The risk of developing type 1 diabetes
Author: Dr Sorin Ioacara | Last update: 30 August 2020
Can type 1 diabetes (T1DM) occur at any age? The answer is definitely yes. Type 1 diabetes is responsible for most cases of diabetes in children. The peak incidence is around the age of 14. After the age of 18, only 10% of cases of diabetes are type 1.
In reality, the percentage of type 1 diabetes in adults is slightly higher, probably 15%. What is surprising, however, is the fact that type 1 diabetes can appear even after the age of 70. The risk of developing type 1 diabetes varies widely in the general population.
Most cases of type 2 diabetes that start at the age of 40 and end up being treated with multiple injections of insulin after only five years of evolution are type 1 diabetes.
The risk of type 1 diabetes without a family history
In 90% of cases, type 1 diabetes occurs in a person without a family history of type 1 diabetes. Only 10% of new type 1 diabetes cases have someone in the family also affected by type 1 diabetes. Lifetime type 1 diabetes risk is about 1%. Thus, out of 100 newborns, one will develop type 1 diabetes during their lifetime, sometimes even after the age of 70 years. Out of 1,000 newborns, four will develop type 1 diabetes by the age of 20. Besides, another six will join the diabetes family between 20 and 70 years old.
The incidence is the number of new cases in a year for 100,000 inhabitants of all ages. The highest incidence of type 1 diabetes is in Finland. Here, this rate reaches 60 cases per 100,000 inhabitants. The incidence of type 1 diabetes is generally high in all Nordic countries.
In Romania, the incidence of type 1 diabetes is five times lower. It is about 12 per 100,000 inhabitants. The most affected age group is 10-14 years. Here, the incidence is about 18 per 100,000 inhabitants. The incidence of type 1 diabetes has doubled in Romania in the last 20 years.
The highest increase is registered in the age group 0-4 years. Most countries where such records exist reported similar increases. This dynamic of incidence suggests that the origin of type 1 diabetes is primarily related to environmental factors. Genetic causes have only a secondary role.
The much higher percentage of at-risk HLA gene carriers explains the increased incidence of type 1 diabetes in countries located in the north of the northern hemisphere (including Canada). For comparison, the incidence of type 1 diabetes in Japan is 2 cases per 100,000 inhabitants. Most Asian countries have this low incidence.
In countries where there are several races at the same time, the white race will have a much higher incidence of type 1 diabetes.
Prevalence is the number of cases with a particular disease per 100 inhabitants. It is about the percentage of the population that suffers from that disease. The prevalence of type 1 diabetes answers the following question. “If we took 100 people of any age from the street in how many of them would we find the disease?”
The prevalence of type 1 diabetes is 0.4%. This means that if we randomly investigate 1,000 people, we will find four with type 1 diabetes.
The risk of type 1 diabetes when a parent is affected
If a parent has type 1 diabetes, the risk of developing type 1 diabetes in the child is about 2% if the mother has diabetes and 6% for the father. If both parents’ age at onset is over 25, these differences are no longer here. Consecutively, the risk becomes 4% in this case. The risk for children is higher if the age at onset of the affected parent is ≤10 years.
The risk of diabetes in children increases significantly if both parents are affected. It reaches up to 30%. The risk increases if there is a history of type 1 diabetes in one of the parents of the affected parent. In other words, if a child’s grandfather is also affected.
The risk of type 1 diabetes when a sister or brother is affected
In the case of twins, when one child is affected, the other has a 50% risk of type 1 diabetes if it is genetically identical. Genetically identical means that they had the same placenta. The risk decreases to 10% if the twins are genetically different. In other words, they had separate placentas. The same risk of 10% applies to sisters or brothers from different pregnancies.
The risk for first-degree relatives increases with a younger age at onset of the affected child. This risk will increase further if the age of the father without diabetes is higher. Also, the risk is slightly higher for the brothers of the affected child compared to his sisters.
When the affected child has HLA risk genes (DR3 / DR4), the risk for siblings who also have the same HLA genes increases to 15%. Without both of these risk genes, their risk drops to 6%. The onset of type 1 diabetes in a child increases the risk of diabetes for his parents ten times.