TANGO2 deficiency disease is predominantly caused by a lipid imbalance.

TANGO2 deficiency disease (TDD) is a rare genetic disorder estimated to affect ∼8000 individuals worldwide. It causes neurodegeneration often accompanied by potentially lethal metabolic crises that are triggered by diet or illness. Recent work has demonstrated distinct lipid imbalances in multiple model systems either depleted for or devoid of the TANGO2 protein, including human cells, fruit flies and zebrafish. Importantly, vitamin B5 supplementation has been shown to rescue TANGO2 deficiency-associated defects in flies and human cells. The notion that vitamin B5 is needed for synthesis of the lipid precursor coenzyme A (CoA) corroborates the hypothesis that key aspects of TDD pathology may be caused by lipid imbalance. A natural history study of 73 individuals with TDD reported that either multivitamin or vitamin B complex supplementation prevented the metabolic crises, suggesting this as a potentially life-saving treatment. Although recently published work supports this notion, much remains unknown about TANGO2 function, the pathological mechanism of TDD and the possible downsides of sustained vitamin supplementation in children and young adults. In this Perspective, we discuss these recent findings and highlight areas for immediate scientific attention.

Lipidomic analysis of human TANGO2-deficient cells suggests a lipid imbalance as a cause of TANGO2 deficiency disease.

TANGO2 deficiency disease (TDD) is a multisystem disease caused by variants in the TANGO2 gene. Symptoms include neurodevelopmental delays, seizures and potentially lethal metabolic crises and cardiac arrhythmias. While the function of TANGO2 remains elusive, vitamin B5/pantothenic acid supplementation has been shown to alleviate symptoms in a fruit fly model and has also been used with success to treat individuals suffering from TDD. Since vitamin B5 is the precursor to the lipid activator coenzyme A (CoA), we hypothesized that TANGO2-deficient cells would display changes in the lipid profile compared to control and that these changes would be rescued by vitamin B5 supplementation. In addition, the specific changes seen might point to a pathway in which TANGO2 functions. Indeed, we found profound changes in the lipid profile of human TANGO2-deficient cells as well as an increased pool of free fatty acids in both human cells devoid of TANGO2 and Drosophila harboring a previously described TANGO2 loss of function allele. All these changes were reversed upon vitamin B5 supplementation. Pathway analysis showed significant increases in triglyceride as well as in lysophospholipid levels as the top enriched pathways in the absence of TANGO2. Consistent with a defect in triglyceride metabolism, we found changes in lipid droplet numbers and sizes in the absence of TANGO2 compared to control. Our data will allow for comparison between other model systems of TDD and the homing in on critical lipid imbalances that lead to the disease state.

Haem's relevance genuine? Re-visiting the roles of TANGO2 homologues including HRG-9 and HRG-10 in C. elegans.

Mutations in the TANGO2 gene cause severe illness in humans, including life-threatening metabolic crises; however, the function of TANGO2 protein remains unknown. In a recent publication in Nature, Sun et al. proposed that TANGO2 helps transport haem within and between cells, from areas with high haem concentrations to those with lower concentrations. Caenorhabditis elegans has two versions of TANGO2 that Sun et al. called HRG-9 and HRG-10. They demonstrated that worms deficient in these proteins show increased survival upon exposure to a toxic haem analog, which Sun et al. interpreted as evidence of decreased haem uptake from intestinal cells into the rest of the organism. We repeated several experiments using the same C. elegans strain as Sun et al. and believe that their findings are better explained by reduced feeding behavior in these worms. We demonstrate that hrg-9 in particular is highly responsive to oxidative stress, independent of haem status. Our group also performed several experiments in yeast and zebrafish models of TANGO2 deficiency and was unable to replicate key findings from these models reported in Sun et al.'s original study. Overall, we believe there is insufficient evidence to support haem transport as the primary function for TANGO2.

Dynamic regulation of inter-organelle communication by ubiquitylation controls skeletal muscle development and disease onset.

