Introduction: Wolfram syndrome (WS) is an autosomal recessive rare genetic disorder characterized by diabetes mellitus, diabetes insipidus, hearing loss, optic atrophy, and a variety of abnormalities of the urinary tract, nervous system, and endocrine glands. The WFS1 gene is mapped on chromosome 4p16 and consists of 8 exons and Exon 8 is the largest. WFS1 gene encodes an 890 residue glycoprotein wolframin, consists of three fragments, including cytoplasmic N-terminal domain, luminal C-terminus, and central nine-transmembrane domains, which is responsible for the regulation of endoplasmic reticulum (ER) stress, integrity, intracellular homeostasis, and survival of the cell. To date, over 200 WFS1 pathogenic and likely pathogenic mutations. The majority of them are located in exon 8, that encodes the C-terminal and transmembrane domain of the protein. WFS1 gene variants are heterogeneous and include a variety of non-sense, missense, and frameshift deletion or insertion mutations. Studying rare autosomal recessive disease in regions with consanguineous marriage, such as Iran can help us to prevention and management of this disease. In the present survey, we performed a genetic investigation on three families with WS and reported a novel mutation, and two previously reported mutation in the WFS1 gene.
Methods: In this study, we have performed Sanger sequencing and co-segregation analysis for three consanguineous Iranian families including three patients to identify the etiology of the disease in the patients. Bioinformatics tools were used to evaluate the pathogenicity of the identified variants.
Results: Sequencing results showed two known mutations ( c.2105G>A and c.2006A>G) and a novel homozygous stopgain mutation, c.1444A>T (p.K482X) in exon 8 of WFS1 gene. Bioinformatics studies verified the pathogenic effects of the novel variant. Finally, p.K482X is classified as a novel pathogen variant according to American College of Medical Genetics and Genomics (ACMG) guidelines. Further analysis demonstrated that both parents were heterozygous for the variant.
Conclusion: the novel mutation (p.K482X) creates a frameshift, which occurs in the transmembrane domain and causes the elimination of 46% of the WFS1 protein (Wolframin), leading to a premature stop codon truncating the protein in amino acid 482 residues. This mutation causes the loss of Wolframin protein function. Our data proved the importance of genetic analysis in patients with early onset of DM.