Delineating the Molecular Spectrum and the Clinical, Imaging and Neuronal Phenotype of Chopra-Amiel-Gordon Syndrome (CAGS NHS)

Heterozygous loss of function variants in ANKRD17 were recently implicated in a newly-identified rare intellectual disability syndrome. In an international collaborative effort spanning 4 years, the mutational and phenotypic spectrum of 34 patients were described (Chopra et al AJHG 2021). The core phenotypic features of this syndrome were shown to be intellectual disability, particularly affecting speech, and shared dysmorphic features. Variably present neurodevelopmental features were epilepsy /abnormal EEG, autism spectrum disorder, gait / balance difficulties and neuroimaging abnormalities. Extra-neurological features include growth delay, renal anomalies, hypermobility, pigmentary lesions and feeding problems. All variants were identified on whole exome or whole genome sequencing, and most were shown to be de novo and truncating, although some patients harbored missense variants particularly in highly conserved ankyrin repeat domains. While this initial project presented compelling evidence for a novel gene-disease relationship and established the key phenotypic features of this new disorder, there were limitations to this work. The neurodevelopmental profile and MRI findings were ascertained through physician report only rather than independent standardized assessment. Intriguingly, while it was observed that expressive language delay was more markedly affected than other developmental parameters, this observation was not validated with standardized patient evaluation. Currently, the impact of ANKRD17 haploinsufficiency on human neuronal morphology / excitability, and in turn, the correlation of this neuronal phenotype to the clinical neurodevelopmental profile is unknown. With this study, the investigators plan to deeply characterize the longitudinal spectrum of clinical, neuroimaging and neuronal cellular features of this disorder, pairing preclinical with clinical science. The robust annual systematic evaluation of patients who are known or suspected to have this condition will lead to a better understanding of the true phenotypic spectrum and correlations to genotype. The inclusion of patients with ANKRD17 VUS and/or suspected to have CAGS, in particular, may expand the phenotypic and genotypic spectrum of the condition, and clarify diagnoses for these participants. The generation of patient-specific iPSC lines and isogenic controls will allow for future projects to generate neuronal populations from clinically characterized patients, which will bridge the knowledge gap on the biological underpinnings of the disorder and potentially lead to biomarkers that reflect specific disrupted neurodevelopmental pathways.