Ubiquitin-proteasome system (UPS) dysfunction is associated with the pathology of a wide range of human diseases, including myopathies and muscular atrophy. However, the mechanistic understanding of specific components of the regulation of protein turnover during development and disease progression in skeletal muscle is unclear. Mutations in KLHL40, an E3 ubiquitin ligase cullin3 (CUL3) substrate-specific adapter protein, result in severe congenital nemaline myopathy, but the events that initiate the pathology and the mechanism through which it becomes pervasive remain poorly understood. To characterize the KLHL40-regulated ubiquitin-modified proteome during skeletal muscle development and disease onset, we used global, quantitative mass spectrometry-based ubiquitylome and global proteome analyses of klhl40a mutant zebrafish during disease progression. Global proteomics during skeletal muscle development revealed extensive remodeling of functional modules linked with sarcomere formation, energy, biosynthetic metabolic processes, and vesicle trafficking. Combined analysis of klh40 mutant muscle proteome and ubiquitylome identified thin filament proteins, metabolic enzymes, and ER-Golgi vesicle trafficking pathway proteins regulated by ubiquitylation during muscle development. Our studies identified a role for KLHL40 as a regulator of ER-Golgi anterograde trafficking through ubiquitin-mediated protein degradation of secretion-associated Ras-related GTPase1a (Sar1a). In KLHL40-deficient muscle, defects in ER exit site vesicle formation and downstream transport of extracellular cargo proteins result in structural and functional abnormalities. Our work reveals that the muscle proteome is dynamically fine-tuned by ubiquitylation to regulate skeletal muscle development and uncovers new disease mechanisms for therapeutic development in patients.

Natural history of TANGO2 deficiency disorder: Baseline assessment of 73 patients.

PURPOSE: TANGO2 deficiency disorder (TDD), an autosomal recessive disease first reported in 2016, is characterized by neurodevelopmental delay, seizures, intermittent ataxia, hypothyroidism, and life-threatening metabolic and cardiac crises. The purpose of this study was to define the natural history of TDD. METHODS: Data were collected from an ongoing natural history study of patients with TDD enrolled between February 2019 and May 2022. Data were obtained through phone or video based parent interviews and medical record review. RESULTS: Data were collected from 73 patients (59% male) from 57 unrelated families living in 16 different countries. The median age of participants at the time of data collection was 9.0 years (interquartile range = 5.3-15.9 years, range = fetal to 31.8 years). A total of 24 different TANGO2 alleles were observed. Patients showed normal development in early infancy, with progressive delay in developmental milestones thereafter. Symptoms included ataxia, dystonia, and speech difficulties, typically starting between the ages of 1 to 3 years. A total of 46/71 (65%) patients suffered metabolic crises, and of those, 30 (65%) developed cardiac crises. Metabolic crises were significantly decreased after the initiation of B-complex or multivitamin supplementation. CONCLUSION: We provide the most comprehensive review of natural history of TDD and important observational data suggesting that B-complex or multivitamins may prevent metabolic crises.

Vitamin B5, a coenzyme A precursor, rescues TANGO2 deficiency disease-associated defects in Drosophila and human cells.

Mutations in the Transport and Golgi Organization 2 (TANGO2) gene are associated with intellectual deficit, neurodevelopmental delay and regression. Individuals can also present with an acute metabolic crisis that includes rhabdomyolysis, cardiomyopathy, and cardiac arrhythmias, the latter of which are potentially lethal. While preventing metabolic crises has the potential to reduce mortality, no treatments currently exist for this condition. The function of TANGO2 remains unknown but is suspected to be involved in some aspect of lipid metabolism. Here, we describe a model of TANGO2-related disease in the fruit fly Drosophila melanogaster that recapitulates crucial disease traits. Pairing a new fly model with human cells, we examined the effects of vitamin B5, a coenzyme A (CoA) precursor, on alleviating the cellular and organismal defects associated with TANGO2 deficiency. We demonstrate that vitamin B5 specifically improves multiple defects associated with TANGO2 loss-of-function in Drosophila and rescues membrane trafficking defects in human cells. We also observed a partial rescue of one of the fly defects by vitamin B3, though to a lesser extent than vitamin B5. Our data suggest that a B complex supplement containing vitamin B5/pantothenate may have therapeutic benefits in individuals with TANGO2-deficiency disease. Possible mechanisms for the rescue are discussed that may include restoration of lipid homeostasis.

Biallelic variants in TRAPPC10 cause a microcephalic TRAPPopathy disorder in humans and mice.

