexist with systemic abnormalities.

Slide 4 · Characteristic clinical presentation evolves with age

Early childhood

Unsteady walking and an ataxic–dyskinetic syndrome

Often early

Recurrent sinopulmonary bacterial infections

Subsequently

Conjunctival and skin telangiectasias

Later evolution

Dysarthria and eye-movement abnormalities

Slide 5 · ATM links genome maintenance to systemic disease

Inherited ATM defects

Loss of normal ATM-mediated signaling

Abnormal double-strand-break response

Defective checkpoint and repair coordination

Tissue-specific consequences

Neurodegeneration, immune dysfunction, cancer predisposition

Slide 6 · ATM is encoded on chromosome 11

11q22–q23

The ATM gene encodes a protein kinase.

ATM as a central organizer of responses to DNA double-strand breaks.

Ataxia–telangiectasia is caused by inherited ATM defects.

Slide 7 · ATM is a signaling kinase, not merely a repair enzyme

Principal molecular role

Recognizes/coordinates the cellular response to DNA double-strand breaks.

Relays damage signals to downstream effectors.

Important distinction

ATM deficiency disrupts a response network.

Avoid equating ATM with a single DNA-joining reaction.

Slide 8 · Double-strand breaks require coordinated responses

DNA double-strand break

Both strands of the DNA duplex are injured

ATM-dependent signaling

Damage signal is relayed to effector pathways

Cellular decision

Checkpoint control, repair response or apoptosis

Slide 9 · ATM activates the p53 axis after DNA damage

DNA damage

Double-strand break

ATM kinase

Phosphorylation signaling

P53 pathway

Stabilized/activated p53

Cell fate

Arrest, senescence or apoptosis

Slide 10 · Damage signaling normally restrains cell proliferation

Cell-cycle checkpoint

Provides time to respond to damaged DNA.

Limits propagation of genomic lesions.

Programmed cell death

Removes severely damaged cells.

Part of the ATM → p53 response network.

Slide 11 · P53 acts downstream of ATM as a tumor suppressor

DNA damage

ATM and related stress signals

P53 response

Damage-associated transcriptional programs

Tumor prevention

Cell-cycle arrest, senescence or apoptosis

Slide 12 · DNA damage can lead to distinct cellular outcomes

Temporary arrest

Pause cell-cycle progression

Senescence

Durable withdrawal from division

Apoptosis

Eliminate the injured cell

Context dependent

The outcome depends on cellular stress and signaling

Activated p53

Slide 13 · ATM signaling extends beyond canonical DNA repair

Telomere maintenance

Genome-end homeostasis

Mitochondria

Mitochondrial homeostasis

Oxidative stress

Stress-response regulation

Proteostasis

Ubiquitin–proteasomal degradation

ATM signaling

Slide 14 · Defective genome surveillance causes chromosomal instability

ATM deficiency

Impaired response to double-strand breaks

Persistence of damage

Genomic instability can accumulate

Pathological impact

Predisposition to malignant transformation

Slide 15 · Radiation hypersensitivity reflects defective break repair

DNA double-strand breaks

Robbins explicitly links ATM deficiency to radiation hypersensitivity.

The relevant mechanism is inadequate repair of radiation-associated double-strand DNA injury.

Radiosensitivity belongs to the molecular phenotype, even though it is not the presenting neurological feature.

Slide 16 · Cerebellar degeneration is a central tissue phenotype

Neurological localization

Neurodegeneration particularly affects the cerebellum.

This explains prominence of ataxia in the syndrome.

Limits of present source

The relevant Robbins excerpt does not detail a diagnostic histological pattern.

A cellular pathogenesis beyond ATM loss is not established there.

Slide 17 · The mechanism of neuronal death is not settled

Mechanistic uncertainty

ATM influences apoptosis, telomeres, mitochondria, oxidative stress and proteostasis.

Robbins does not identify which dysfunction(s) cause the neuronal degenerative phenotype.

The existence of plausible pathways is not proof that any one is dominant.

Slide 18 · Single-strand repair disorders offer a mechanistic parallel

Ataxia–telangiectasia

Defective double-strand-break response associated with cerebellar neurodegeneration.

Other inherited ataxias

Comparable neurodegeneration when single-strand-break repair is disrupted.

Slide 19 · DNA maintenance matters in postmitotic neurons

Established by Robbins

Loss of ATM is associated with progressive neuronal dysfunction and degeneration.

