The relationship among psychiatric disorders is very narrow, at least from the molecular level. That is what has been detected by an international research about brain disorders. The genetic variables were analysed in over 800,000 people (both patients and healthy people) from all over the world. The result showed that psychiatric disorders such as schizophrenia, autism, bipolar disorder, depression and attention deficit hyperactivity disorder (ADHD) all share a common genetic basis. However, even though all these disorders occur in the brain, the relationship among psychiatric disorders are quite different from those identified in neurological diseases. The results of this scientific research, publish in Science, revealed that neurological diseases such as Alzheimer’s, ischemic stroke, multiple sclerosis and Parkinson’s disease do not share similar genetic bases, nor are they genetically related to psychiatric disorders (e.g. depression).
In fact, medical doctors had already predicted such results based on their every-day consultations with patients.They could not understand, for example, why some of their patients with depression would develop anxiety and then be diagnosed with ADHD. “At the clinical level, we could observe several coincidences or comorbidities. hence the decision to use the pre-existing genetic data of several brain diseases to try to find if there was any genetic relationship among them.”, explains Dr. Bru Cormand, from the Institute of Biomedicine at the University of Barcelona (UB), along with 500 other researches who participated in the macro-study. In a combined effort, hundreds of scientists from all over the world analysed the genetic bases of 25 psychiatric and neurological disorders using the genome of 215,683 patients and 657,164 people used as “control” (not sufferers from any psychological or neurological disorders).
The researchers looked at millions of genetic variations in every person who participated in the study and they found a strong genetic relationship among some psychiatric disorders and huge differences among neurological diseases.
The results show that schizophrenia and depression, for instance, have a partially common genetic basis to the other psychiatric disorders that were analysed. Furthermore, schizophrenia, bipolar disorder, depression and ADHD share around 40% of a common genetic basis. “Anorexia and obsessive compulsive disorder (OCD) also share a strong genetic relationship, above 50%. Autism is genetically distant from most of the psychiatric disorders, except for schizophrenia”, says Dr. Cormand.
Neurological disorders, on the other hand, hardly share any genetic basis – except for Parkinson’s disease and multiple sclerosis, which are 45% genetically correlated to a type of epilepsy. Neither are neurological diseases related to psychiatric disorders.
The only genetic coincidence between a psychiatric disorder and a neurological problem was detected between migraine and ADHD. “We already suspected this result because of what we’ve beee observing in several cases of patients with ADHD and migraine. Now we see the puzzle pieces that these disorders share”, says Dr. Josep Antoni Ramos Quiroga, head psychiatrist at the Psychiatric Hospital Vall d’Hebron, in Barcelona, and also a collaborator in the study. Dr. Cormand adds that migraine shares about 20% of its genetic basis with Tourett syndrome, 25% with ADHD and 30% with depression.
However, the researchers did not limit this macro-study to genetic analyses only. They also included in the analyses other cognitive parameters such as school performance, every-day habits such as smoking, eating habits, physical exercise levels and obesity, and certain personality traits (emotional instability, for example) to establish the coincidences among the pathologies.
“Genes have a lot to do with the origin of these disorders, but we understand that the environment shapes how genes express in the human body. That is why we studied other quantitative variables and we observed that ADHD, for example, is related to fewer years of schooling, an increase in smoking frequency, to weight gain and obesity.” says Dr. Ramos Quiroga.
The researchers agree that these are all very complex disorders that involve very complex genetic bases. The next step is to analyse gene by gene to find specific alterations in each pathology. “We have a lot of information on the genetic alterations of these pathologies that take place in the population. These genes, present in healthy people, can lead to the onset of psychological or neurological diseases depending on how they are combined. We are currently studying the rare variations that we only find in patients”, says Dr. Cormand.
Dr. Ramos Quiroga also believes that it’s crucial to investigate other “pieces of the puzzle” to try to create therapeutic procedures to modify them. Additionally, according to the psychiatrist, this study opens the doors to prevention of brain disorders.