Takashi Shoji ¹ Ichiro Yamauchi ^1* Hidenori Kawasaki ¹ Kogoro Iwanaga ¹ Takuro Hakata ¹ Daisuke Tanaka ¹ Junji Fujikura ¹ Toshihiko Masui ² Hisato Suzuki ³ Mamiko Yamada ³ Kenjiro Kosaki ³ Akira Inaba ⁴ Takahito Wada ¹ Shinji Kosugi ¹ Toshihito Fujii ¹ Daisuke Taura ¹ Nobuya Inagaki ¹

• ¹ Kyoto University, Kyoto, Kyōto, Japan
• ² Kurashiki Central Hospital, Kurashiki, Okayama, Japan
• ³ Keio University, Minato, Tōkyō, Japan
• ⁴ Kyoto University Hospital, Kyoto, Kyōto, Japan

Silver-Russell syndrome (SRS) is a syndrome characterized by prenatal and postnatal growth retardation, facial features, and body asymmetry. SRS is often complicated with hypoglycemia, whose etiology is unclear. We describe the clinical course of 25-year-old man with hypoglycemia. We diagnosed him with hyperinsulinemic hypoglycemia (HH) and treated him with laparoscopic distal pancreatectomy.Histological examination led to a diagnosis of nesidioblastosis. The juvenile onset of his nesidioblastosis and its slowly progressive course suggested a genetic etiology. Wholeexome sequencing (WES) identified the heterozygous NR0B2 Ala195Ser variant, which alone was unlikely to cause nesidioblastosis because this variant is sometimes detected in the Japanese population. Copy number analysis using WES data suggested duplication in chromosome 7, and subsequent G-banding chromosome analysis confirmed mos dup(7)(p11.2p14). We determined that the patient had SRS-like phenotype based on his clinical features and this duplication. Furthermore, we found that the duplicated region contained the GCK gene, whose gain-of function variants could cause HH. Taken together, the patient's HH may have been caused by duplication of the GCK gene, which could be a novel cause of nesidioblastosis.