Recently, a recurrent heterozygous dominant 42 negative de novo mutation in TCF3 (Transcription Factor 3) gene (OMIM*147141) was 43 identified in four unrelated patients presenting with autosomal dominant 44 agammaglobulinemia.2 Herein, we report a patient with a novel homozygous nonsense 45 mutation in TCF3 gene, who presented with severe hypogammaglobulinemia and developed 46 B-cell acute lymphoblastic leukemia (ALL).