NOVEL INSIGHTS ON ALLAN-HERNDON-DUDLEY SYNDROME: TRANSCRIPTIONAL PROFILING AND FUNCTIONAL CHARACTERIZATION OF THREE GENETIC VARIANTS IN SLC16A2 GENE

Allan-Herndon-Dudley Syndrome (AHDS) is a rare genetic X-linked pediatric disorder, affecting essentially males, with intellectual and motor development impairment. It is caused by mutations in the SLC16A2 gene, which encodes for MCT8, a transporter responsible for thyroid hormone (TH) transport across cell membranes. THs are crucial for the development of several organs, mainly the brain and are involved in many physiological processes. Variants in SLC16A2 impact on the functionality and localization of MCT8 in various ways. The resulting clinical condition is characterized by brain hypothyroidism and thyrotoxicosis in peripheral tissues, leading to a range of symptoms, including cognitive delays, hypotonia, spasticity, and dystonia. In this study, we provide a deep investigation about the impact of three different pathological variants in SLC16A2 gene, identified in AHDS affected pediatric patients, on the pathogenetically mechanisms of AHDS. Particularly, from skin biopsies, we isolated primary fibroblasts from 3 AHDS patients and 2 healthy controls matched by sex and age to study the pathological readouts of the disease and identify novel related molecular pathways. With this purpose, we applied different techniques, including MTT and Live&Dead assays to characterize the obtained fibroblast cell lines. Moreover, we performed RT-qPCR, Western Blot, Immunofluorescence experiments, to investigate the functioning and the localization of MCT8 transporter in these cells. RNA-sequencing analysis provided us an overview about differentially expressed genes correlated to distinctive mechanisms of the disease, such as neuronal and glial specification deregulation; a reduced protein synthesis as a result of ribosome structural components’ impairment, a reduced mitochondrial activity and lipid droplets’ accumulation as a result of a disrupted thyroid hormone signaling. Overall, our study confirms the use of patients’ derived fibroblasts as a reliable model to study in vitro rare conditions, as well as showed us the importance of personalized medicine when patients carry different mutation related to the disease. Nevertheless, major limitations of the study are also exposed to represent the first starting point for overcoming them and finding a definitive cure for this debilitating condition.