Deficiency of Adenosine Deaminase 2 (DADA2) – aka Fever with Early Onset Stroke (FEOS)
Unknown but rare.
Livedo reticularis rash is common. A few with polyarteritis nodosa (PAN). Diffuse vasculopathy, with impaired endothelial integrity and endothelial cellular activation.   Predominant levels of neutrophils and macrophages in the interstitium; perivascular T lymphocytes, without obvious vasculitis. 
Recurrent fevers, and early-onset lacunar strokes is common. Some patients do not have strokes.  Possible adult stroke risk. Brain biopsies: diffuse vasculopathy, with impaired endothelial integrity and endothelial cellular activation.   The first stroke often occurs before 5 years of age. 
High: CRP, ESR with flares. Cytopenia. Blood: 10-fold decrease in ADA2. Low: IgM , ADA2-specific adenosine deaminase activity: blood & CD14+ monocytes.   Absence of hypercoagulability.  Negative for antiphospholipid antibodies (APLAs). Some patients later develop a positive lupus anticoagulant (LA) level. Some have mild immunodeficiency.
Deficiency of Adenosine Deaminase 2,DADA2,Fever Early Onset Stroke, FEOS, CECR1, ADA2 deficiency, ADA2, stroke, fever, periodic fever, recurrent fever, livedo reticularis, rash, vasculopathy, lacunar stroke, stroke child, stroke infant, livedo, lacy rash, web rash, polyarteritis nodosa,PAN, cytopenia, ADA2-specific adenosine deaminase, lupus anticoagulant, necrotizing vasculitis, portal hypertension, portal, hypertension, hepatosplenomegaly, hepatomegaly, splenomegaly, enlarged liver and spleen, enlarged liver, enlarged spleen, large liver and spleen, large liver, large spleen, immunodeficiency
Diepgen TL, Yihune G et al. Livedo Reticularis.. Dermatology Online Atlas. DermIS Dermatology Information System. Published online at: http://www.dermis.net/dermisroot/en/42791/image.htm.