Nadia Tinto

Summary Insulin receptor gene ( INSR ) mutations are a relatively rare and diverse cause of insulin resistance (IR), typically associated with a lean phenotype. However, we present a unique case of severe obesity and Type A severe IR syndrome in a patient with a heterozygous mutation of the INSR gene. Next Generation Sequencing (NGS) analysis was conducted to identify the genetic variant. A 16‐year‐old girl with severe obesity (BMI‐SDS +2.79) exhibited markedly elevated basal insulin levels (>800 mcU/L). Despite obesity being a known cause of hyperinsulinism, further investigation was pursued due to the severity of hyperinsulinaemia. A heterozygous nucleotide variant at the donor splicing site of intron 13 (c.2682 + 1G > A) of the INSR gene was identified. This mutation was also present in the proband's normal‐weight mother and her two younger brothers with obesity. Metformin treatment provided limited benefits, but subsequent liraglutide therapy resulted in weight loss and decreased IR 3 months after initiation. Our findings suggest that obesity can exacerbate hyperinsulinaemia in individuals with an INSR gene mutation. Although INSR signalling defects play a minor role in the aetiology of IR, they should still be considered in the diagnostic pathway, particularly in severe phenotypes. Clinicians should not overlook the possibility of genetic causes in patients with obesity and IR, as they may require personalized management approaches.

Background: Next-generation sequencing (NGS) technology is revolutionizing diagnostic screening for mitochondrial diseases (MDs). Moreover, an investigation by NGS still requires analyzing the mitochondrial genome and nuclear genes separately, with limitations in terms of time and costs. We describe the validation and implementation of a custom blended MITOchondrial-NUCLEAR (MITO-NUCLEAR) assay for the simultaneous identification of genetic variants both in whole mtDNA and in nuclear genes included in a clinic exome panel. Furthermore, the MITO-NUCLEAR assay, implemented in our diagnostic process, has allowed us to arrive at a molecular diagnosis in a young patient. Methods: Massive sequencing strategy was applied for the validation experiments, performed using multiple tissues (blood, buccal swab, fresh tissue, tissue from slide, and formalin-fixed paraffin-embedded tissue section) and two different blend-in ratios of the mitochondrial probes: nuclear probes; 1:900 and 1:300. Results: Data suggested that 1:300 was the optimal probe dilution, where 100% of the mtDNA was covered at least 3000×, the median coverage was >5000×, and 93.84% of nuclear regions were covered at least 100×. Conclusions: Our custom Agilent SureSelect MITO-NUCLEAR panel provides a potential “one-step” investigation that may be applied to both research and genetic diagnosis of MDs, allowing the simultaneous discovery of nuclear and mitochondrial mutations.