The highly evolutionarily conserved transport protein particle (TRAPP) complexes (TRAPP II and III) perform fundamental roles in subcellular trafficking pathways. Here we identified biallelic variants in TRAPPC10, a component of the TRAPP II complex, in individuals with a severe microcephalic neurodevelopmental disorder. Molecular studies revealed a weakened interaction between mutant TRAPPC10 and its putative adaptor protein TRAPPC2L. Studies of patient lymphoblastoid cells revealed an absence of TRAPPC10 alongside a concomitant absence of TRAPPC9, another key TRAPP II complex component associated with a clinically overlapping neurodevelopmental disorder. The TRAPPC9/10 reduction phenotype was recapitulated in TRAPPC10-/- knockout cells, which also displayed a membrane trafficking defect. Notably, both the reduction in TRAPPC9 levels and the trafficking defect in these cells could be rescued by wild type but not mutant TRAPPC10 gene constructs. Moreover, studies of Trappc10-/- knockout mice revealed neuroanatomical brain defects and microcephaly, paralleling findings seen in the human condition as well as in a Trappc9-/- mouse model. Together these studies confirm autosomal recessive TRAPPC10 variants as a cause of human disease and define TRAPP-mediated pathomolecular outcomes of importance to TRAPPC9 and TRAPPC10 mediated neurodevelopmental disorders in humans and mice.

TRAPPC11-related muscular dystrophy with hypoglycosylation of alpha-dystroglycan in skeletal muscle and brain.

AIMS: TRAPPC11, a subunit of the transport protein particle (TRAPP) complex, is important for complex integrity and anterograde membrane transport from the endoplasmic reticulum (ER) to the ER-Golgi intermediate compartment. Several individuals with TRAPPC11 mutations have been reported with muscle weakness and other features including brain, liver, skeletal and eye involvement. A detailed analysis of brain and muscle pathology will further our understanding of the presentation and aetiology of TRAPPC11 disease. METHODS: We describe five cases of early-onset TRAPPC11-related muscular dystrophy with a systematic review of muscle pathology in all five individuals, post-mortem brain pathology findings in one and membrane trafficking assays in another. RESULTS: All affected individuals presented in infancy with muscle weakness, motor delay and elevated serum creatine kinase (CK). Additional features included cataracts, liver disease, intellectual disability, cardiomyopathy, movement disorder and structural brain abnormalities. Muscle pathology in all five revealed dystrophic changes, universal hypoglycosylation of alpha-dystroglycan and variably reduced dystrophin-associated complex proteins. Membrane trafficking assays showed defective Golgi trafficking in one individual. Neuropathological examination of one individual revealed cerebellar atrophy, granule cell hypoplasia, Purkinje cell (PC) loss, degeneration and dendrite dystrophy, reduced alpha-dystroglycan (IIH6) expression in PC and dentate neurones and absence of neuronal migration defects. CONCLUSIONS: This report suggests that recessive mutations in TRAPPC11 are linked to muscular dystrophies with hypoglycosylation of alpha-dystroglycan. The structural cerebellar involvement that we document for the first time resembles the neuropathology reported in N-linked congenital disorders of glycosylation (CDG) such as PMM2-CDG, suggesting defects in multiple glycosylation pathways in this condition.

The phenotype associated with variants in TANGO2 may be explained by a dual role of the protein in ER-to-Golgi transport and at the mitochondria.

TANGO2 variants result in a complex disease phenotype consisting of recurrent crisis-induced rhabdomyolysis, encephalopathy, seizures, lactic acidosis, hypoglycemia, and cardiac arrhythmias. Although first described in a fruit fly model as a protein necessary for some aspect of Golgi function and organization, its role in the cell at a fundamental level has not been addressed. Such studies are necessary to better counsel families regarding treatment options and nutrition management to mitigate the metabolic aspects of the disease. The few studies performed to address the pathway(s) in which TANGO2 functions have led to enigmatic results, with some suggesting defects in membrane traffic while others suggest unknown mitochondrial defects. Here, we have performed a robust membrane trafficking assay on fibroblasts derived from three different individuals harboring TANGO2 variants and show that there is a significant delay in the movement of cargo between the endoplasmic reticulum and the Golgi. Importantly, this delay was attributed to a defect in TANGO2 function. We further show that a portion of TANGO2 protein localizes to the mitochondria through a necessary but not sufficient stretch of amino acids at the amino terminus of the protein. Fibroblasts from affected individuals also displayed changes in mitochondrial morphology. We conclude that TANGO2 functions in both membrane trafficking and in some as yet undetermined role in mitochondria physiology. The phenotype of affected individuals can be partially explained by this dual involvement of the protein.

