In the late diagnosis of autism spectrum disorder (ASD), a risk factor that has been repeatedly identified is a low birth weight or low gestational age at the time of birth. The odds of a child less than 3 years of age being diagnosed with ASD are greater for infants born preterm, before 37 gestational weeks, or with a low birth weight when compared with their full-term or normal-weight counterparts. Despite the large amount of evidence accumulating that premature singleton births provide a higher risk of developing ASD, no large-scale neuroimaging has been performed to investigate the link. Now, a study from researchers at the Karolinska Institutet has shown that extremely premature babies run a much higher risk of developing autism in later childhood, with differences in the neonate period of brain development being noted. The team state that their findings suggest that environmental factors can lead to autism.
Previous studies show associations between low birth weight and preterm delivery and the later development of autism. One reason for this may be that some of the children born preterm or with a low birth weight have other medical conditions that also predispose them to autism. Another theory that has been proposed is that children from a non-singleton gestation have an increased risk of autism and are also more likely to have a low birth weight or preterm birth. However, data reviewing multiple births and a diagnosis of ASD by 8 years of age found no association between the autism and multiple births. Thus, a definitive link between low-weight, preterm birth and the development of autism remains elusive. The current study supports previous findings via neuroimaging indicating that birth weight and complications can increase the risk of autism.
The current study examined over 100 babies who had been born extremely prematurely, before week 27; the beginning of the third trimester. With the parents’ permission the lab studied the growth of the babies’ brains using magnetic resonance imaging during the neonate period, and then screened the children for autistic features when they had reached the age of six. Results show that almost 30% of the extremely preterm-born children had developed ASD symptoms; amongst children born after full-term pregnancy, the corresponding figure is 1%.
Data findings show that it was more common in the group of children who had experienced complications and stress during the neonate period, such as surgery, to develop ASD. The lab note that already in the neonatal period, long before the children had manifested signs of autism, differences could be observed between the extremely preterm babies who went on to develop ASD and those who did not. They go on to add that they observed diminished growth of the parts of the brain involved in social contact, empathy and language acquisition in those extremely preterm infants who went on to develop ASD.
The team surmise that their findings show that downstream environmental factors, as well as upstream genetics, can also cause autism. They go on to add that the brain grows best in the womb, and if the developmental environment changes too early, it can disrupt the organisation of cerebral networks. For the future, the researchers state that with new therapeutic regimes to stimulate the development of such babies and avoid stress, maybe the global medical community can reduce the risk of their developing ASD.
Source: Karolinska University Hospital