The TRIO-related intellectual disability syndrome is caused by a mutation in the gene TRIO. If you think about our DNA as the letters of the alphabet, the mutation is typically a change of a single letter. This change causes a misspelling of the “words” made up by the alphabet. In this case, the information encoded by this gene is disrupted and non-readable. The gene and the protein it produces seem to play an important role in the developing brain.
In many of the cases, the TRIO mutation that is found in the affected child is neither present in the father, nor the mother. This is considered a “de novo” mutation. In that case, the chances for future children to be affected with this syndrome are considered to be very low, but appear to exceed that of the general population.
However, each child of an affected individual has a 50% chance of being affected dependent on whether or not he or she inherits the mutated or normal copy of the gene from the affected parent. Given that affected people may present a borderline-normal cognitive functioning or a mild degree of intellectual disability, it is not surprising that they may present within different generations in the same family (eg. a parent and some of his/her children).
Prenatal genetic counselling can be offered following confirmation of the diagnosis within a family.