Adenosine deaminase 2 (ADA2) deficiency is a disorder characterized by abnormal inflammation of various tissues. Signs and symptoms can begin anytime from early childhood to adulthood. The severity of the disorder also varies, even among affected individuals in the same family.

Inflammation is a normal immune system response to injury and foreign invaders (such as bacteria). However, ADA2 deficiency causes abnormal, unprovoked inflammation that can damage the body's tissues and organs, particularly blood vessels. (Inflammation of blood vessels is known as vasculitis.) Other tissues affected by abnormal inflammation can include the skin, gastrointestinal system, liver, kidneys, and nervous system. Depending on the severity and location of the inflammation, the disorder can cause disability or be life-threatening.

Signs and symptoms that can occur with ADA2 deficiency include fevers that are intermittent, meaning they come and go; areas of net-like, mottled skin discoloration called livedo racemosa; an enlarged liver and spleen (hepatosplenomegaly); and recurrent strokes affecting structures deep in the brain that can start in the first few years of life. In some people, ADA2 deficiency causes additional immune system abnormalities that increase the risk of bacterial and viral infections.

ADA2 deficiency is sometimes described as a form of polyarteritis nodosa (PAN), a disorder that causes inflammation of blood vessels throughout the body (systemic vasculitis). However, not all researchers classify ADA2 deficiency as a type of PAN.

More than 160 individuals with ADA2 deficiency have been described in the medical literature. However, researchers suspect that many more people may be affected, and ADA2 deficiency may not be a rare disease. They are working to determine whether this condition could underlie other, more common forms of vasculitis and stroke whose causes are currently unknown.

ADA2 deficiency is caused by mutations in the ADA2 gene. This gene provides instructions for making an enzyme called adenosine deaminase 2. Studies suggest that this enzyme plays an essential role in the growth and development of certain immune system cells, including macrophages, which are a type of white blood cell that plays a critical role in inflammation. Some macrophages are pro-inflammatory, meaning they promote inflammation, while others are anti-inflammatory, meaning they reduce inflammation.

Mutations in the ADA2 gene severely reduce or eliminate the activity of adenosine deaminase 2. Researchers do not fully understand how a shortage (deficiency) of this enzyme's activity leads to vasculitis and immune system abnormalities. They speculate that the enzyme deficiency may disrupt the balance between pro-inflammatory and anti-inflammatory macrophages in various tissues, leading to a buildup of pro-inflammatory macrophages and abnormal inflammation.

Genetic Testing Information

• Genetic Testing Registry: Sneddon syndrome
• Genetic Testing Registry: Vasculitis due to ADA2 deficiency

Genetic and Rare Diseases Information Center

• Polyarteritis nodosa
• Sneddon syndrome
• Vasculitis due to ADA2 deficiency

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Catalog of Genes and Diseases from OMIM

