en Genetics & Disease Genetics & Disease Case Report Case Report <div style="text-align: justify;">Mucopolysaccharidosis type IIIC (MPSIIIC) is a rare subtype of mucopolysaccharidosis disorder family caused by mutations in heparan-alpha-glucosaminide N-acetyltransferase (HGSNAT) gene. MPSIIIC is subdivided into four subtypes which have overlapping features, and are indistinguishable at clinical level. In populations with high consanguineous marriage rate, homozygosity mapping can be a good choice for finding a disease locus. Herein we report a female patient with a novel mutation in HGSNAT gene in Iranian population. Clinical diagnosis was accomplished based on clinical manifestations, and urine biochemical analysis. Homozygosity mapping was performed using SNP- array technology to narrow down the candidate locus. All coding exons of HGSNAT were scanned by direct DNA sequencing. We found a novel ins/del mutation as c.1357TA>C. This mutation is a frameshift which eventually leads to premature protein truncation. To the best of our knowledge this is the first case report of Sanfilippo type C in Iranian population. This result also supports the applicability of homozygosity mapping to the diagnosis of Sanfilippo subtype.</div> Mucopolysaccharidosis type IIIC, HGSNAT, homozygosity mapping, SNP-array, mutation detection 117 121 http://ibbj.org/browse.php?a_code=A-10-288-1&slc_lang=en&sid=1 Atieh Eslahi atiye.eslahi69@gmail.com 10031947532846003252 10031947532846003252 No Department of Medical Genetics, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Farah Ashrafzadeh ashrafzadehf@mums.ac.ir 10031947532846003253 10031947532846003253 No Department of Pediatric Neurology, Ghaem Medical Center, Mashhad University of Medical Sciences, Mashhad, Iran. Kazem Hasanpour hasanpourk@mums.ac.ir 10031947532846003254 10031947532846003254 No Department of Clinical Sciences, Sabzevar University of Medical Sciences, Sabzevar, Iran. Majid Mojarrad majidmojarrad@gmail.com 10031947532846003255 10031947532846003255 Yes Medical Genetics Research Center, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Nedasadat Hosseini ns.vh.hosseini@gmail.com 10031947532846003256 10031947532846003256 No Department of Medical Genetics, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.