A novel homozygous variant in TRAPPC2L results in a neurodevelopmental disorder and disrupts TRAPP complex function.

BACKGROUND: Next-generation sequencing has facilitated the diagnosis of neurodevelopmental disorders with variable and non-specific clinical findings. Recently, a homozygous missense p.(Asp37Tyr) variant in TRAPPC2L, a core subunit of TRAPP complexes which function as tethering factors during membrane trafficking, was reported in two unrelated individuals with neurodevelopmental delay, post-infectious encephalopathy-associated developmental arrest, tetraplegia and accompanying rhabdomyolysis. METHODS: We performed whole genome sequencing on members of an Ashkenazi Jewish pedigree to identify the underlying genetic aetiology of global developmental delay/intellectual disability in three affected siblings. To assess the effect of the identified TRAPPC2L variant, we performed biochemical and cell biological functional studies on the TRAPPC2L protein. RESULTS: A rare homozygous predicted deleterious missense variant, p.(Ala2Gly), in TRAPPC2L was identified in the affected siblings and it segregated with the neurodevelopmental phenotype within the family. Using a yeast two-hybrid assay and in vitro binding, we demonstrate that the p.(Ala2Gly) variant, but not the p.(Asp37Tyr) variant, disrupted the interaction between TRAPPC2L and another core TRAPP protein, TRAPPC6a. Size exclusion chromatography suggested that this variant affects the assembly of TRAPP complexes. Employing two different membrane trafficking assays using fibroblasts from one of the affected siblings, we found a delay in traffic into and out of the Golgi. Similar to the p.(Asp37Tyr) variant, the p.(Ala2Gly) variant resulted in an increase in the levels of active RAB11. CONCLUSION: Our data fill in a gap in the knowledge of TRAPP architecture with TRAPPC2L interacting with TRAPPC6a, positioning it as a putative adaptor for other TRAPP subunits. Collectively, our findings support the pathogenicity of the TRAPPC2L p.(Ala2Gly) variant.

Publisher Correction: Characterization of three TRAPPC11 variants suggests a critical role for the extreme carboxy terminus of the protein.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

TRAPPing a neurological disorder: from yeast to humans.

The modular complex TRAPP acts as an activator of a subgroup of Ypt/RAB GTPases. The substrate GTPases and TRAPP are conserved from yeast to human cells, required for secretion and macroautophagy/autophagy and implicated in human disease. All TRAPP complexes contain four core subunits essential for cell viability, and until recently there were no human diseases associated with any core TRAPP subunit. Recently, we reported a neurological disorder associated with a pathogenic variant of the core TRAPP subunit TRAPPC4. This variant results in lower levels of full-length TRAPPC4 protein and the TRAPP complex. A conditional mutation of the yeast homolog of TRAPPC4, Trs23, also results in a lower level of the protein and the TRAPP complex. Phenotypic analysis of the yeast mutant cells reveals a minor defect in secretion and a major defect in autophagy. Similarly, primary fibroblasts derived from human patients also exhibit minor and severe defects in secretion and autophagy, respectively. We propose that the autophagy defect caused by the pathogenic-TRAPPC4 variant results in the severe neurological disorder. Moreover, we hypothesize that low levels of the core TRAPP complex are more detrimental to autophagy than to secretion, and that the long-term autophagy defect is especially harmful to neuronal cells.Abbreviations: ER: endoplasmic reticulum; PM: plasma membrane; TRAPP: transport protein particle; Ypt: yeast protein transport.

Deficiencies in vesicular transport mediated by TRAPPC4 are associated with severe syndromic intellectual disability.

