Blood Tests Can Identify Which Relatives of T1D Patients Face Highest Disease Risk

Type 1 diabetes runs in families. First-degree relatives—siblings and children—of people with T1D have a significantly higher chance of developing the condition themselves. But risk varies widely among family members, and until now, there hasn't been a clear way to identify which relatives face the greatest danger.

Beyond Type 1 diabetes, relatives also carry elevated risk for other autoimmune diseases, particularly celiac disease and autoimmune thyroid disease. Understanding these connections could help families and doctors prepare for potential health changes.

Researchers followed 1,427 Danish siblings of children newly diagnosed with Type 1 diabetes, beginning between 1997 and 2010. They collected blood samples and DNA, then tracked participants' health through national medical registries until 2024—providing up to 27 years of follow-up data.

The team tested each sibling's blood for four autoantibodies linked to Type 1 diabetes, one marker for celiac disease, and one for autoimmune thyroid disease. They also calculated each person's genetic risk score based on genes known to influence T1D susceptibility.

Among 1,417 siblings who provided usable samples, 7.8% tested positive for islet autoantibodies—the hallmark of T1D-related autoimmunity. Of those, 4.6% carried multiple autoantibodies, which proved to be the strongest predictor of future disease.

The study's risk calculations were striking. Siblings with no autoantibodies developed Type 1 diabetes at a rate of 0.11 cases per 100 person-years. Those with a single autoantibody increased to 2.46 cases per 100 person-years—a 22-fold jump. Siblings carrying multiple autoantibodies reached 8.10 cases per 100 person-years—a 73-fold increase compared to autoantibody-negative relatives.

For celiac disease, siblings positive for tissue transglutaminase (tTGA) autoantibodies developed the condition at 1.97 cases per 100 person-years. For autoimmune thyroid disease, those with thyroid peroxidase (TPOA) autoantibodies developed it at 0.69 cases per 100 person-years.

Genetic background also played a role. Siblings carrying certain HLA gene combinations—specifically DR3/DR4 haplotypes—were significantly more likely to test positive for autoantibodies in the first place.

The key finding is that a single blood test screening for autoantibodies, combined with genetic risk scoring, can reliably separate siblings into risk groups years or even decades before disease develops. This kind of precision could help families understand their own health trajectories and work with their doctors on monitoring strategies.

The study did not examine whether early detection or any specific interventions could prevent or delay disease onset in these at-risk relatives. That remains an important area for future research. But having accurate risk information is an essential first step.

Source: Diabetes, obesity & metabolism. 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.