00:00 / 00:00





General infections


Neonatal sepsis


Hypersensitivity reactions

Type I hypersensitivity

Food allergy



Type II hypersensitivity

Immune thrombocytopenic purpura

Autoimmune hemolytic anemia

Hemolytic disease of the newborn

Goodpasture syndrome

Rheumatic heart disease

Myasthenia gravis

Graves disease

Pemphigus vulgaris

Type III hypersensitivity

Serum sickness

Systemic lupus erythematosus

Poststreptococcal glomerulonephritis

Type IV hypersensitivity

Graft-versus-host disease

Contact dermatitis


Transplant rejection

Graft-versus-host disease

Cytomegalovirus infection after transplant (NORD)

Post-transplant lymphoproliferative disorders (NORD)


X-linked agammaglobulinemia

Selective immunoglobulin A deficiency

Common variable immunodeficiency

IgG subclass deficiency

Hyperimmunoglobulin E syndrome

Isolated primary immunoglobulin M deficiency

Thymic aplasia

DiGeorge syndrome

Severe combined immunodeficiency

Adenosine deaminase deficiency


Hyper IgM syndrome

Wiskott-Aldrich syndrome

Leukocyte adhesion deficiency

Chediak-Higashi syndrome

Chronic granulomatous disease

Complement deficiency

Hereditary angioedema


Immune system organ disorders


Ruptured spleen

Immune system pathology review

Blood transfusion reactions and transplant rejection: Pathology review

Immunodeficiencies: T-cell and B-cell disorders: Pathology review

Immunodeficiencies: Combined T-cell and B-cell disorders: Pathology review

Immunodeficiencies: Phagocyte and complement dysfunction: Pathology review




0 / 8 complete

USMLE® Step 1 questions

0 / 1 complete

High Yield Notes

13 pages



of complete


USMLE® Step 1 style questions USMLE

of complete

An 8-year-old girl is brought to her primary care physician's office for evaluation of unsteady gait. The parent states the patient’s gait has become “wobbly,” and she has been experiencing recurrent falls. The parent also reports it is difficult to understand her speech. Her development was normal until the age of two years, when she started developing these symptoms. Past medical history is significant for recurrent respiratory tract infections. Family history is unremarkable. Vitals are within normal limits. Physical examination demonstrates numerous superficial nests of distended blanchable capillaries on sun-exposed areas. The patient is unable to coordinate head and eye movements when shifting gaze. This patient is at increased risk of developing which of the following complications?

External References

First Aid









ataxia-telangiectasia p. 115


ataxia-telangiectasia p. 38

Ataxia-telangiectasia p. 37, 115

IgA antibodies p. 103

ataxia-telangiectasia p. 115

IgE antibodies p. 103

ataxia-telangiectasia p. 115

IgG antibodies p. 103

ataxia-telangiectasia p. 115

Lymphopenias p. 431

ataxia-telangiectasia p. 115

Spider angiomas

ataxia-telangiectasia p. 115



Thomas Bush

Sam Gillespie, BSc

Tanner Marshall, MS

With ataxia telangiectasia, ataxia refers to poor coordination and telangiectasia refers to dilated blood vessels, which are the two key symptoms of this disease.

Ataxia telangiectasia develops when a genetic mutation causes the lack of a protein called ataxia telangiectasia mutated serine-threonine kinase, or just ATM for short, which normally fixes up damaged DNA.

DNA of every cell gets damaged over and over again from various environmental factors like radiation and chemical toxins.

Now, one of the most severe types DNA damage is a double-strand break, where both strands of the DNA’s double helix are severed, damaging the genetic information that was stored there. To help with this sort of repair, there’s a protein called ATM.

ATM is primarily located in the cell's nucleus, and you can sort of think of ATM as like a manager of the DNA’s repair.

It’s protein kinase, which means that it uses it’s managing skills to activate other proteins through phosphorylation, which is the addition of a phosphoryl or -PO32− group.

So at the site of the double strand break, ATM phosphorylates proteins like the tumor suppressor protein p53, that stop the cell from reproducing.

ATM also phosphorylates additional proteins which will either fix the DNA or kill the faulty cell through a process of apoptosis - controlled cell death. This way we don't end up with a bunch of defective cells trying to reproduce.

That's the main role of ATM, but it also plays a role in the development of immune cells, especially T lymphocytes.

T lymphocytes need to be able to recognize a wide variety of antigens, and to do this, they purposefully create double strand breaks in their DNA during development. That way parts of their DNA can get rearranged, and code for new and unique antigen receptors.

Once again, ATM helps to fix these breaks - and that keeps the T-cells functioning normally.

In ataxia telangiectasia, there's an autosomal recessive mutation of the ATM gene.

This leads to a decrease in the amount of functioning ATM protein, and as a result, cells that undergo a double-strand break don't have sufficient ATM to repair the break.

As a result, some of the damaged cells might survive and continue to proliferate despite the damage, but most ultimately die off.


Ataxia-telangiectasia (A-T) also called Louis-Bar Syndrome, is an autosomal recessive condition characterized by progressive cerebellar atrophy and oculocutaneous telangiectasia (small dilated vessels under the skin). People with A-T often have high rates of cancer and immunodeficiency disorders. It is caused by a mutation of the ataxia telangiectasia mutated (ATM) gene, and it is characterized by poor muscle coordination or ataxia (often needing a wheelchair by the age of 10), dysarthria, and telangiectasia on the skin and eyes.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "A Single Ataxia Telangiectasia Gene with a Product Similar to PI-3 Kinase" Science (1995)
  6. "Consequences of the Delayed Diagnosis of Ataxia-Telangiectasia" Pediatrics (1998)
  7. "Ataxia telangiectasia" Seminars in Pediatric Neurology (1998)
  8. "DNA damage-induced activation of ATM and ATM-dependent signaling pathways" DNA Repair (2004)
  9. "Early diagnosis of ataxia-telangiectasia using radiosensitivity testing" The Journal of Pediatrics (2002)

Copyright © 2023 Elsevier, except certain content provided by third parties

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.