For families where a parent or sibling has type 1 diabetes, the wait to know can stretch for years. Blood tests and specialist visits become part of early childhood.
New research suggests the answer may already be taking shape in the baby's gut.
Infants at high genetic risk whose gut microbiome development plateaued early had about three times the risk of developing type 1 diabetes, or the immune attack that comes before it.
That finding comes from a study published September 21, 2026 in Nature Metabolism. It was led by researchers at Mass General Brigham, the Broad Institute of MIT and Harvard, and Harvard T.H. Chan School of Public Health.
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The team followed 887 children carrying high-risk genes and analyzed more than 12,000 stool samples during their first six years.
The gut microbiome is the community of bacteria and other microbes living in the intestines. In healthy babies it usually grows more diverse and mature during the first years of life.
Three paths for the infant gut
The researchers spotted three distinct patterns. Some children reached rich bacterial diversity within the first year. Others started slowly but caught up later. A third group started slowly and never progressed, and this early-plateaued group carried the higher risk.
Genetic risk alone did not tell the full story. The children's own genes influenced how strongly the microbiome pattern shaped their risk, particularly variants involved in how the immune system responds to microbes and viruses.
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The children came from a long-running international project called TEDDY, which has tracked babies at genetic risk for type 1 diabetes in the United States, Finland, Germany and Sweden.
Roughly 1.8 million children and adolescents live with type 1 diabetes worldwide, according to the International Diabetes Federation.
Limits and what could come next
The study is observational, meaning it can show associations but cannot prove that a slow-developing microbiome causes type 1 diabetes.
It also focused only on children already carrying high-risk genes, so the findings do not automatically extend to the general population.
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The researchers envision a future in which gut microbiome testing at early pediatrician visits helps flag which high-risk children need closer monitoring.
That could eventually open the door to microbiome-directed prevention such as dietary supplements. Similar work is already reshaping how researchers think about treating type 1 diabetes itself.
Families with type 1 diabetes in the household who worry about a young child can talk to their pediatrician about antibody screening, the standard early check for the immune signs that precede the disease.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.