Yoichi Wada1, Atsuo Kikuchi2, Natsuko Arai-Ichinoi1, Osamu Sakamoto1, Yusuke Takezawa1, Shinya Iwasawa1, Tetsuya Niihori3, Hiromi Nyuzuki4, Yoko Nakajima5, Erika Ogawa6, Mika Ishige6, Hiroki Hirai7, Hideo Sasai8, Ryoji Fujiki9, Matsuyuki Shirota10, Ryo Funayama11, Masayuki Yamamoto12, Tetsuya Ito5, Osamu Ohara9, Keiko Nakayama11, Yoko Aoki3, Seizo Koshiba12, Toshiyuki Fukao8, Shigeo Kure1,12. 1. Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan. 2. Department of Pediatrics, Tohoku University School of Medicine, Sendai, Japan. akikuchi-thk@umin.ac.jp. 3. Department of Medical Genetics, Tohoku University School of Medicine, Sendai, Japan. 4. Department of Pediatrics, Niigata University School of Medicine, Niigata, Japan. 5. Department of Pediatrics, Fujita Health University School of Medicine, Toyoake, Japan. 6. Department of Pediatrics and Child Health, Nihon University School of Medicine, Tokyo, Japan. 7. Department of Pediatrics, Ehime Prefectural Central Hospital, Matsuyama, Japan. 8. Department of Pediatrics, Graduate School of Medicine, Gifu University, Gifu, Japan. 9. Department of Technology Development, Kazusa DNA Research Institute, Kisarazu, Japan. 10. Division of Interdisciplinary Medical Sciences, United Centers for Advanced Research and Translational Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan. 11. Division of Cell Proliferation, United Centers for Advanced Research and Translational Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan. 12. Tohoku Medical Megabank Organization, Tohoku University, Sendai, Japan.
Abstract
PURPOSE: Galactosemia is caused by metabolic disturbances at various stages of galactose metabolism, including deficiencies in enzymes involved in the Leloir pathway (GALT, GALK1, and GALE). Nevertheless, the etiology of galactosemia has not been identified in a subset of patients. This study aimed to explore the causes of unexplained galactosemia. METHODS: Trio-based exome sequencing and/or Sanger sequencing was performed in eight patients with unexplained congenital galactosemia. In vitro enzymatic assays and immunoblot assays were performed to confirm the pathogenicity of the variants. RESULTS: The highest blood galactose levels observed in each patient were 17.3-41.9 mg/dl. Bilateral cataracts were observed in two patients. In all eight patients, we identified biallelic variants (p.Arg82*, p.Ile99Leufs*46, p.Gly142Arg, p.Arg267Gly, and p.Trp311*) in the GALM encoding galactose mutarotase, which catalyzes epimerization between β- and α-D-galactose in the first step of the Leloir pathway. GALM enzyme activities were undetectable in lymphoblastoid cell lines established from two patients. Immunoblot analysis showed the absence of the GALM protein in the patients' peripheral blood mononuclear cells. In vitro GALM expression and protein stability assays revealed altered stabilities of the variant GALM proteins. CONCLUSION: Biallelic GALM pathogenic variants cause galactosemia, suggesting the existence of type IV galactosemia.
PURPOSE: Galactosemia is caused by metabolic disturbances at various stages of galactose metabolism, including deficiencies in enzymes involved in the Leloir pathway (GALT, GALK1, and GALE). Nevertheless, the etiology of galactosemia has not been identified in a subset of patients. This study aimed to explore the causes of unexplained galactosemia. METHODS: Trio-based exome sequencing and/or Sanger sequencing was performed in eight patients with unexplained congenital galactosemia. In vitro enzymatic assays and immunoblot assays were performed to confirm the pathogenicity of the variants. RESULTS: The highest blood galactose levels observed in each patient were 17.3-41.9 mg/dl. Bilateral cataracts were observed in two patients. In all eight patients, we identified biallelic variants (p.Arg82*, p.Ile99Leufs*46, p.Gly142Arg, p.Arg267Gly, and p.Trp311*) in the GALM encoding galactose mutarotase, which catalyzes epimerization between β- and α-D-galactose in the first step of the Leloir pathway. GALM enzyme activities were undetectable in lymphoblastoid cell lines established from two patients. Immunoblot analysis showed the absence of the GALM protein in the patients' peripheral blood mononuclear cells. In vitro GALM expression and protein stability assays revealed altered stabilities of the variant GALM proteins. CONCLUSION: Biallelic GALM pathogenic variants cause galactosemia, suggesting the existence of type IV galactosemia.
Authors: Minela Haskovic; Ana I Coelho; Jörgen Bierau; Jo M Vanoevelen; Laura K M Steinbusch; Luc J I Zimmermann; Eduardo Villamor-Martinez; Gerard T Berry; M Estela Rubio-Gozalbo Journal: J Inherit Metab Dis Date: 2020-01-14 Impact factor: 4.982
Authors: Can Ficicioglu; Didem Demirbas; Britt Derks; G Shashidhar Pai; David J Timson; Maria Estela Rubio-Gozalbo; Gerard T Berry Journal: JIMD Rep Date: 2021-02-03