Riva E 1 , Gasparri M 1 , Giulini Neri I 1 , Paci S 1 1 Ped Dep, San Paolo Hosp, Univ of Milan, Milan, Italy Glycogen storage disease Ib (GSD Ib) is characterized, in addition to the signs and symptoms of GSD I, by recurrent infections and inflammatory bowel disease (IBD), associated with neutropenia/neutrophil dysfunction. MGUS (Monoclonal Gammopathy of Unknown Significance) is a biochemical condition without clinical expression often described in patient with chronic diseases, with higher risk of transformation in myeloma. There are no cases of MGUS in GSD Ib patients described in literature. We describe the case of a 31 years old boy with diagnosis of GSD Ib at 3 months of age and of IBD at the age of 19, when anti-inflammatory therapy was started. Since 2007 the protein electrophoresis showed a monoclonal not determinable IgAλ component. Since 2010 a policlonality, attributed to his chronic inflammatory condition, was evidenced. The plasma and urine determination of κ and λ light chains showed higher values than in the normal range, with a normal κ/λ rate and a monoclonal component lower than 1,5 g/dl. The patient doesn't show either kidney insufficient function or peripheral neuropathy or bone lesions. This report confirms that GSD Ib is a clinical condition that still needs further investigations in order to better understand its evolution in adult patients.