LAUSR

To the Editor, ADA2 (previously known as CECR1, cat eye syndrome chromosome region, candidate 1) mutations encoding adenosine deaminase 2 (ADA2) were found to cause the first molecularly defined monogenic vasculitis syndrome [1, 2]. Initial patient reports described the condition as partially mimicking polyarteritis nodosa (PAN) with vasculitis and rashes in addition to systemic inflammation [3, 4]. However, subsequent publications unveiled a remarkable pleiotropy of this condition with affections of multiple organ systems, including the skin, the nervous system, the kidneys, and the gastrointestinal tract [4]. Hematological involvement can manifest as severe cytopenia and can also include immunological features like hypogammaglobulinemia and deficiencies in NK cells, T cells, and B cells, which may partially mimic a common variable immunodeficiency syndrome [4, 5]. The autosomal recessive disease is driven by a loss of function of the enzymatic capacity of the mainly extracellular enzyme ADA2 (reviewed in [3]). The large phenotypic variability of the disease poses a challenge for early clinical diagnosis, especially when diagnostic approaches are performed in a stepwise manner.