Identification of a localized nonsense-mediated decay pathway at the endoplasmic reticulum.

Nonsense-mediated decay (NMD) is a translation-dependent RNA quality control mechanism that occurs in the cytoplasm. However, it is unknown how NMD regulates the stability of RNAs translated at the endoplasmic reticulum (ER). Here, we identify a localized NMD pathway dedicated to ER-translated mRNAs. We previously identified NBAS, a component of the Syntaxin 18 complex involved in Golgi-to-ER trafficking, as a novel NMD factor. Furthermore, we show that NBAS fulfills an independent function in NMD. This ER-NMD pathway requires the interaction of NBAS with the core NMD factor UPF1, which is partially localized at the ER in the proximity of the translocon. NBAS and UPF1 coregulate the stability of ER-associated transcripts, in particular those associated with the cellular stress response. We propose a model where NBAS recruits UPF1 to the membrane of the ER and activates an ER-dedicated NMD pathway, thus providing an ER-protective function by ensuring quality control of ER-translated mRNAs.

Impact of genetic and non-genetic factors on phenotypic diversity in NBAS-associated disease.

Biallelic pathogenic variants in neuroblastoma-amplified sequence (NBAS) cause a pleiotropic multisystem disorder. Three clinical subgroups have been defined correlating with the localisation of pathogenic variants in the NBAS gene: variants affecting the C-terminal region of NBAS result in SOPH syndrome (short stature, optic atrophy, Pelger-Huët anomaly), variants affecting the Sec 39 domain are associated with infantile liver failure syndrome type 2 (ILFS2) and variants affecting the ß-propeller domain give rise to a combined phenotype. However, there is still unexplained phenotypic diversity across the three subgroups, challenging the current concept of genotype-phenotype correlations in NBAS-associated disease. Therefore, besides examining the genetic influence, we aim to elucidate the potential impact of pre-symptomatic diagnosis, emergency management and other modifying variables on the clinical phenotype. We investigated genotype-phenotype correlations in individuals sharing the same genotypes (n = 30 individuals), and in those sharing the same missense variants with a loss-of-function variant in trans (n = 38 individuals). Effects of a pre-symptomatic diagnosis and emergency management on the severity of acute liver failure (ALF) episodes also were analysed, comparing liver function tests (ALAT, ASAT, INR) and mortality. A strong genotype-phenotype correlation was demonstrated in individuals sharing the same genotype; this was especially true for the ILFS2 subgroup. Genotype-phenotype correlation in patients sharing only one missense variant was still high, though at a lower level. Pre-symptomatic diagnosis in combination with an emergency management protocol leads to a trend of reduced severity of ALF. High genetic impact on clinical phenotype in NBAS-associated disease facilitates monitoring and management of affected patients sharing the same genotype. Pre-symptomatic diagnosis and an emergency management protocol do not prevent ALF but may reduce its clinical severity.

Disorders of vesicular trafficking presenting with recurrent acute liver failure: NBAS, RINT1, and SCYL1 deficiency.

Among genetic disorders of vesicular trafficking, there are three causing recurrent acute liver failure (RALF): NBAS, RINT1, and SCYL1-associated disease. These three disorders are characterized by liver crises triggered by febrile infections and account for a relevant proportion of RALF causes. While the frequency and severity of liver crises in NBAS and RINT1-associated disease decrease with age, patients with SCYL1 variants present with a progressive, cholestatic course. In all three diseases, there is a multisystemic, partially overlapping phenotype with variable expression, including liver, skeletal, and nervous systems, all organ systems with high secretory activity. There are no specific biomarkers for these diseases, and whole exome sequencing should be performed in patients with RALF of unknown etiology. NBAS, SCYL1, and RINT1 are involved in antegrade and retrograde vesicular trafficking. Pathomechanisms remain unclarified, but there is evidence of a decrease in concentration and stability of the protein primarily affected by the respective gene defect and its interaction partners, potentially causing impairment of vesicular transport. The impairment of protein secretion by compromised antegrade transport provides a possible explanation for different organ manifestations such as bone alteration due to lack of collagens or diabetes mellitus when insulin secretion is affected. Dysfunction of retrograde transport impairs membrane recycling and autophagy. The impairment of vesicular trafficking results in increased endoplasmic reticulum stress, which, in hepatocytes, can progress to hepatocytolysis. While there is no curative therapy, an early and consequent implementation of an emergency protocol seems crucial for optimal therapeutic management.

Origins of SOPH syndrome: A study of 93 Yakut patients with review of C-terminal phenotype.

