From Disease Description and Gene Discovery to Functional Cell Pathway: A Decade-Long Journey for TMCO1

Abstract

A decade has passed since transmembrane coiled-coil domains 1 (TMCO1) defect syndrome was identified in 11 undiagnosed patients within the Old Order Amish of Northeastern Ohio-a disorder characterized by a distinctive craniofacial dysmorphism, skeletal anomalies and global developmental delay. Twenty seven patients, from diverse ethnic groups, have been reported with pathogenic TMCO1 variants now recognized to cause cerebrofaciothoracic dysplasia (CFTD). The implication of previously uncharacterized TMCO1 within disease has instigated a 10-year journey to understand the function of TMCO1 protein in Ca²⁺ homeostasis. TMCO1 is an ER Ca²⁺ leak channel which facilitates Ca²⁺ leak upon ER "overload" through the novel Ca²⁺ load activated Ca²⁺ mechanism. This mini-review brings together the clinical and scientific advances made since the discovery of TMCO1 deficiency in disease, including broadened phenotype, understanding of pathophysiology, and implications to patient management of TMCO1 defect syndrome.

Keywords: CFTD; CLAC channel; TMCO1; TMCO1 defect syndrome; calcium; cerebrofaciothoracic dysplasia.

FIGURE 1

Schematic of TMC01 function. TMCO1 exists as monomers and dimers during basal ER Ca²⁺ load. ER Ca²⁺ reaching overload results in oligomerization to form active TMCO1 tetrameric channels, facilitating Ca²⁺ release. Channels undergo rapid disassembly once basal Ca²⁺ levels are restored. Mutated TMCO1 is unable to assemble to form active channels resulting in persistent ER Ca²⁺ overload.