Different Phenotypes of Schimke Immuno-Osseous Dysplasia (SIOD) in Two Sisters with the Same Mutation in the SMARCAL1 Gene

Background: Schimke immuno-osseous dysplasia (SIOD) is a very rare autosomal recessive genetic disease caused by mutations in the SMARCAL1 gene. It is characterized by spondyloepiphyseal dysplasia, T-cell immunodeficiency, hypercromic nevi, hypercholestero-lemia, and steroid-resistant nephrotic syndrome with progressive renal failure to end-stage kidney disease. Case Presentation: We report two cases of SIOD in sisters, diagnosed after the debut of nephrotic syndrome. Both had a personal history of short stature, acetabular hip dysplasia, and hypercholesterolemia. The first case, a 6-year-old girl, presented peripheral refractory edema, severe arterial hypertension, and progressive decrease of the glomerular filtration rate. Steroid-resistance of nephrotic syndrome was confirmed, treated with tacrolimus without response. Renal function worsened over the following 4 months, so haemodialysis was started. Her sister, a 5-year-old girl, had the steroid-resistant nephrotic syndrome and normal blood pressure and renal function under enalapril treatment. In view of the suspicion of SIOD, genetic studies were carried out, revealing the same mutation in homozygosis. Conclusion: SIOD has a variable expression with multi-systemic involvement with a short life expectancy. Early diagnosis is important, which can encourage the early start of treatment and anticipation of complications that may be life-threatening.