Not established by the excerpt

The relative contributions of oxidative stress, mitochondria, telomeres and proteostasis to neuronal loss.

Slide 20 · Different tissues produce different clinical consequences

Tissue / system

Relevant ATM-linked process

Recognized consequence

Cerebellum / CNS

DNA-damage response; Other ATM-regulated functions

Ataxia and neurological decline

Lymphocyte lineages

Recombination and antibody maturation

Immune dysfunction

Dividing tissues

Genome surveillance and p53 response

Cancer predisposition

Slide 21 · Ataxia is an early neurological clue

Unsteadiness in walking

Gait abnormality commonly appears early in childhood.

The disorder is described as an ataxic–dyskinetic syndrome.

Early neurological symptoms can precede later visible telangiectasias.

Slide 22 · Ataxia and dyskinesia are distinct components

Ataxia

Impaired coordination and stability.

Clinically evident as an unsteady gait.

Dyskinesia

Abnormal involuntary movement component.

Part of the syndrome.

Slide 23 · Speech changes emerge as degeneration progresses

Dysarthria

Speech becomes dysarthric later in the clinical course.

Dysarthria is a neurological manifestation rather than a primary language disorder.

Its emergence adds evidence of progressive motor-system involvement.

Slide 24 · Eye-movement abnormalities join the later phenotype

Oculomotor dysfunction

Eye-movement abnormalities develop during progression.

These are distinct from the visible conjunctival telangiectasias.

The combination of gait, speech and eye findings supports a neurological syndrome.

Slide 25 · Neurological progression is sustained, not episodic

Onset

Early childhood unsteadiness

Evolution

An ataxic–dyskinetic syndrome

Further progression

Dysarthria and eye-movement problems

Long-term course

Relentless neurological decline

Slide 26 · Telangiectasias are characteristic vascular findings

Conjunctival lesions

Visible dilated surface vessels are a recognized feature.

They often arise after neurological onset.

Cutaneous lesions

Telangiectasias also develop in the skin.

Vascular findings coexist with, rather than explain, the ataxia.

Slide 27 · Vascular and neurological eye findings should not be conflated

Conjunctival telangiectasia

Superficial vascular abnormality.

A characteristic systemic sign.

Abnormal eye movements

Motor-system dysfunction.

Reflects progressive neurological involvement.

Slide 28 · An early neurological case: Localize and integrate

Clinical vignette

A young child develops progressive unsteadiness in walking. Recurrent respiratory infections are also reported, but no skin vascular lesions are yet evident.

Reasoning question

Which disease mechanism can plausibly unify neurological and immunological abnormalities?

Slide 29 · The absence of early telangiectasia is not exclusionary

Chronological fact

Early ataxic–dyskinetic symptoms with later conjunctival and skin telangiectasias.

Clinical reasoning implication

Do not require all hallmark domains to appear simultaneously in early childhood.

Slide 30 · Neurological findings anchor the CNS differential

Feature

Ataxia–telangiectasia

Interpretive role

Onset

Early childhood

Raises suspicion of inherited disease

Movement

Ataxic–dyskinetic syndrome

Multicomponent motor phenotype

Progression

Dysarthria and abnormal eye movements

Evolving neurological deficit

Systemic clues

Telangiectasias and immunodeficiency

Distinguishes it from isolated cerebellar syndromes

Slide 31 · The immune deficit affects adaptive immunity

B-cell-related abnormalities

Defective production of selected isotype-switched antibodies.

May include reduced IgA and IgG2 production.

T-cell-related abnormalities

Variable defects in cellular immunity.

Associated with thymic hypoplasia.

Slide 32 · Immune severity varies among affected individuals

Variable B- and T-cell dysfunction

Immune defects of variable severity.

Both humoral and cellular immunity may be affected.

T-cell dysfunction is often less pronounced than humoral abnormalities.

Slide 33 · Failure of antibody isotype switching is prominent

B-cell response

Antigen-specific humoral response

Ig class switching

DNA recombination changes the antibody isotype

ATM deficiency

Switching-related DNA damage is poorly handled

Humoral phenotype

Defective IgA and IgG2 production

Slide 34 · IgA deficiency is part of the characteristic profile

Impaired IgA production

IgA is specifically identified among impaired switched isotypes.

The problem is a humoral immune defect within a broader ATM syndrome.

