Calcium ions (Ca2+) play a vital role in many biological processes. Transmembrane and coiled-coil domain 1 (TMCO1) has been characterized as an endoplasmic reticulum (ER) transmembrane protein in recent years. It keeps the cytoplasm and ER's Ca2+ homeostasis stable by acting as a novel calcium channel. Studies from different laboratories have revealed that the mutation or deficiency of TMCO1 is closely correlated with several diseases, including cerebro-facio-thoracic dysplasia (CFTD), glaucoma, premature ovarian failure (POF), osteoporosis, and cancer. Here, we review the characteristics of TMCO1 and its involvement in related diseases, which may provide useful information for developing therapeutic strategies for these diseases, as well as promote further research on this protein.

Craniofacial dysmorphism, skeletal anomalies, and impaired intellectual development syndrome-1 (CFSMR1; OMIM#213980) is a rare autosomal recessive disorder characterized by the clinical triad of developmental delay and/or intellectual disability, a typical facial gestalt with brachycephaly, highly-arched bushy eyebrows, synophrys, hypertelorism, wide nasal bridge, and short nose, as well as multiple vertebrae and rib malformations, such as bifid and fused ribs and abnormal vertebral segmentation and fusion. Biallelic loss-of-function variants in TMCO1 cause CFSMR1. We report on two unrelated Egyptian patients with a phenotype suggestive of CFSMR. Single whole-exome sequencing in patient 1 and Sanger sequencing of TMCO1 in patient 2 revealed the same homozygous TMCO1 nonsense variant c.187C > T/p.(Arg63*) in both affected individuals; patients' healthy parents were heterozygous carriers of the variant. Congenital hearing loss in patients 1 and 2 is an occasional finding in individuals affected by CFSMR. Camptodactyly and syndactyly, which were noted in patient 2, have not or rarely been reported in CFSMR. Review of the literature revealed a total of 30 individuals with the clinically recognizable and unique phenotype of CFSMR1, including the patients reported here, who all carried biallelic TMCO1 variants. Six different TMCO1 variants have been reported in the 30 patients from 14 families, comprising three nonsense, two 2-bp deletions, and a splice donor site variant. All disease-associated TMCO1 variants likely represent null alleles resulting in absence of the encoded protein. TMCO1 has been proposed to act as a Ca2+ channel, while other data revealed TMCO1 as a mitochondrial protein and a component of the translocon at the endoplasmic reticulum, a cellular machinery important for the biogenesis of multi-pass membrane proteins. RAB5IF/C20orf24 has recently been identified as causative gene for craniofacial dysmorphism, skeletal anomalies, and impaired intellectual development syndrome-2 (CFSMR2; OMIM#616994). Heterodimerization of RAB5IF/C20orf24 and TMCO1 and their interdependence may suggest a pathophysiological role of ER-mitochondria interaction underlying CFSMR.

Mitochondria are epicentres of eukaryotic metabolism and bioenergetics. Pioneering efforts in recent decades have established the core protein componentry of these organelles1 and have linked their dysfunction to more than 150 distinct disorders2,3. Still, hundreds of mitochondrial proteins lack clear functions4, and the underlying genetic basis for approximately 40% of mitochondrial disorders remains unresolved5. Here, to establish a more complete functional compendium of human mitochondrial proteins, we profiled more than 200 CRISPR-mediated HAP1 cell knockout lines using mass spectrometry-based multiomics analyses. This effort generated approximately 8.3 million distinct biomolecule measurements, providing a deep survey of the cellular responses to mitochondrial perturbations and laying a foundation for mechanistic investigations into protein function. Guided by these data, we discovered that PIGY upstream open reading frame (PYURF) is an S-adenosylmethionine-dependent methyltransferase chaperone that supports both complex I assembly and coenzyme Q biosynthesis and is disrupted in a previously unresolved multisystemic mitochondrial disorder. We further linked the putative zinc transporter SLC30A9 to mitochondrial ribosomes and OxPhos integrity and established RAB5IF as the second gene harbouring pathogenic variants that cause cerebrofaciothoracic dysplasia. Our data, which can be explored through the interactive online MITOMICS.app resource, suggest biological roles for many other orphan mitochondrial proteins that still lack robust functional characterization and define a rich cell signature of mitochondrial dysfunction that can support the genetic diagnosis of mitochondrial diseases.

Cerebrofaciothoracic dysplasia (CFTD) is a developmental disorder characterized by distinctive craniofacial dysmorphism, global developmental delay, and skeletal anomalies. CTFD is the result of biallelic autosomal recessive loss of function mutations in the transmembrane and coiled-coil domains one protein (TMCO1) gene. Based on a population of 27 molecularly confirmed cases, classic brain morphologies associated with CFTD have been described in the literature. Previous studies have demonstrated only mild ventriculomegaly, corpus callosum abnormalities, frontotemporal atrophy, and three cases of associated epilepsy. We present previously undescribed brain MRI findings in two children presenting with seizures due to TMCO1 mutation. MR Imaging demonstrated hippocampal malrotation, olfactory bulb agenesis and olfactory sulcus hypoplasia in both children, pontine hypoplasia, and cochlear nerve agenesis in one child. We demonstrate that TMCO1 may play a more extensive and previously undescribed role in neurodevelopment thereby expanding the phenotype associated with CFTD.