A 3-month-old girl was referred for recurrent fever, pneumonia, diarrhea, chronic dermatitis, failure to thrive, and motor retardation. The patient was the daughter of consanguineous parents and had a female sibling who had died due to recurrent infections. She suffered from oral thrush and a diffuse brownish colored macular rash on the trunk. Chest auscultation revealed bilateral crackles at the lower zones. Chest X-ray, indicated the absence of thymus shadow; a para-cardiac infiltration and an inferolateral squaring scapulae were demonstrated.Laboratory tests revealed mild anemia with profound lymphocytopenia, and hypogammaglobulinemia. adenosine deaminase (ADA) enzyme activities were low.What is the diagnosis?