Wang QC, etal., Cell. 2016 Jun 2;165(6):1454-66. doi: 10.1016/j.cell.2016.04.051. Epub 2016 May 19.
Maintaining homeostasis of Ca(2+) stores in the endoplasmic reticulum (ER) is crucial for proper Ca(2+) signaling and key cellular functions. The Ca(2+)-release-activated Ca(2+) (CRAC) channel is responsible for Ca(2+) influx and refilling after store depletion, but how cells cope with excess Ca(2+)
when ER stores are overloaded is unclear. We show that TMCO1 is an ER transmembrane protein that actively prevents Ca(2+) stores from overfilling, acting as what we term a "Ca(2+) load-activated Ca(2+) channel" or "CLAC" channel. TMCO1 undergoes reversible homotetramerization in response to ER Ca(2+) overloading and disassembly upon Ca(2+) depletion and forms a Ca(2+)-selective ion channel on giant liposomes. TMCO1 knockout mice reproduce the main clinical features of human cerebrofaciothoracic (CFT) dysplasia spectrum, a developmental disorder linked to TMCO1 dysfunction, and exhibit severe mishandling of ER Ca(2+) in cells. Our findings indicate that TMCO1 provides a protective mechanism to prevent overfilling of ER stores with Ca(2+) ions.
Alanay Y, etal., Am J Med Genet A. 2014 Feb;164A(2):291-304. doi: 10.1002/ajmg.a.36248. Epub 2013 Nov 5.
Cerebrofaciothoracic dysplasia (CFT) (OMIM #213980) is a multiple congenital anomaly and intellectual disability syndrome involving the cranium, face, and thorax. The characteristic features are cranial involvement with macrocrania at birth, brachycephaly, various CT/MRI findings including hypoplasi
a of corpus callosum, enlargement of septum pellicidum, and diffuse hypodensity of the grey matter, flat face, hypertelorism, cleft lip and cleft palate, low-set, posteriorly rotated ears, short neck, and multiple costal and vertebral anomalies. The underlying genetic defect remains unknown. Using combination of homozygosity mapping and whole-exome sequencing, we identified a homozygous nonsense founder mutation, p.Arg87Ter (c.259 C>T), in the human transmembrane and coiled-coil domains protein 1 (TMCO1) in four out of five families of Turkish origin. The entire critical region on chromosome 1q24 containing TMCO1 was excluded in the fifth family with characteristic findings of CFT providing evidence for genetic heterogeneity of CFT spectrum. Another founder TMCO1 mutation has recently been reported to cause a unique genetic condition, TMCO1-defect syndrome (OMIM #614132). TMCO1-defect syndrome shares many features with CFT. This study supports the fact that "TMCO1-defect syndrome," initially thought to represent a distinct disorder, indeed belongs to the genetically heterogeneous CFT dysplasia spectrum.
Whole-exome sequencing (WES) is a type of disruptive technology that has tremendous influence on human and clinical genetics research. An efficient and cost-effective method, WES is now widely used as a diagnostic tool for identifying the molecular basis of genetic syndromes that are often challengi
ng to diagnose. Here we report a patient with a clinical diagnosis of cerebro-facio-thoracic dysplasia (CFTD; MIM#213980) in whom we identified a homozygous splice-site mutation in the transmembrane and coiled-coil domains 1 (TMCO1) gene using WES. TMCO1 mutations cause craniofacial dysmorphism, skeletal anomalies characterized by multiple malformations of the vertebrae and ribs, and intellectual disability (MIM#614132). A retrospective review revealed that clinical manifestations of both syndromes are very similar and overlap remarkably. We propose that mutations of TMCO1 are not only responsible for craniofacial dysmorphism, skeletal anomalies and mental retardation syndrome but also for CFTD.
Xin B, etal., Proc Natl Acad Sci U S A. 2010 Jan 5;107(1):258-63. doi: 10.1073/pnas.0908457107. Epub 2009 Dec 14.
We identified an autosomal recessive condition in 11 individuals in the Old Order Amish of northeastern Ohio. The syndrome was characterized by distinctive craniofacial dysmorphism, skeletal anomalies, and mental retardation. The typical craniofacial dysmorphism included brachycephaly, highly arched
bushy eyebrows, synophrys, long eyelashes, low-set ears, microdontism of primary teeth, and generalized gingival hyperplasia, whereas Sprengel deformity of scapula, fusion of spine, rib abnormities, pectus excavatum, and pes planus represented skeletal anomalies. The genome-wide homozygosity mapping using six affected individuals localized the disease gene to a 3.3-Mb region on chromosome 1q23.3-q24.1. Candidate gene sequencing identified a homozygous frameshift mutation, c.139_140delAG, in the transmembrane and coiled-coil domains 1 (TMCO1) gene, as the pathogenic change in all affected members of the extended pedigree. This mutation is predicted to result in a severely truncated protein (p.Ser47Ter) of only one-fourth the original length. The TMCO1 gene product is a member of DUF841 superfamily of several eukaryotic proteins with unknown function. The gene has highly conserved amino acid sequence and is universally expressed in all human tissues examined. The high degree of conservation and the ubiquitous expression pattern in human adult and fetal tissues suggest a critical role for TMCO1. This report shows a TMCO1 sequence variant being associated with a genetic disorder in human. We propose "TMCO1 defect syndrome" as the name of this condition.
