Adenosine deaminase deficiency

00:00 / 00:00



Adenosine deaminase deficiency

Immune system


Adenosine deaminase deficiency


0 / 10 complete

USMLE® Step 1 questions

0 / 3 complete

High Yield Notes

3 pages


Adenosine deaminase deficiency

of complete


USMLE® Step 1 style questions USMLE

of complete

A 6-month-old girl is brought to the physician due to persistent diarrhea for months. She has been hospitalized three times in the last two months due to respiratory infections that required intravenous antibiotics. Temperature is 37.8°C (100°F), blood pressure is 98/56 mmHg, and pulse is 110/min. On physical examination, the tonsils are absent. An eczematous rash is noticed over the face, limbs, and trunk. She is at the 4th percentile for weight and 5th percentile for height. Both parents are healthy; however, the patient had a brother who died at the age of two due to a severe respiratory infection. Laboratory testing is shown below. Which of the following best explains this patient's condition?

Laboratory Value  Result 
 Hemoglobin   10 g/dL 
 Mean corpuscular volume  90 fL 
 Neutrophil count  1000/mm3  
 T lymphocyte count   300/mm3 
 B lymphocyte count   170/mm3 
 Platelet count   160,000/mm3 

External References

First Aid








Adenosine deaminase deficiency p. 35, 115

Autosomal recessive disorders

adenosine deaminase deficiency p. 115

SCID (severe combined immunodeficiency disease) p. 96, 115

adenosine deaminase deficiency as cause p. 35


Adenosine deaminase deficiency, or ADA deficiency, is a rare genetic disease, that results in severe combined immunodeficiency, or SCID for short.

SCID can be caused by a number of causes, so this particular variation is called ADA-SCID.

Let’s take a step back. Our cells have all the instructions on how to live and behave written on their own copy of DNA.

DNA is made out of four nucleotides, which can also do all kinds of cool stuff in their free time, like provide energy to various processes in the cell.

Nucleotides are made out of a sugar, in this case deoxyribose, one to three phosphate groups, and a nucleobase, which can be adenine, thymine, cytosine, or guanine.

So, the name of a deoxyribose-containing, triphosphatic nucleotide, based on adenine, that makes up DNA would be deoxyadenosine triphosphate, or dATP, for short.

These nucleotides are needed in equal proportions in order to make cellular division run smoothly.

Now, nucleotides have a functional lifetime of their own, and our body has mechanisms on how to break them up into their building blocks, to be either excreted or recycled.

Let’s focus on deoxyadenosine triphosphate.

First the enzyme adenosine deaminase removes an amine group from it, turning it into deoxyinosine monophosphate, or dIMP.

Then purine nucleoside phosphorylase comes in and removes the phosphate and the deoxyribose from dIMP, making hypoxanthine.

Hypoxanthine is then oxidised twice by xanthine oxidase - first to become xanthine, and then finally, to uric acid.

Uric acid can then be excreted by the kidneys, in the form of urine.

Now one class of cells that divides quickly and therefore relies heavily on cell division to work smoothly are lymphocytes.

Lymphocytes protect the body from pathogens, like bacteria and viruses in two ways.

First, B lymphocytes, or B cells, produce immune proteins called antibodies, which seek out and latch on onto an invader, marking it for destruction by other cells.

Second, cytotoxic T lymphocytes, or cytotoxic T cells, as well as lymphocytes called natural killer cells, go cell to cell, looking for virally-infected cells or cells that look like they’ve started dividing uncontrollably - like a cancer cell.


  1. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  2. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  3. "Yen & Jaffe's Reproductive Endocrinology" Saunders W.B. (2018)
  4. "Bates' Guide to Physical Examination and History Taking" LWW (2016)
  5. "Robbins Basic Pathology" Elsevier (2017)
  6. "Adenosine deaminase deficiency: Frequency and comparative pathology in autosomally recessive severe combined immunodeficiency" Clinical Immunology and Immunopathology (1979)
  7. "Educational paper" European Journal of Pediatrics (2011)
  8. "Development of gene therapy: potential in severe combined immunodeficiency due to adenosine deaminase deficiency" Stem Cells and Cloning: Advances and Applications (2009)
  9. "Management options for adenosine deaminase deficiency; proceedings of the EBMT satellite workshop (Hamburg, March 2006)" Clinical Immunology (2007)

Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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.