A 7 month old boy is brought to pediatrics emergency by his parents with chief complaints of runny nose, cough and failure to thrive. On examination, the following lesion is noted with absence of tonsils and lymph nodes. Chest x ray is performed with following findings. Laboratory tests revealed marked lymphopenia. The child improved on TMP-SMX therapy. Which of the following will not be a differential diagnosis in above clinical scenario?

The failure to thrive, thrush and CXR with symmetrical interstitial radio-opacities-likely pneumonia. As patient is improving with TMP-SMX , it is s/o pneumocystis jerovecii as diagnosis. The differential diagnosis are: HIV infection SCID Bare lymphocyte syndrome Ataxia telengectasia Atypical digeorge syndrome(thymic aplasia) SCIDs characterized by: Block in T cell development and thus the complete absence of these cells. Clinical manifestations are: recurrent oral candidiasis failure to thrive protracted diarrhea acute interstitial pneumonitis caused by Pneumocystis jiroveci Lymphocytopenia is s/o SCID in >90% of cases. Thymic shadow is absent on a chest x-ray may be suggestive of SCID. T cell quantification of receptor excision circles (TREC) by using the Guthrie card is a reliable diagnostic test for newborn screening.