Wiskott-Aldrich syndrome (WAS) is a rare X-linked genetic disorder caused by a mutation in the WAS gene that codes for the WASp protein, which is involved in the functioning of the cytoskeleton of non-erythroid haematopoietic cells. This mutation leads to a congenital immunity disorder characterised by immunodeficiency, micro-thrombocytopenia and eczema. Its incidence is 1 in 250,000 live-born males. Treatment options to date are haematopoietic stem cell transplantation (HSCT) from an HLA-matched donor or gene therapy. The paper described the case of a 5-month-old first-born child with WAS who represented a diagnostic challenge. At onset, the infant did not present with any pathognomonic elements of classic WAS, but a picture of trilinear cytopenia with severe anaemia. Only one single case is described in literature with the same genotype (WAS c.257G>A p. Arg86His) but characterised by a heterogeneous phenotype and different onset symptoms. The specific and timely diagnosis of WAS allowed the patient, at only 5 months of age, to undergo gene therapy, thus achieving a real recovery from the syndrome and significantly reducing the risks related to the toxicity of non-targeted therapies to which he would have been ex-posed in the future.