The goal of this observational study is to learn about the neurological and cardiological phenotype of patients with resistance to thyroid hormone (RTH) syndromes beta and alpha (RTHß and RTHa) due to dominant negative variants in the genes encoding the thyroid hormone receptors alpha (THRA) and beta (THRB). The main question\[s\] it aims to answer are: * Define frequency and improve early diagnosis for RTH syndromes * Developing tools to accelerate diagnosis of RTH syndromes * Development and validation of monitoring tools Participants, recruited at neonatal screening or from cohorts of patients with unexplained specific neuro-cognitive or cardiovascular phenotypes will be submitted to biochemical and genetic investigations. In addition pluripotent stem cells will be generated from peripheral blood cells of RTHs patients and studied in vitro to understand the molecular mechanisms underlying neurological and cardiovascular consequences. In vitro and clinical data, will be correlated to identify biomarkers for monitoring treatment.