The conserved transport protein particle (TRAPP) complexes regulate key trafficking events and are required for autophagy. TRAPPC4, like its yeast Trs23 orthologue, is a core component of the TRAPP complexes and one of the essential subunits for guanine nucleotide exchange factor activity for Rab1 GTPase. Pathogenic variants in specific TRAPP subunits are associated with neurological disorders. We undertook exome sequencing in three unrelated families of Caucasian, Turkish and French-Canadian ethnicities with seven affected children that showed features of early-onset seizures, developmental delay, microcephaly, sensorineural deafness, spastic quadriparesis and progressive cortical and cerebellar atrophy in an effort to determine the genetic aetiology underlying neurodevelopmental disorders. All seven affected subjects shared the same identical rare, homozygous, potentially pathogenic variant in a non-canonical, well-conserved splice site within TRAPPC4 (hg19:chr11:g.118890966A>G; TRAPPC4: NM_016146.5; c.454+3A>G). Single nucleotide polymorphism array analysis revealed there was no haplotype shared between the tested Turkish and Caucasian families suggestive of a variant hotspot region rather than a founder effect. In silico analysis predicted the variant to cause aberrant splicing. Consistent with this, experimental evidence showed both a reduction in full-length transcript levels and an increase in levels of a shorter transcript missing exon 3, suggestive of an incompletely penetrant splice defect. TRAPPC4 protein levels were significantly reduced whilst levels of other TRAPP complex subunits remained unaffected. Native polyacrylamide gel electrophoresis and size exclusion chromatography demonstrated a defect in TRAPP complex assembly and/or stability. Intracellular trafficking through the Golgi using the marker protein VSVG-GFP-ts045 demonstrated significantly delayed entry into and exit from the Golgi in fibroblasts derived from one of the affected subjects. Lentiviral expression of wild-type TRAPPC4 in these fibroblasts restored trafficking, suggesting that the trafficking defect was due to reduced TRAPPC4 levels. Consistent with the recent association of the TRAPP complex with autophagy, we found that the fibroblasts had a basal autophagy defect and a delay in autophagic flux, possibly due to unsealed autophagosomes. These results were validated using a yeast trs23 temperature sensitive variant that exhibits constitutive and stress-induced autophagic defects at permissive temperature and a secretory defect at restrictive temperature. In summary we provide strong evidence for pathogenicity of this variant in a member of the core TRAPP subunit, TRAPPC4 that associates with vesicular trafficking and autophagy defects. This is the first report of a TRAPPC4 variant, and our findings add to the growing number of TRAPP-associated neurological disorders.

Characterization of three TRAPPC11 variants suggests a critical role for the extreme carboxy terminus of the protein.

TRAPPC11 was identified as a component of the TRAPP III complex that functions in membrane trafficking and autophagy. Variants in TRAPPC11 have been reported to be associated with a broad spectrum of phenotypes but all affected individuals display muscular pathology. Identifying additional variants will further our understanding of the clinical spectrum of phenotypes and will reveal regions of the protein critical for its functions. Here we report three individuals from unrelated families that have bi-allellic TRAPPC11 variants. Subject 1 harbors a compound heterozygous variant (c.1287 + 5G > A and c.3379_3380insT). The former variant results in a partial deletion of the foie gras domain (p.Ala372_Ser429del), while the latter variant results in a frame-shift and extension at the carboxy terminus (p.Asp1127Valfs*47). Subjects 2 and 3 both harbour a homozygous missense variant (c.2938G > A; p.Gly980Arg). Fibroblasts from all three subjects displayed membrane trafficking defects manifested as delayed endoplasmic reticulum (ER)-to-Golgi transport and/or a delay in protein exit from the Golgi. All three individuals also show a defect in glycosylation of an ER-resident glycoprotein. However, only the compound heterozygous subject displayed an autophagic flux defect. Collectively, our characterization of these individuals with bi-allelic TRAPPC11 variants highlights the functional importance of the carboxy-terminal portion of the protein.

TRAPPC11 functions in autophagy by recruiting ATG2B-WIPI4/WDR45 to preautophagosomal membranes.

TRAPPC11 has been implicated in membrane traffic and lipid-linked oligosaccharide synthesis, and mutations in TRAPPC11 result in neuromuscular and developmental phenotypes. Here, we show that TRAPPC11 has a role upstream of autophagosome formation during macroautophagy. Upon TRAPPC11 depletion, LC3-positive membranes accumulate prior to, and fail to be cleared during, starvation. A proximity biotinylation assay identified ATG2B and its binding partner WIPI4/WDR45 as TRAPPC11 interactors. TRAPPC11 depletion phenocopies that of ATG2 and WIPI4 and recruitment of both proteins to membranes is defective upon reduction of TRAPPC11. We find that a portion of TRAPPC11 and other TRAPP III proteins localize to isolation membranes. Fibroblasts from a patient with TRAPPC11 mutations failed to recruit ATG2B-WIPI4, suggesting that this interaction is physiologically relevant. Since ATG2B-WIPI4 is required for isolation membrane expansion, our study suggests that TRAPPC11 plays a role in this process. We propose a model whereby the TRAPP III complex participates in the formation and expansion of the isolation membrane at several steps.

