Scientists investigating developmental disability have come to the conclusion that these disabilities, mental illnesses, and neurological disease are all aspects of the same type of disorder. Under current models, the three types of condition are perceived as clinically distinct, meaning that they are treated as different and unrelated disorders, with different causes, different prognoses, and different courses of treatment. However, there is a growing body of opinion that, rather than being distinct, these conditions exist along a continuum, and are all fundamentally linked.
"Recent genetic studies conducted in thousands of individuals have shown that identical genetic mutations are shared among neurodevelopmental disorders that are thought to be clinically distinct," said autism researcher Andres Moreno De Luca, M.D., a co-author of a recent article laying out this new model, in a statement. "What we have seen over the past few years is that genetic mutations that were initially found in individuals with one disorder, such as intellectual disability or autism, are then identified in people with an apparently different condition like schizophrenia, epilepsy, or bipolar disorder."
This model means that the research techniques and approaches used for mental illnesses such as schizophrenia can also be brought to bear on intellectual disabilities. It means the treatment approaches used for mental illnesses may also have application for neurological disorders thought to be untreatable. Perhaps more importantly, demonstrating an underlying genetic or biological abnormality linking all these conditions could go a long way towards eroding the stigma attached to them, a stigma which in some cases does more to impede people in society than the conditions themselves.
As for what this underlying cause is, this remains unclear. However, recent studies have found a link between treatments for male infertility and both developmental issues and autism in the resultant offspring. The risk was associated with an in vitro technique called intracytoplasmic sperm injection, in which a miniature syringe is used to inject a single sperm cell directly into an ovum under a microscope. This procedure is reserved for severe cases of male infertility.