Type A Insulin Resistance Syndrome Due to a Pathogenic Variant in the INSR Gene

A woman in her 40s initially diagnosed with type 1 diabetes in 1994 exhibited an atypical 30-year metabolic course, characterised by fluctuating insulin sensitivity, prolonged insulin independence and later insulin resistance despite a non-obese phenotype.

Owing to the unusual clinical trajectory and a strong family history of young-onset diabetes, genetic testing identified a heterozygous pathogenic INSR mutation (p.M1180K), confirming Type A Insulin Resistance Syndrome (TAIRS).

Management evolved from insulin therapy to oral hypoglycaemic agents, including metformin and gliclazide alongside lifestyle modification resulting in partial glycaemic improvement.

This case underscores the diagnostic challenge of TAIRS, which is frequently misclassified as type 1 or type 2 diabetes and highlights the importance of early genetic evaluation and multidisciplinary care.