• SNEDDON SYNDROME; SNDNS
• VASCULITIS, AUTOINFLAMMATION, IMMUNODEFICIENCY, AND HEMATOLOGIC DEFECTS SYNDROME; VAIHS

Scientific Articles on PubMed

• PubMed

• Caorsi R, Penco F, Grossi A, Insalaco A, Omenetti A, Alessio M, Conti G, Marchetti F, Picco P, Tommasini A, Martino S, Malattia C, Gallizzi R, Podda RA, Salis A, Falcini F, Schena F, Garbarino F, Morreale A, Pardeo M, Ventrici C, Passarelli C, Zhou Q, Severino M, Gandolfo C, Damonte G, Martini A, Ravelli A, Aksentijevich I, Ceccherini I, Gattorno M. ADA2 deficiency (DADA2) as an unrecognised cause of early onset polyarteritis nodosa and stroke: a multicentre national study. Ann Rheum Dis. 2017 Oct;76(10):1648-1656. doi: 10.1136/annrheumdis-2016-210802. Epub 2017 May 18. Citation on PubMed
• Garg N, Kasapcopur O, Foster J 2nd, Barut K, Tekin A, Kizilkilic O, Tekin M. Novel adenosine deaminase 2 mutations in a child with a fatal vasculopathy. Eur J Pediatr. 2014 Jun;173(6):827-30. doi: 10.1007/s00431-014-2320-8. Epub 2014 Apr 16. Citation on PubMed
• Meyts I, Aksentijevich I. Deficiency of Adenosine Deaminase 2 (DADA2): Updates on the Phenotype, Genetics, Pathogenesis, and Treatment. J Clin Immunol. 2018 Jul;38(5):569-578. doi: 10.1007/s10875-018-0525-8. Epub 2018 Jun 27. Citation on PubMed
• Nanthapisal S, Murphy C, Omoyinmi E, Hong Y, Standing A, Berg S, Ekelund M, Jolles S, Harper L, Youngstein T, Gilmour K, Klein NJ, Eleftheriou D, Brogan PA. Deficiency of Adenosine Deaminase Type 2: A Description of Phenotype and Genotype in Fifteen Cases. Arthritis Rheumatol. 2016 Sep;68(9):2314-22. doi: 10.1002/art.39699. Citation on PubMed
• Navon Elkan P, Pierce SB, Segel R, Walsh T, Barash J, Padeh S, Zlotogorski A, Berkun Y, Press JJ, Mukamel M, Voth I, Hashkes PJ, Harel L, Hoffer V, Ling E, Yalcinkaya F, Kasapcopur O, Lee MK, Klevit RE, Renbaum P, Weinberg-Shukron A, Sener EF, Schormair B, Zeligson S, Marek-Yagel D, Strom TM, Shohat M, Singer A, Rubinow A, Pras E, Winkelmann J, Tekin M, Anikster Y, King MC, Levy-Lahad E. Mutant adenosine deaminase 2 in a polyarteritis nodosa vasculopathy. N Engl J Med. 2014 Mar 6;370(10):921-31. doi: 10.1056/NEJMoa1307362. Epub 2014 Feb 19. Citation on PubMed
• Van Montfrans JM, Hartman EA, Braun KP, Hennekam EA, Hak EA, Nederkoorn PJ, Westendorp WF, Bredius RG, Kollen WJ, Scholvinck EH, Legger GE, Meyts I, Liston A, Lichtenbelt KD, Giltay JC, Van Haaften G, De Vries Simons GM, Leavis H, Sanders CJ, Bierings MB, Nierkens S, Van Gijn ME. Phenotypic variability in patients with ADA2 deficiency due to identical homozygous R169Q mutations. Rheumatology (Oxford). 2016 May;55(5):902-10. doi: 10.1093/rheumatology/kev439. Epub 2016 Feb 10. Citation on PubMed
• Zhou Q, Yang D, Ombrello AK, Zavialov AV, Toro C, Zavialov AV, Stone DL, Chae JJ, Rosenzweig SD, Bishop K, Barron KS, Kuehn HS, Hoffmann P, Negro A, Tsai WL, Cowen EW, Pei W, Milner JD, Silvin C, Heller T, Chin DT, Patronas NJ, Barber JS, Lee CC, Wood GM, Ling A, Kelly SJ, Kleiner DE, Mullikin JC, Ganson NJ, Kong HH, Hambleton S, Candotti F, Quezado MM, Calvo KR, Alao H, Barham BK, Jones A, Meschia JF, Worrall BB, Kasner SE, Rich SS, Goldbach-Mansky R, Abinun M, Chalom E, Gotte AC, Punaro M, Pascual V, Verbsky JW, Torgerson TR, Singer NG, Gershon TR, Ozen S, Karadag O, Fleisher TA, Remmers EF, Burgess SM, Moir SL, Gadina M, Sood R, Hershfield MS, Boehm M, Kastner DL, Aksentijevich I. Early-onset stroke and vasculopathy associated with mutations in ADA2. N Engl J Med. 2014 Mar 6;370(10):911-20. doi: 10.1056/NEJMoa1307361. Epub 2014 Feb 19. Citation on PubMed or Free article on PubMed Central