Novel IDS Variants Identified in Three Unrelated Pakistani Patients Affected with Mucopolysaccharidosis Type II (Hunter Syndrome)

Abstract

Introduction: Mucopolysaccharidosis type II (MPS-II) or Hunter syndrome is a rare X-linked recessive disorder caused by genetic lesions in the IDS gene, encoding the iduronate-2-sulfatase (IDS) enzyme, disrupting the metabolism of certain sulfate components of the extracellular matrix. Thus, the undegraded components, also known as glycosaminoglycans, accumulate in multiple tissues resulting in multisystemic abnormalities. Objective: To uncover causative genetic lesions in probands of three unrelated Pakistani families affected with rare X-linked recessive Hunter syndrome. Methods: Screening of the IDS gene was performed in six individuals (three patients and their mothers) through whole genomic DNA extraction from peripheral blood followed by PCR and Sanger sequencing. MutationTaster, PROVEAN, Human Splicing Finder, Swiss-Model, and SwissPdbViewer were used for in silico analysis of identified variants. Results: All probands were presented with coarse facies, recurrent respiratory tract infection, and reduced IDS activity. Molecular screening of IDS identified three different pathogenic variants including a novel duplication variant c.114_117dupCGTT, a novel splice site variant c.1006 + 1G>C, and a nonsense variant c.1165C>T. In silico analysis unanimously revealed the pathogenic nature of the variants due to their deleterious effects upon the encoded enzyme. Conclusion: Identified variants predictably lead to either the expression of a nonfunctional enzyme due to partial loss of SD1 and complete loss of SD2 subdomains or a complete lack of the IDS enzyme as a result of nonsense-mediated mRNA decay. Our study provides the first genetic depiction of MPS-II in Pakistan, expands the global IDS mutation spectrum, may provide insights into the three-dimensional structure of IDS, and should benefit the affected families in genetic counseling and prenatal diagnosis.