ORIGINAL RESEARCH Inflammatory Bowel Disease and T cell Lymphopenia in G6PC3 Deficiency Philippe Bégin & Natalie Patey & Pascal Mueller & Andrée Rasquin & Alain Sirard & Christoph Klein & Élie Haddad & Éric Drouin & Françoise Le Deist Received: 9 October 2012 / Accepted: 30 October 2012 / Published online: 20 November 2012 # Springer Science+Business Media New York 2012 Abstract Purpose G6PC3 deficiency presents as a complex and het- erogeneous syndrome that classically associates severe con- genital neutropenia with cardiac and urogenital developmental defects. Here we investigate the findings of T cell lymphope- nia and inflammatory bowel disease in a child with G6PC3 deficiency due to compound heterozygous mutations in intron 3 (c.IVS3-1 G>A) and exon 6 (c.G778G/C; p.Gly260/Arg). Methods Histological examination was conducted on all biopsy specimens. Immunophenotyping and lymphocyte proliferation assays were performed. Immunoglobulin levels and vaccine responses were measured. Results The patient showed persistent global T cell lympho- penia, with only 8 to 13 % of thymic naive CD31 + CD45RA + cells among CD4 T cells (normal range 27–60 %). Prolifera- tion assays and vaccine responses were within normal limits. The gastrointestinal inflammatory lesions were very closely related to those of glycogen storage disease type 1b, with a Crohn’ s-like appearance but without granuloma or increased cryptic abscesses. The gastrointestinal disease responded to infliximab therapy. These findings were associated with a polyclonal hypergammaglobuliemia G. Conclusion G6PC3 deficiency may present with inflamma- tory bowel disease and T cell lymphopenia. The diagnosis should thus be considered in a patient with chronic congen- ital neutropenia and gastrointestinal symptoms. Patients with confirmed disease should also undergo T cell pheno- typing to rule out cellular immunodeficiency. P. Bégin : P. Mueller : A. Sirard : É. Haddad : É. Drouin : F. Le Deist Department of Pediatrics, CHU Sainte-Justine and Université de Montréal, Montreal, Canada P. Bégin : É. Haddad Division of Immunology, Department of Pediatrics, CHU Sainte-Justine and Université de Montréal, Montreal, Canada P. Mueller : A. Rasquin : É. Drouin Division of Gastroenterology, Department of Pediatrics, CHU Sainte-Justine and Université de Montréal, Montreal, Canada A. Sirard Division of General Pediatrics, Department of Pediatrics, CHU Sainte-Justine and Université de Montréal, Montreal, Canada P. Bégin Centre de Recherche du Centre Hospitalier de l’Université de Montréal (CRCHUM), Montreal, Canada P. Bégin Division of Immunology, Centre Hospitalier de l’Université de Montréal (CHUM), Montreal, Canada N. Patey Department of Pathology, CHU Sainte-Justine and Université de Montréal, Montreal, Canada C. Klein University Children’ s Hospital, Ludwig Maximilians University, Munich, Germany É. Haddad : F. Le Deist (*) Department of Immunology and Microbiology, CHU Sainte-Justine and Université de Montréal, 3175, Côte Sainte-Catherine, Montreal, Québec, Canada H3T 1C5 e-mail: francoise.le.deist@umontreal.ca J Clin Immunol (2013) 33:520–525 DOI 10.1007/s10875-012-9833-6