Identification of mutation in NPC2 by exome sequencing results in diagnosis of Niemann–Pick disease type C Afagh Alavi a , Shahriar Nafissi b , Hosein Shamshiri b , Maryam Malakooti Nejad c , Elahe Elahi a,c,d, ⁎ a School of Biology, College of Science, University of Tehran, Tehran, Iran b Department of Neurology, Tehran University of Medical Sciences, Tehran, Iran c Department of Biotechnology, College of Science, University of Tehran, Tehran, Iran d Center of Excellence in Phylogeny of Living Organisms in Iran, School of Biology, College of Science, University of Tehran, Tehran, Iran abstract article info Article history: Received 2 May 2013 Received in revised form 29 May 2013 Accepted 29 May 2013 Available online 6 June 2013 Keywords: Exome sequencing Niemann–Pick C NPC2 p.Pro120Ser We report identification of a homozygous mutation in NPC2 in two Iranian siblings with a neurologic dys- function whose disease had not been diagnosed prior to our genetic analysis. The mutation was identified by exome sequencing. The finding resulted in diagnosis of Niemann–Pick disease type C (NPC) in the siblings, and initiation of treatment with Miglustat. The clinical features of the patients are presented. It has been suggested that NPC is under diagnosed, particularly when presentations are not very severe, as was the sit- uation in the cases studied here. NPC is a fatal autosomal recessive disorder clinically characterized by hepatosplenomegaly and progressive neurological deterioration. At the cellular level, it causes aberrant cho- lesterol trafficking and accumulation of unesterified cholesterol in lysosomes. Mutations in NPC1 and NPC2 are cause of disease in respectively, 95% and 5% of NPC patients. The p.Pro120Ser causing mutation in NPC2 observed in the Iranian patients was earlier observed in the only other NPC2 patient reported from the Middle East. The study demonstrates that in addition to greatly facilitating gene discovery, exome sequencing has notable potentials for diagnosis, particularly for diagnosis of atypical cases. © 2013 Elsevier Inc. All rights reserved. 1. Introduction The name “Niemann–Pick disease” derives from the names of pediatrician Albert Niemann and pathologist Ludwig Pick who first described some of its clinical presentations [1]. The disease is now known to encompass several lysosomal lipid storage diseases. Vari- ability in presentation was recognized as early as 1961, when it was grouped into four subtypes A–D on the basis of rate of disease pro- gression and patterns of organ involvement and lipid storage in only 18 patients [2]. Subtypes A and B proved to be biochemically and genetically related, both being sphingomyelin storage disorders caused by mutations in SMPD1 that encodes sphingomyelin phospho- diesterase 1 [3,4]. Subtype C was later further subtyped NPC1 and NPC2 based on cell fusion complementation and genetic findings, and subtype D was shown to be allelic to NPC1 [5–7]. Niemann–Pick disease type C (NPC) is a fatal disorder clinically characterized by hepatosplenomegaly and progressive neurological deterioration. Age at onset of symptoms ranges from the perinatal period to adult age, and is most often before the age of 20 years [8]. Severity of disease, rate of progression, and duration till death are ad- ditional variant clinical features [8,9]. Its inheritance pattern is auto- somal recessive, and its prevalence among living births is estimated at 1/120,000 to 1/150,000 [10]. At the cellular level, NPC is character- ized by accumulation of unesterified cholesterol and glycolipids in ly- sosomes and late endosomes [11]. The precise pattern of stored lipids varies in different tissues [11–14]. Aberrant intracellular translocation of exogenous cholesterol is best evidenced in fibroblasts of NPC pa- tients by a specific pattern of fluorescence in a protocol that includes probing with filipin, a cholesterol binding antibiotic [15]. Exogenous cholesterol in the form of low density lipoprotein (LDL) appears to be normally internalized, transported to endocytic vesicles, and hy- drolyzed. However, transport of unesterified cholesterol out of lyso- somes to other cellular sites is impaired. Endogenously synthesized cholesterol may contribute to cholesterol accumulation in some cell types [16,17]. Furthermore, intracellular cholesterol homeostasis in- cluding cholesterol ester formation is delayed in NPC cells [18]. Two NPC causing genes have been identified. NPC1 (OMIM # 607623) which encodes an integral 1278 amino acid membrane pro- tein was discovered by linkage analysis [5,19]. The protein is found pri- marily in late endosomes and interacts transiently with lysosomes and Molecular Genetics and Metabolism 110 (2013) 139–144 Abbreviations: NPC, Niemann–Pick type C; NPC1, NPC1 gene; NPC2, NPC2 gene; SMPD1, sphingomyelin phosphodiesterase 1 gene; LDL, low density lipoprotein; HGMD, The Human Gene Mutation Database; ALS, amyotrophic lateral sclerosis; DTR, deep tendon reflex; MRI, magnetic resonance imaging; SOD1, Superoxide desmutase 1 gene; C9orf72, chromosome 9 open reading frame 72 gene; PCR-RFLP, polymerase chain reaction-restriction fragment length polymorphism. ⁎ Corresponding author at: University College of Science, University of Tehran, College of Science, University of Tehran, Enghelab Ave., Tehran 1417 614411, Iran. Fax: +98 2166405141. E-mail addresses: elaheelahi@ut.ac.ir, elahe.elahi@gmail.com (E. Elahi). 1096-7192/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ymgme.2013.05.019 Contents lists available at ScienceDirect Molecular Genetics and Metabolism journal homepage: www.elsevier.com/locate/ymgme