Case report Histological, biochemical, and genetic characterization of early-onset fulminating sialidosis type 2 in a Korean neonate with hydrops fetalis Beom Hee Lee a , Yoo-Mi Kim a , Joo Hyun Kim c , Gu-Hwan Kim b , Byong Sop Lee a , Chong Jai Kim d , Hyun Ju Yoo e , Han-Wook Yoo a,⇑ a Department of Pediatrics, Asan Medical Center Children’s Hospital, University of Ulsan College of Medicine, Seoul, Republic of Korea b Medical Genetics Center, Asan Medical Center Children’s Hospital, University of Ulsan College of Medicine, Seoul, Republic of Korea c Genome Research Center for Birth Defects and Genetic Disorders, Asan Medical center, University of Ulsan College of Medicine, Seoul, Republic of Korea d Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea e Biomedical Research Center, Asan Institute of Life Sciences, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea Received 23 October 2012; received in revised form 23 December 2012; accepted 27 January 2013 Abstract Non-immune hydrops fetalis is the most severe presenting feature of lysosomal storage disorders. However, it is difficult to iden- tify the underlying condition because the different lysosomal storage diseases share many clinical features. A neonate with hydrops fetalis is described here. A lysosomal storage disorder was first suspected when the placental biopsy showed the presence of mac- rophages containing numerous cytoplasmic vacuoles. Subsequent comprehensive diagnostic processes and biochemical and molec- ular genetics characterization revealed a rare genetic cause, namely sialidosis type 2. Liquid chromatography–mass spectrometry revealed increased amounts of bound sialic acid in the urine. Pathogenic NEU1 mutations were detected. This is the first case with sialidosis type 2 ever known in the Korean population, exhibiting its most severe manifestation. Ó 2013 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved. Keywords: Hydrops fetalis; Sialidosis; Placental biopsy 1. Introduction Non-immune hydrops fetalis is the most severe feature of lysosomal storage disorders (LSD). These include Gaucher disease, Niemann–Pick disease type A, Wolman disease, mucolipidosis II, galactosialidosis, GM 1 ganglio- sidosis, sialidosis, and sialuria [1]. Although LSDs account only for a small proportion (15%) of hydrops fetalis causes, the development of biochemical and molec- ular testing strategies has increased the identification of these cases [2,3]. However, it is difficult to identify the underlying condition because the LSDs share many non-specific clinical features. Moreover, it is not easy to rule out all LSDs, especially when an appropriate test panel is unavailable. In this report, a neonate with hydrops fetalis is described. Comprehensive diagnostic processes after placental biopsy revealed a rare genetic cause, namely sialidosis type 2. This is the first case with sialidosis type 2 ever known in the Korean population, exhibiting its most severe manifestation. 0387-7604/$ - see front matter Ó 2013 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.braindev.2013.01.012 ⇑ Corresponding author. Address: Department of Paediatrics, Asan Medical Centre, University of Ulsan College of Medicine, 88, Olympic-Ro 43-Gil, Songpa-Gu, Seoul 138-736, Republic of Korea. Tel.: +82 2 3010 3374. E-mail address: hwyoo@amc.seoul.kr (H.-W. Yoo). www.elsevier.com/locate/braindev Brain & Development 36 (2014) 171–175