TRAPPopathies: An emerging set of disorders linked to variations in the genes encoding transport protein particle (TRAPP)-associated proteins.

The movement of proteins between cellular compartments requires the orchestrated actions of many factors including Rab family GTPases, Soluble NSF Attachment protein REceptors (SNAREs) and so-called tethering factors. One such tethering factor is called TRAnsport Protein Particle (TRAPP), and in humans, TRAPP proteins are distributed into two related complexes called TRAPP II and III. Although thought to act as a single unit within the complex, in the past few years it has become evident that some TRAPP proteins function independently of the complex. Consistent with this, variations in the genes encoding these proteins result in a spectrum of human diseases with diverse, but partially overlapping, phenotypes. This contrasts with other tethering factors such as COG, where variations in the genes that encode its subunits all result in an identical phenotype. In this review, we present an up-to-date summary of all the known disease-related variations of genes encoding TRAPP-associated proteins and the disorders linked to these variations which we now call TRAPPopathies.

Bi-allelic mutations in TRAPPC2L result in a neurodevelopmental disorder and have an impact on RAB11 in fibroblasts.

BACKGROUND: The combination of febrile illness-induced encephalopathy and rhabdomyolysis has thus far only been described in disorders that affect cellular energy status. In the absence of specific metabolic abnormalities, diagnosis can be challenging. OBJECTIVE: The objective of this study was to identify and characterise pathogenic variants in two individuals from unrelated families, both of whom presented clinically with a similar phenotype that included neurodevelopmental delay, febrile illness-induced encephalopathy and episodes of rhabdomyolysis, followed by developmental arrest, epilepsy and tetraplegia. METHODS: Whole exome sequencing was used to identify pathogenic variants in the two individuals. Biochemical and cell biological analyses were performed on fibroblasts from these individuals and a yeast two-hybrid analysis was used to assess protein-protein interactions. RESULTS: Probands shared a homozygous TRAPPC2L variant (c.109G>T) resulting in a p.Asp37Tyr missense variant. TRAPPC2L is a component of transport protein particle (TRAPP), a group of multisubunit complexes that function in membrane traffic and autophagy. Studies in patient fibroblasts as well as in a yeast system showed that the p.Asp37Tyr protein was present but not functional and resulted in specific membrane trafficking delays. The human missense mutation and the analogous mutation in the yeast homologue Tca17 ablated the interaction between TRAPPC2L and TRAPPC10/Trs130, a component of the TRAPP II complex. Since TRAPP II activates the GTPase RAB11, we examined the activation state of this protein and found increased levels of the active RAB, correlating with changes in its cellular morphology. CONCLUSIONS: Our study implicates a RAB11 pathway in the aetiology of the TRAPPC2L disorder and has implications for other TRAPP-related disorders with similar phenotypes.

TRAPPC11 and GOSR2 mutations associate with hypoglycosylation of α-dystroglycan and muscular dystrophy.

BACKGROUND: Transport protein particle (TRAPP) is a supramolecular protein complex that functions in localizing proteins to the Golgi compartment. The TRAPPC11 subunit has been implicated in muscle disease by virtue of homozygous and compound heterozygous deleterious mutations being identified in individuals with limb girdle muscular dystrophy and congenital muscular dystrophy. It remains unclear how this protein leads to muscle disease. Furthermore, a role for this protein, or any other membrane trafficking protein, in the etiology of the dystroglycanopathy group of muscular dystrophies has yet to be found. Here, using a multidisciplinary approach including genetics, immunofluorescence, western blotting, and live cell analysis, we implicate both TRAPPC11 and another membrane trafficking protein, GOSR2, in α-dystroglycan hypoglycosylation. CASE PRESENTATION: Subject 1 presented with severe epileptic episodes and subsequent developmental deterioration. Upon clinical evaluation she was found to have brain, eye, and liver abnormalities. Her serum aminotransferases and creatine kinase were abnormally high. Subjects 2 and 3 are siblings from a family unrelated to subject 1. Both siblings displayed hypotonia, muscle weakness, low muscle bulk, and elevated creatine kinase levels. Subject 3 also developed a seizure disorder. Muscle biopsies from subjects 1 and 3 were severely dystrophic with abnormal immunofluorescence and western blotting indicative of α-dystroglycan hypoglycosylation. Compound heterozygous mutations in TRAPPC11 were identified in subject 1: c.851A>C and c.965+5G>T. Cellular biological analyses on fibroblasts confirmed abnormal membrane trafficking. Subject 3 was found to have compound heterozygous mutations in GOSR2: c.430G>T and c.2T>G. Cellular biological analyses on fibroblasts from subject 3 using two different model cargo proteins did not reveal defects in protein transport. No mutations were found in any of the genes currently known to cause dystroglycanopathy in either individual. CONCLUSION: Recessive mutations in TRAPPC11 and GOSR2 are associated with congenital muscular dystrophy and hypoglycosylation of α-dystroglycan. This is the first report linking membrane trafficking proteins to dystroglycanopathy and suggests that these genes should be considered in the diagnostic evaluation of patients with congenital muscular dystrophy and dystroglycanopathy.

