Connectomic and behavioural alterations in creatine transporter deficiency are partially normalized by gene therapy

Creatine transporter deficiency (CTD) is an X-linked disorder due to the loss of SLC6A8 gene and presenting with low brain creatine, intellectual disability, autistic-like behaviour and seizures. No treatments are available yet for CTD, and little is known about the brain circuit alterations underlying its pathological endophenotypes. Here, we tracked brain network and behavioural dysfunction in a murine model of CTD at two stages of disease progression. Functional MRI (fMRI) mapping revealed widespread disruption of brain connectivity in Slc6a8-knockout (KO) mice, with robust somatomotor hypoconnectivity in juvenile animals and weaker and more focal alterations of cortical and subcortical connectivity in adulthood. Notably, perinatal AAV-mediated expression of human SLC6A8 in Slc6a8-KO mice robustly prevented juvenile functional MRI (fMRI) hypoconnectivity, an effect accompanied by the regression of multiple translationally relevant phenotypes, including reduced stereotyped movements, improved declarative memory and increased body weight, all of which persisted into adulthood. However, early cognitive deficits, impairments in working memory and residual fMRI hypoconnectivity in adult mice were not ameliorated by gene therapy. Furthermore, significant cognitive impairments were observed in wild-type mice receiving gene therapy, highlighting a potential detrimental effect of ectopic expression of SLC6A8 in healthy brain circuits. Finally, multivariate modelling in adult mice revealed a basal forebrain network whose activity was associated with behavioural performance and modulated by brain creatine levels. This brain-behaviour relationship was disrupted in Slc6a8-KO mice. Our results document robust network disruption in CTD and demonstrate that CTD pathology can be partially alleviated by perinatal genetic expression of SLC6A8, providing a foundation for the future development of experimental therapies for this genetic disorder.