Do not mistake this multisystem disorder for an isolated antibody deficiency.

Slide 35 · IgG2 deficiency provides an additional humoral clue

Impaired IgG2 production

IgG2 among the prominent switched-antibody defects.

The abnormality is consistent with defective recombination during isotype switching.

The humoral phenotype does not imply that all immunoglobulin classes are uniformly absent.

Slide 36 · Thymic hypoplasia accompanies T-cell dysfunction

ATM deficiency

Broad effects on lymphocyte biology

Thymic hypoplasia

Associated with T-cell abnormalities

Cellular immunity

Defects are generally less marked than humoral defects

Slide 37 · Antigen-receptor assembly requires controlled DNA breaks

V(D)J recombination

Rearrangement of antigen-receptor gene segments

Double-strand-break intermediates

DNA ends require controlled stabilization

ATM-dependent contribution

Stability of break complexes during recombination

Possible consequence

Impaired receptor generation

Slide 38 · Class switching and V(D)J recombination are not identical

V(D)J recombination

Builds antigen-receptor gene diversity.

ATM helps maintain double-strand break complexes.

Isotype switching

Changes antibody constant-region class.

ATM-associated repair defects can disturb this DNA recombination process.

Slide 39 · ATM links DNA repair to lymphocyte maturation

DNA-level process

Programmed recombination produces DNA intermediates that require controlled handling.

Clinical consequence

Impaired receptor formation and switching contribute to immune incompetence.

Slide 40 · Sinopulmonary bacterial infections are common

Immunodeficiency

Variable defects in antibody and T-cell compartments

Clinical infection pattern

Recurrent upper and lower respiratory bacterial infections

Presentation

Infections may accompany early unsteady gait

Slide 41 · Autoimmune manifestations can coexist with infection

Dysregulated immunity

Multiple autoimmune phenomena in affected patients.

Immune dysfunction is not confined to insufficient antimicrobial defense.

The combination underscores disordered immune regulation.

Slide 42 · The respiratory and neurological axes are independent clues

Recurrent respiratory infection

Prominent clinical consequence of adaptive immune defects.

Progressive gait ataxia

Consequence of neurodegeneration affecting the cerebellum.

Slide 43 · ATM deficiency increases lymphoid cancer susceptibility

Genome instability

Defective responses to DNA breaks

Lymphoid vulnerability

Antigen-receptor gene recombination involves DNA breaks

Neoplastic risk

Increased leukemia and lymphoma incidence

Slide 44 · T-cell leukemia is a highlighted malignancy

Lymphoid neoplasia

Robbins Chapter 28 emphasizes that many patients develop lymphoid neoplasms.

T-cell leukemias are particularly noted in the neurological chapter.

Chapter 7 also identifies a marked increase in lymphomas.

Slide 45 · Cancer predisposition and immunodeficiency share a genomic basis

V(D)J recombination

May compromise antigen-receptor generation

Isotype switching

May compromise switched antibody output

Damage checkpoints

Can fail to suppress damaged cells

Clinical endpoint

Immune deficiency and increased malignancy risk

ATM-dependent DNA-break response

Slide 46 · Germline ATM disease differs from somatic ATM mutation

Germline ATM defects

Inherited autosomal recessive syndrome.

Neurological, immune, vascular and cancer phenotype.

Somatic ATM driver mutations

Acquired variants within tumor clones.

Reported in certain lymphoid neoplasms; Not equivalent to inherited syndrome.

Slide 47 · A second clinical case: Expanding phenotype

Clinical vignette

A patient with childhood-onset ataxia and conjunctival telangiectasias has recurrent bacterial respiratory infections. Later, a lymphoid malignancy is identified.

Reasoning question

Which cellular defect connects antibody dysfunction with cancer susceptibility?

Slide 48 · Friedreich ataxia differs in its molecular mechanism

Characteristic

Ataxia–telangiectasia

Friedreich ataxia

Gene

ATM

FXN

Molecular lesion

DNA-break response kinase defect

GAA repeat expansion with reduced frataxin

Characteristic systemic clue

Immunodeficiency; Telangiectasias

Cardiomyopathy; Sensory neuropathy

Shared phenotype

Progressive ataxia

Progressive ataxia

Slide 49 · Dominant spinocerebellar ataxias have different genetic patterns

Ataxia–telangiectasia

Autosomal recessive ATM disease.

