When Diabetes Looks Like Type 1 but Isn't: A Rare Case of Misdiagnosis

In 2016, a 15-year-old girl was diagnosed with Type 1 diabetes and started insulin therapy. But something didn't add up. Her blood sugar control remained inconsistent despite treatment, raising questions about whether the initial diagnosis was correct. This prompted her doctors to take a closer look.

Over the next eight years, extensive testing was performed to understand what was really happening. In 2024, genetic testing finally revealed the answer: she didn't have Type 1 diabetes at all. Instead, she had a rare form of monogenic diabetes—a condition caused by mutations in a single gene or, in her case, multiple genes working together.

MODY stands for Maturity Onset Diabetes of the Young. It's a group of rare genetic forms of diabetes, each linked to mutations in specific genes that control how the pancreas makes and uses insulin. In this patient's case, the diabetes was 'digenic,' meaning it involved genetic variants in two different genes—PDX1 and HNF1B—rather than just one.

Both of these genes are crucial for pancreas development and for the cells that produce insulin. When they malfunction, the body's ability to produce insulin is compromised.

Initial genetic screening identified one variant in the HNF1A gene, which was initially thought to explain the diagnosis. However, more advanced genetic testing using next-generation sequencing uncovered a more complex picture: three genetic variants across two genes.

In the PDX1 gene, researchers found two variants located very close to each other. One changes an amino acid in the protein (p.Gly232Ser), while the other creates a premature stop signal that cuts the protein short (p.Glu233Ter). In the HNF1B gene, a third variant also produces a premature stop codon, resulting in a truncated, non-functional protein.

The combination of these variants—particularly the two that cause early protein termination—had not been previously documented in medical literature. Researchers concluded that all three variants likely contributed to the patient's diabetes.

This case illustrates an important point: not all diabetes that appears in childhood is Type 1 diabetes. When a patient's response to standard diabetes treatment is unusual or inconsistent, genetic testing can reveal the true cause and open the door to more targeted treatment approaches.

For patients and families, this underscores the value of comprehensive evaluation when diabetes doesn't follow the expected pattern. Identifying the genetic basis of diabetes can change how the condition is managed and monitored over time.

Source: Molecular genetics & genomic medicine. 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.