ASD is a developmental disability characterized by social, communication and behavioral challenges.
The researchers, from the University of Cambridge in the UK, publish their findings in the journal Cerebral Cortex.
Autism spectrum disorder (ASD) is a developmental disability - that includes Asperger Syndrome - causing critical social, communication and behavioral obstacles. According to the Centers for Disease Control and Prevention (CDC), ASD occurs in about 1 in 68 children in the US, and it is five times more common in boys than girls.
Appearing during early childhood, ASD does not typically carry with it identifying physical characteristics. However, those with the condition may communicate, behave and learn in ways that are different from the majority of other people.
Because there are no medical tests for doctors to employ when diagnosing ASD, they often assess the child's behavior and development.
Lead author Dr. Meng-Chuan Lai, of the Cambridge Autism Research Centre, says:
"Although people with autism share many features, they also have a number of key differences. Language development and ability is one major source of variation within autism. This new study will help us understand the substantial variety within the umbrella category of 'autism spectrum.'"
Smaller brain volumes in men with language delay
To conduct their study, the research team studied 80 adult men with autism - 38 of whom had delayed language onset - who were part of the Medical Research Council Autism Imaging Multicentre Study (AIMS).
- In the US, ASD affects around 1 in 68 children
- ASD costs at least $17,000 more per year per child, compared with those without ASD
- Many children do not receive a final diagnosis until they are older than age 2, which means children with ASD may not get the early help they need.
Delayed language onset occurs when a child's first meaningful words come out after 24 months of age, or when their first phrase occurs after 33 months.
In the men who had delayed language onset, the researchers found that certain key regions of the brain had smaller volumes, including the temporal lobe, insula and ventral basal ganglia. Additionally, these men also had larger brainstem structures, compared with those who did not have delayed language onset.
The team also observed a link between current language function and a specific pattern of grey and white matter volume changes in key brain regions, including the temporal, frontal and cerebellar structures.
Dr. Lai says their study shows how the brains of autistic men differs, based on early language development and current language function, adding that this "suggests there are potentially long-lasting effects of delayed language onset on the brain in autism."
However, when asked about whether their observations could suggest cause or effect, Dr. Lai told Medical News Today:
"This is a correlation study of childhood development history to current neuroanatomy in adulthood so cannot directly test for causal relationship, which requires longitudinal dataset followed up from early childhood. We have not conducted studies in relation to this aspect now but are aware of longitudinal projects that may be potentially able to address this and related questions."
He adds: "We need to move beyond investigating average differences in individuals with and without autism, and move towards identifying key dimensions of individual differences within the spectrum."
Autism: a single spectrum or discrete subgroups?
The researchers note that the American Psychiatric Association removed Asperger Syndrome as a separate diagnosis from its diagnostic manual (DSM-5) last year, classifying it under ASD. This was a change that proved controversial within the medical community.
"This new study shows that a key feature of Asperger Syndrome, the absence of language delay, leaves a long-lasting neurobiological signature in the brain," says senior author Prof. Simon Baron-Cohen. "Although we support the view that autism lies on a spectrum, subgroups based on developmental characteristics, such as Asperger Syndrome, warrant further study."
Dr. Lai adds, "When asking: 'Is autism a single spectrum or are there discrete subgroups?' - the answer may be both."
Earlier today, MNT reported on a study that suggested maternal iron intake is linked to offspring autism risk, and another recent study explored how sex hormones influence autism risk.