The Canary Islands have the highest incidence of type 1 diabetes mellitus in children in Spain and one of the highest in Europe. Studies carried out to date place the range between 30 and 35 cases per 100,000 boys and girls per year, a figure which practically doubles the average for the entire national territory (17/100,000). The reasons for this marked difference are not entirely clear. According to experts, the development of this autoimmune disease is influenced by environmental factors, such as exposure to certain foods from an early age, vitamin D levels or suffering from viral infections, but also a genetic predisposition .
A recently published article in BMC Pediatrics, an open access journal that publishes peer-reviewed studies and part of the Springer Nature publishing house, offers a “plausible, evidence-based hypothesis with sufficient weight” to explain, at least in part, this island particularity: the North African genetic load.
Pediatric endocrinologist Yeray Nóvoa, member of the Canary Islands Pediatric Research Association, is the main author of an article signed by thirteen other specialists from different branches of health. The study hypothesis is that “a common genetic background”, resulting from the migration of Arab and North African populations and the resulting genetic mixing, “could help explain” the higher incidence of diabetes in type 1 in children (boys and girls up to 14 years old). in the “Arab, North African, Sardinian and Canarian” populations.
The starting point are the studies carried out by Carlos Flores, doctor from the University of La Laguna, on the genetic composition of the population of the Canary Islands, unique in Europe. The islands’ current inhabitants are “a historical mix of Western Europeans, North Africans, and sub-Saharan Africans.” An article published at the end of 2022 in the journal Scientific Reports, from the Nature group, estimated between 17 and 23% of the imprint of North Africa in the DNA of contemporary canaries. This is the particularity of the archipelago. No other European region has such a high proportion of this ancestry. The influence of the Iberian Peninsula (mainly Galicia and Portugal) exceeds 70% and that of the Sub-Saharan Peninsula is around 3%. These studies also confirmed that the last admixture event occurred approximately fourteen generations ago.
The study published in September analyzes the DNA of 309 children diagnosed with type 1 diabetes in Gran Canaria and 222 without the disease. The main author of the article explains that most of the genes linked to this pathology are associated with the immune system. The research focuses on a genomic region, called HLA, which accounts for “up to 50% of the genetic risk” of type 1 diabetes mellitus.
Nóvoa points out that in this region there are genes that predispose to the disease and others that protect against it. The main finding of the study is the low prevalence in the entire child population of Gran Canaria (and not just those with type 1 diabetes) of protective molecules called HLA-DQB1 with aspartic acid in position 57. In the control population (minors without diabetes), 58% of the genes analyzed were devoid of this amino acid with a protective effect against the disease. This data is similar to other populations that also have high rates of diabetes.
“Type 1 diabetes has a genetic basis that does not follow classical Mendelian laws, that is, it does not follow the direct inheritance model in which, if you have one or two specific genes, you suffer from the disease. In diabetes, there is a genetic predisposition. This means that there are people who have this genetic load and develop diabetes, and others who have this genetic load and do not develop it. In other words, genetics does not predict with 100% certainty that you will develop the disease, but it makes it more likely,” explains Nóvoa.
The study establishes several correlations. First, the higher incidence of the disease in the Canary Islands and the low prevalence of this protective gene. On the other hand, there are regions of the genome of the island population in which North African ancestry has “a lot of weight”. And among them, with a charge of around 50%, is HLA. Another piece of information reinforces the hypothesis. The map of countries with the highest incidence of type 1 diabetes in the world includes, for example, Algeria or Tunisia, as well as other regions of the Arabian Peninsula or Sardinia. In this “migratory extension”, in this corridor going from the Arabian Peninsula to North Africa, Sardinia and the Canary Islands, we see a higher incidence of the disease.
The pediatrician emphasizes that there are no studies on the incidence of the disease in Morocco, but that there is indirect data. For example, people from this country who reside in Spain or Italy. And a high incidence was also detected. Novoa insists. With current knowledge and evidence, we cannot yet speak of a causal relationship, but we can speak of a correlation. The results of the study pave the way for continued exploration, with larger-scale research, of the role of these genes in the origin of type 1 diabetes. “This article does not explain everything, it This is why we must continue to explore this issue further. genetic study to better understand the differences,” he says. Further research into the genetics of type 1 diabetes in the Canary Islands is currently being carried out through collaborative studies involving hospitals from most of the islands.
“The paradigm is changing”
Nóvoa explains that the paradigm for treating the disease is changing. “We are not curing type 1 diabetes, but we are ensuring that people with diabetes can survive, yes, with an increasingly high quality of life. When we manage to detect it at an early stage, when autoimmune activity begins to appear, without producing an increase in blood sugar, we are already beginning to have treatments capable of delaying its appearance by two or three years. . For this reason, continues pediatric endocrinology, population screening strategies are beginning to be considered to detect people who are likely to develop it in the future.
Type 1 diabetes is an autoimmune disease. This happens because the body’s defensive cells “destroy” those that produce insulin. This hormone allows sugar to pass from the blood into cells to be used as an energy source. It is the most common type of diabetes in children and its mechanisms are different from type 2. The difference is that in the latter “there is no autoimmune destruction, but rather resistance to insulin action, especially linked to obesity, with excess adipose tissue, making it more difficult for insulin to act to lower sugar levels, overloading the pancreas so much that it can no longer respond.
The mechanisms are different and so are the causes. In type 2 diabetes, there is a clear association between disease onset and obesity, linked to lower socioeconomic levels. In studies of type 1 diabetes mellitus, we often talk about environmental and genetic conditions, but at the moment there is not “100% certainty about the factors that actually predispose” to suffering from it.
“In autoimmune diseases, we talk about hygiene theory. It has been observed that people from developing countries, where the incidence of autoimmune diseases is normally low, who emigrate to more developed countries, begin to exhibit autoimmune diseases with rates similar to those in countries adoption. It is believed that the low exposure to infectious diseases during childhood in developed countries makes the development of the immune system different and predisposes to more autoimmune diseases,” explains the pediatrician.
“We are trying to deepen our knowledge of the mechanisms of diabetes in the Canary Islands. This could allow us, in the not too distant future, to more easily develop screening strategies aimed at our population, thus achieving greater efficiency,” concludes Nóvoa.
