**4.1 Incidence and clinical phenotypes**

The incidence of the classic WAS phenotype has been estimated at 1 in 100,000 individuals. Based on clinical manifestations, WAS-XLT commonly is presented at birth and consists of bruising, bloody diarrhea as well as petechiae. Excessive bleeding consequent circumcision can be considered as an early diagnostic sign. Furthermore, during infancy and childhood, eczema is a frequent manifestation of patients with classic WAS. Small platelet and thrombocytopenia are the most reliable finding in WAS and XLT phenotype. A variety of infections such as bacterial pneumonia, skin infections as well as otitis media with drainage of mucoid material are common complaints. XLT patients are less likely to have problems such as eczema and infection and oftentimes are misdiagnosed with Idiopathic thrombocytopenic purpura (ITP). Patients with X-linked neutropenia caused by missense mutations in the Cdc42-binding domain are affected at birth. However, their symptoms do not resemble those of classic WAS or XLT. Through a simple scoring system, we have delineated different clinical phenotypes (**Table 1**).
