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.

Context: Mutations in Cytochrome P450 oxidoreductase (POR) cause a form of congenital adrenal hyperplasia (CAH). We are reporting a novel R550W mutation in POR identified in a 46, XX patient with signs of aromatase deficiency. Objective: Analysis of aromatase deficiency from R550W mutation in POR. Design, Setting, and Patient: Both the child and the mother had signs of virilization. Ultrasound revealed the presence of uterus and ovaries. No defects in CYP19A1 were found, but further analysis with a targeted Disorders of Sexual Development NGS panel (DSDSeq.V1, 111 genes) on a NextSeq (Illumina) platform in Madrid and Barcelona, Spain, revealed compound heterozygous mutations c.73_74delCT/p.L25FfsTer93 and c.1648C>T/p.R550W in POR. WT and R550W POR were produced as recombinant proteins and tested with multiple cytochrome P450 enzymes at University Children’s Hospital, Bern, Switzerland. Main Outcome Measure and Results: R550W POR showed 41% of the WT activity in cytochrome c and 7.7% activity for reduction of MTT. Assays of CYP19A1 showed a severe loss of activity and CYP17A1, as well as CYP21A2 activities, were also lost by more than 95%. Loss of CYP2C9, CYP2C19, and CYP3A4 activities was observed for the R550W-POR. Predicted adverse effect on aromatase activity as well as a reduction in binding of NADPH was confirmed. Conclusions: Pathological effects due to POR R550W were identified, expanding the knowledge of molecular pathways associated with aromatase deficiency. Screening of the POR gene may provide a diagnosis in CAH without defects in genes for steroid metabolizing enzymes.

Steroidogenic factor 1 (SF-1) is a nuclear receptor that regulates steroidogenesis and reproductive development. NR5A1/SF-1 variants are associated with a broad spectrum of phenotypes across individuals with disorders of sex development (DSD). Oligogenic inheritance has been suggested as an explanation. However, testing the impact of specific gene variants involved in a network remains difficult. To confirm the hypothesis that NR5A1/SF-1-related DSD follow an oligogenic mode of inheritance, we investigated a constellation of gene variants identified in a 46,XY severely undervirilized individual. Candidate genes were revealed by whole exome sequencing, and pathogenicity was predicted by different in silico tools. We found variants in NR1H2 and INHA associated with steroidogenesis, sex development, and reproduction. Functional testing was conducted in cell models. Novel SF-1 and NR1H2 binding sites in the AR and INHA gene promoters were found. Transactivation studies showed that wild-type NR5A1/SF-1 regulates INHA and AR gene expression, while the NR5A1/SF-1 variant had decreased transcriptional ac-tivity. NR1H2 was found to regulate AR gene transcription; however, the NR1H2 variant showed normal activity. This study expands the NR5A1/SF-1 network of interacting partners while strengthening the hypothesis that the broad phenotype observed in 46,XY DSD individuals may be caused by oligogenic pathogenicity.