The most common genetic cause of the brain diseases frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) is a mutation in the C9orf72 gene. Researchers have demonstrated that if an affected parent passes on this mutation, the children will be affected at a younger age (than the parent). There are no indications that the disease progresses more quickly. These results were published JAMA Neurology.
After Alzheimer’s disease, FTD is the most common form of dementia in young patients. A fraction of FTD patients show symptoms consistent with ALS, a disease in which the nerve cells that control the muscles in the brain and spinal cord are affected. This causes ALS patients to progressively lose muscle mass, resulting in loss of strength in the limbs and problems with speaking, swallowing, and breathing. ALS is more common without FTD symptoms.
The mutation in C9orf72 consists of a repetition of a short DNA sequence GGGGCC which can expand in patients up to several thousands of repetitions. It is not yet known why some patients get FTD and others ALS.
The age at first presentation of disease symptoms ranges in patients from 29 to 82 years, even in patients from the same family. Until recently, there was no explanation for this high variability. The researchers demonstrated in 2016 that the age of onset is determined by the number of GGGGCC repeats: the more repetitions, the earlier the age of onset. In C9orf72 families in which the affected parent had a late age of onset and their affected children an earlier age of onset, the researchers provided evidence that the GGGGCC repeat in the C9orf72 gene expanded from a short sequence of repeats (less than 200 repeats) to a long one (more than a thousand).
In the new study, the researchers looked at the age of onset across multiple generations. They found that in successive generations of C9orf72 families, the age of onset was markedly different. According to the researchers, most of the patients from the later generations — i.e., the children or grandchildren of the oldest subjects – showed disease symptoms at a younger age, even as the disease was shown to progress no more quickly than in older generations.
Paper: “Children of patients with C9orf72 mutations are at a greater risk of frontotemporal dementia or ALS at a younger age”
Reprinted from materials provided by VIB – Flander Interuniversity Institute for Institute for biotechnology.