Which of the following is a classic symptom of Wiskott-Aldrich syndrome?

Wiskott-Aldrich syndrome is characterized by a triad of symptoms: eczema, recurrent infections, and thrombocytopenia. Thrombocytopenia, which refers to a low platelet count, is a hallmark feature of this X-linked immunodeficiency disorder. The low platelet count leads not only to an increased risk of bleeding but also reflects the underlying bone marrow failure that affects normal platelet production. The other symptoms associated with Wiskott-Aldrich syndrome can include eczema and increased susceptibility to infections, but the key distinguishing feature that validates the diagnosis of this condition is indeed thrombocytopenia. Other options such as bronchial asthma, persistent diarrhea, and congenital heart defects, while they may be seen in various immunodeficiency or other syndromic conditions, are not classic or defining symptoms of Wiskott-Aldrich syndrome. Thus, thrombocytopenia stands out as the most recognizable and critical symptom associated with this genetic disorder.