Systemic immune and vascular manifestations.

Spinocerebellar ataxias

Often autosomal dominant.

May involve CAG/polyglutamine, noncoding-repeat or conventional mutations.

Slide 50 · Bloom syndrome and ATM disease share instability, not phenotype

Feature

Ataxia–telangiectasia

Bloom syndrome

Inheritance

Autosomal recessive

Autosomal recessive

Defective factor

ATM kinase response

Homologous-recombination helicase

Neuroimmune phenotype

Ataxia and immunodeficiency emphasized

Developmental anomalies emphasized

Cancer risk

Increased

Increased

Slide 51 · Fanconi anemia is another repair-defect cancer syndrome

Feature

Ataxia–telangiectasia

Fanconi anemia

Principal issue

Double-strand DNA break signaling

DNA cross-link repair pathway

Dominant clinical axis

Ataxia plus immune dysfunction

Developmental changes; Bone marrow failure

DNA-damage sensitivity

Radiation hypersensitivity

Cross-linking chemotherapy hypersensitivity

Cancer predisposition

Leukemia / lymphoma

Leukemia

Slide 52 · X-linked hyper-IgM and ATM disease share a switching defect

Ataxia–telangiectasia

ATM-dependent DNA repair and recombination defect.

Immune phenotype occurs with ataxia, telangiectasias and cancer susceptibility.

X-linked hyper-IgM

Defective CD40L-related T–B interaction impairs isotype switching.

No ATM-based neurodegenerative syndrome is implied.

Slide 53 · Use phenotype and mechanism together in the differential

Candidate disorder

Discriminating mechanism

Anchor phenotype

Ataxia–telangiectasia

ATM / double-strand-break response

Ataxia + telangiectasia + immunity defect

Friedreich ataxia

FXN / frataxin deficiency

Ataxia + cardiomyopathy

Autosomal dominant SCA

Repeat or other dominant variants

Inherited cerebellar syndrome

Fanconi anemia

DNA cross-link pathway

Marrow failure / developmental anomalies

Slide 54 · Neurological findings alone do not capture disease burden

Motor

Gait, speech and ocular motor changes

Vascular

Conjunctival and skin findings

Immune

Respiratory infection pattern and humoral defects

Oncology

Awareness of lymphoid neoplasia

Full clinical assessment

Slide 55 · The disorder is progressive and life-limiting

Long-term clinical course

Relentless progression of neurological disease.

Death is reported as typically occurring in early adulthood.

Clinical burden includes recurrent infections and lymphoid malignancy, in addition to neurological deterioration.

Slide 56 · Ataxia–telangiectasia exemplifies pleiotropy

One disease gene

Biallelic ATM dysfunction

Shared cellular process

Defective double-strand-break response

Different tissue contexts

Neurons, lymphocytes and proliferating tissues

Distinct phenotypes

Neurodegeneration, immunodeficiency, cancer

Slide 57 · A pathogenesis question: What remains unresolved?

Clinical vignette

A researcher proposes that mitochondrial dysfunction is the unique proven cause of neuronal degeneration in ataxia–telangiectasia.

Reasoning question

How should this statement be evaluated against Robbins?

Slide 58 · Pathology synthesis: A four-part causal map

ATM kinase defect

Inherited dysfunction

DNA damage / recombination

Abnormal checkpoint and repair response

Immune + proliferative tissues

Infections and malignancy risk

Nervous system

Progressive cerebellar dysfunction

Slide 59 · Five findings to retain

Early-onset, progressive ataxic–dyskinetic syndrome.

Later conjunctival and cutaneous telangiectasias.

Variable B- and T-cell immunodeficiency; IgA and IgG2 defects are prominent.

ATM orchestrates responses to DNA double-strand breaks.

Radiation sensitivity and lymphoid malignancy risk reflect genome-maintenance failure.

Slide 60 · Primary textbook references

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th ed. (2026). Chapter 28: The Central Nervous System; Spinocerebellar Degenerations—Ataxia-Telangiectasia (pp. 1171–1172).

Same textbook, Chapter 7: Primary (Inherited) Immunodeficiencies—Ataxia Telangiectasia; p53 signaling; Homologous Recombination Repair Factors.

Same textbook, Chapter 1: DNA Damage; Chapter 25: Familial Cancer Syndromes With Cutaneous Manifestations (supporting context).