Mutations in TRAPPC12 Manifest in Progressive Childhood Encephalopathy and Golgi Dysfunction.

Progressive childhood encephalopathy is an etiologically heterogeneous condition characterized by progressive central nervous system dysfunction in association with a broad range of morbidity and mortality. The causes of encephalopathy can be either non-genetic or genetic. Identifying the genetic causes and dissecting the underlying mechanisms are critical to understanding brain development and improving treatments. Here, we report that variants in TRAPPC12 result in progressive childhood encephalopathy. Three individuals from two unrelated families have either a homozygous deleterious variant (c.145delG [p.Glu49Argfs∗14]) or compound-heterozygous variants (c.360dupC [p.Glu121Argfs∗7] and c.1880C>T [p. Ala627Val]). The clinical phenotypes of the three individuals are strikingly similar: severe disability, microcephaly, hearing loss, spasticity, and characteristic brain imaging findings. Fibroblasts derived from all three individuals showed a fragmented Golgi that could be rescued by expression of wild-type TRAPPC12. Protein transport from the endoplasmic reticulum to and through the Golgi was delayed. TRAPPC12 is a member of the TRAPP protein complex, which functions in membrane trafficking. Variants in several other genes encoding members of the TRAPP complex have been associated with overlapping clinical presentations, indicating shared and distinct functions for each complex member. Detailed understanding of the TRAPP-opathies will illuminate the role of membrane protein transport in human disease.

A novel TRAPPC11 mutation in two Turkish families associated with cerebral atrophy, global retardation, scoliosis, achalasia and alacrima.

BACKGROUND: Triple A syndrome (MIM #231550) is associated with mutations in the AAAS gene. However, about 30% of patients with triple A syndrome symptoms but an unresolved diagnosis do not harbour mutations in AAAS. OBJECTIVE: Search for novel genetic defects in families with a triple A-like phenotype in whom AAAS mutations are not detected. METHODS: Genome-wide linkage analysis, whole-exome sequencing and functional analyses were used to discover and verify a novel genetic defect in two families with achalasia, alacrima, myopathy and further symptoms. Effect and pathogenicity of the mutation were verified by cell biological studies. RESULTS: We identified a homozygous splice mutation in TRAPPC11 (c.1893+3A>G, [NM_021942.5], g.4:184,607,904A>G [hg19]) in four patients from two unrelated families leading to incomplete exon skipping and reduction in full-length mRNA levels. TRAPPC11 encodes for trafficking protein particle complex subunit 11 (TRAPPC11), a protein of the transport protein particle (TRAPP) complex. Western blot analysis revealed a dramatic decrease in full-length TRAPPC11 protein levels and hypoglycosylation of LAMP1. Trafficking experiments in patient fibroblasts revealed a delayed arrival of marker proteins in the Golgi and a delay in their release from the Golgi to the plasma membrane. Mutations in TRAPPC11 have previously been described to cause limb-girdle muscular dystrophy type 2S (MIM #615356). Indeed, muscle histology of our patients also revealed mild dystrophic changes. Immunohistochemically, ß-sarcoglycan was absent from focal patches. CONCLUSIONS: The identified novel TRAPPC11 mutation represents an expansion of the myopathy phenotype described before and is characterised particularly by achalasia, alacrima, neurological and muscular phenotypes.