A Novel Mutation in the INSR Causes Severe Insulin Resistance and Rabson-Mendenhall Syndrome in a Paraguayan Patient

Rabson-Mendenhall syndrome is a rare autosomal recessive disorder characterized by severe insulin resistance, resulting in early-onset diabetes mellitus. We are reporting the first case of Rabson-Mendenhall syndrome in a Paraguayan patient. The patient is a 5-year-old girl who presented with hypertrichosis, acanthosis nigricans, and nephrocalcinosis. Genetic testing by NGS revealed two pathogenic variants in exons 2 and 18 of the INSR gene; c.332G>T (p. Gly111Val) and c.3485C>T (p. Ala1162Val), in combined heterozygosis. The novel INSR c. 332G>T variant leads to the substitution of glycine to valine at position 111 in the protein, and multiple in silico software predicted it as pathogenic. The c. 3485C>T variant leads to the substitution of alanine to valine at position 1162 in the protein previously described for insulin resistance and Rabson-Mendenhall syndrome. The management of Rabson-Mendenhall syndrome is particularly challenging in children, and the use of metformin is often limited by its side effects. The patient was managed with nutritional measures due to the early age of onset. This report expands the knowledge of Rabson-Mendenhall syndrome to the Paraguayan population and adds a novel pathogenic variant to the existing literature.