Minor physical anomalies in autism spectrum disorders and velocardiofacial syndrome

Abstract

Minor physical anomalies (MPA) are mild congenital malformations in external physical abnormalities that are observed in neurodevelopmental disorders such as velocardiofacial syndrome (more commonly known as 22q11.2 deletion syndrome), autism and schizophrenia. It has been reported that about three-quarters of MPAs can be found in the craniofacial region, such as low-seated ears, high-steepled palate, altered interorbital distance. Furthermore, both eye and brain development are tightly linked, and interorbital distance and optic chiasmic angle in adulthood are perinatally fixed. Therefore my study investigated MPAs of the optic system in two neurodevelopmental disorders, 22q11.2 deletion syndrome and autism spectrum disorders (ASD). The four selected MPAs included 1) inter-orbital distance, 2) the optic chiasmic angle, 3) anterior extension of optic nerves ‘a’, and 4) posterior extension of optic nerves ‘b’. They were investigated in two individual studies, the first comprising 17 adults with ASD and 21 controls while the second comprised 27 adults with 22q11.2 deletion syndrome and 28 controls. Their MRI scans were analysed with respect to the MPAs. The main finding was that adults with ASD had significantly larger total brain volume which was positively correlated with the anterior extension of optic nerves ‘a’, but not the other optical MPAs. This suggested that the larger brain volume was more related to frontal brain enlargement. As no relevant significant results were obtained in the controls nor adults with 22q11.2 deletion syndrome, such finding appears pertinent to ASD adults, rather than that to a genetic neurodevelopmental disorder. However, this finding is only preliminary, and other neurodevelopmental disorders should be included for comparison with ASD and healthy controls. The use of MRI appears to be a feasible tool to assess MPAs. Future work will focus on whether these observations can be replicated across the life-span by evaluating these parameters in children with ASD, as well as adults with other neurodevelopmental disorders.