New diagnostic criteria for Christianson syndrome may double the number of cases of the autism-like condition and provide the most definitive characterization of CS to date. A study in press in Annals of Neurology, which includes detailed behavioral, medical, and genetic observations of 14 boys with CS, quantifies its most frequent symptoms, such as moderate to severe intellectual disability, epilepsy, inability to walk and talk or difficulty doing so, and hyperactivity.
Senior author Eric Morrow, MD, PhD, assistant professor of biology and psychiatry and human behavior, says all boys in the study have a mutation on the SLC9A6 gene on the X chromosome that disables production of the protein NHE6, which is important for neurological development. The researchers found that girls can carry CS mutations on their X chromosomes, but they appear to be affected less severely or not at all. Morrow says SLC9A6 mutations—and therefore CS—may be a relatively common source of X-linked intellectual disability, with a potential frequency worldwide of more than 70,000 cases.
Studying the regression of walking and verbal skills among boys with CS could help researchers learn more about regressions in autism, says Morrow, who treats autism patients at the E.P. Bradley Hospital in East Providence. “If we could understand the biological mechanism that leads to that loss, and we can prevent it by developing a treatment, then these kids will remain further ahead,” he says. The new CS study, by uncovering mutations that lead to the disease, furthers that effort. “We can now study these different mutations and learn how this protein works by how it gets inactivated,” Morrow says. “All the different ways it gets inactivated can actually inform us about the different components of the protein that have an important function.”