When Type 1 Diabetes Isn't Type 1: The Story of a Rare Genetic Misdiagnosis

In 1994, a woman in her 40s received a diagnosis of type 1 diabetes. But over the next three decades, something unusual happened. Instead of following the typical course of type 1 diabetes, her condition shifted and changed in ways that didn't match the disease her doctors had identified.

She experienced periods of insulin independence—times when she didn't need insulin injections—despite having been diagnosed with an autoimmune condition that typically requires lifelong insulin therapy. Later, she developed insulin resistance, a hallmark of type 2 diabetes. Yet she remained lean and didn't show the weight patterns usually associated with insulin resistance.

This 30-year mismatch between her diagnosis and her actual medical journey pointed to something else entirely.

Puzzled by her unusual trajectory and aware of a strong family history of early-onset diabetes, her medical team pursued genetic testing. The results revealed a pathogenic variant in the INSR gene—a mutation called p.M1180K that she inherited from one parent.

This genetic change causes Type A Insulin Resistance Syndrome (TAIRS), a rare condition distinct from both type 1 and type 2 diabetes. It affects how the body's insulin receptors function, leading to profound insulin resistance that can mimic other forms of diabetes but requires different treatment approaches.

TAIRS is frequently misclassified as type 1 or type 2 diabetes because its symptoms can overlap with both conditions. A person might present with high blood sugar, require insulin, or show signs of insulin resistance—all features that fit the more common diabetes diagnoses.

Without genetic testing, these cases can go unrecognized for years or decades. Patients may receive treatments designed for type 1 or type 2 diabetes that don't address their actual underlying condition.

Once her diagnosis was confirmed, this patient's treatment plan changed. Rather than continuing insulin therapy alone, her doctors added oral medications including metformin and gliclazide, supported by lifestyle modifications. This multidisciplinary approach produced partial improvement in her blood sugar control.

Her case underscores an important lesson: when diabetes doesn't follow the expected pattern—unusual insulin needs, unexpected insulin resistance, or a strong family history of young-onset diabetes—genetic evaluation may reveal a different diagnosis entirely. Identifying the true underlying condition opens the door to more targeted and effective care.

Source: Irish medical journal. Evidence type: PubMed indexed literature. Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.