A team of researchers of the "http://www.vhir.org/larecerca/grupsrecerca/ca_grups_equip.asp?Idioma=en&mv1=2&mv2=1&mh1=2&mh2=1&mh3=1&mh4=0&ms=0&area=7&grup=3&menu=3" Immunology group at Vall d'Hebron Institute of Research (VHIR) have discovered that an autoimmune regulator protein, called AIRE, is less expressed in individuals with Down Syndrome. This finding explains why the people with this syndrome have more predisposition to suffer autoimmune diseases.For the study, published in "http://www.jimmunol.org/content/193/8/3872.long" the Journal of Immunology, VHIR researchers used the major collection of thymus samples collected until now. Specifically, they analyzed samples from 19 individuals with Down Syndrome and congenital heart disease, collected since 1995 at the Pediatric Surgery unit of the Vall d'Hebron University Hospital. All thymus were removed following cardiac surgery because in this type of interventions the organ can't be reintroduced. All samples were compared with the samples of patients with congenital heart disease but without Down Syndrome. The AIRE protein is codified on chromosome 21, which is tripled in individuals with Down Syndrome. Despite having three copies of the chromosome, they have more predisposition to suffer autoimmune diseases such as diabetes, celiac disease and hypothyroidism. To determine which is the role of AIRE in these individuals, Vall d'Hebron researchers analyzed its expression in the thymus."Contrary to what we expected, we saw that in patients with Down Syndrome the protein is expressed in lower levels that in the rest of the people", assured Dr. Roger Colobran, main author of the study. As a consequence, the expression of the specific genes that depend on this protein is also reduced, and this produces the central tolerance failure that takes place in the thymus.The origin of many autoimmune diseases is in the thymus, which is the organ of the immune system where the T lymphocytes, that coordinate the immune response, are developed. AIRE controls the mechanism that educates the T lymphocytes to attack external organisms such as virus, bacteria, fungus or parasites, instead of the own cells of the body. However, when this protein is less expressed, there is a central tolerance failure and T cells attack the own cells, which can cause ultimately an autoimmune disease.