Since the first report of SOPH syndrome among the Yakut population in 2010, new clinical data of SOPH-like conditions continue to appear. We expand the phenotypic spectrum of SOPH syndrome and perform a comparative analysis of Yakut SOPH patients' clinical data with SOPH-like conditions reported in the world scientific literature to form a foundation for NBAS pathogenesis discussion. Clinical data from the genetic records of 93 patients with SOPH syndrome and global survey data on patients with pathogenic variants of the C-terminal in the NBAS gene were collected. A detailed phenotype description of patients is presented with a total number of 111 individuals. Underweight below the fifth centile and prone to delayed bone age in Yakut SOPH patients are retrospectively observed. We outline the short stature with optic atrophy as the leading phenotyping trait for C-terminal NBAS patients. The pathophysiology and patients management of SOPH-like conditions are discussed.

Modulation of NBAS-Related Functions in the Early Response to SARS-CoV-2 Infection.

Upon infection, severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) is predicted to interact with diverse cellular functions, such as the nonsense-mediated decay (NMD) pathway, as suggested by the identification of the core NMD factor upframeshift-1 (UPF1) in the SARS-CoV-2 interactome, and the retrograde transport from the Golgi to the endoplasmic reticulum (ER) through the endoplasmic reticulum-Golgi intermediate compartment (ERGIC), where coronavirus assembly occurs. Here, we investigated the expression and localization of the neuroblastoma-amplified sequence (NBAS) protein, a UPF1 partner for the NMD at the ER, participating also in retrograde transport, and of its functional partners, at early time points after SARS-CoV-2 infection of the human lung epithelial cell line Calu3. We found a significant decrease of DExH-Box Helicase 34 (DHX34), suppressor with morphogenetic effect on genitalia 5 (SMG5), and SMG7 expression at 6 h post-infection, followed by a significant increase of these genes and also UPF1 and UPF2 at 9 h post-infection. Conversely, NBAS and other genes coding for NMD factors were not modulated. Known NMD substrates related to cell stress (Growth Arrest Specific 5, GAS5; transducin beta-like 2, TBL2; and DNA damage-inducible transcript 3, DDIT3) were increased in infected cells, possibly as a result of alterations in the NMD pathway and of a direct effect of the infection. We also found that the expression of unconventional SNARE in the ER 1, USE1 (p31) and Zeste White 10 homolog, ZW10, partners of NBAS in the retrograde transport function, significantly increased over time in infected cells. Co-localization of NBAS and UPF1 proteins did not change within 24 h of infection nor did it differ in infected versus non-infected cells at 1 and 24 h after infection; similarly, the co-localization of NBAS and p31 proteins was not altered by infection in this short time frame. Finally, both NBAS and UPF1 were found to co-localize with SARS-CoV-2 S and N proteins. Overall, these data are preliminary evidence of an interaction between NBAS and NBAS-related functions and SARS-CoV-2 in infected cells, deserving further investigation.

What are the clues for an inherited metabolic disorder in Reye syndrome? A single Centre study of 58 children.

OBJECTIVES: Reye Syndrome is an acute encephalopathy with increased liver enzymes and blood ammonia, without jaundice. The prevalence of an underlying inherited metabolic disorder (IMD) is unclear, nor the clinical or biological factors directing toward this diagnosis. Our aims were to define these clues in a large series of patients. PATIENTS AND METHODS: We retrospectively studied all patients with Reye admitted in our institution from 1995. We defined 3 groups: Group 1 with a confirmed IMD, Group 2 considered as free of IMD, Group 3 unclassified. Statistical analysis compared patients in Groups 1 and 2, to find criteria for a diagnosis of IMD. RESULTS: Fifty-eight children were included; 41 (71%) had a confirmed IMD, 12 (20%) were free of IMD, and 5 remained unclassified. IMDs included Urea Cycle Disorders (51%), Fatty-Acid Oxidation Disorders (24%), ketogenesis defects (5%), other mitochondrial energy metabolism defects (10%), NBAS mutation (7%), Glycosylation Disorders (2%). In Group 2, the trigger was a viral infection, or a drug, deferasirox in three children. Univariate analysis showed that onset before 2 years-old, recurrent Reye and the association with rhabdomyolysis were significantly associated with IMD. Blood ammonia was a poor discriminating marker. All children were admitted into the intensive care unit, 23% needed continuous venovenous hemodialysis and one died from brain oedema. CONCLUSION: Metabolic tests should be performed early in all cases of Reye, regardless of triggers. As they can be inconclusive, we suggest to systematically go to Next-Generation Sequencing study. These children should be transferred early to a specialized unit.

Neurobehavioural challenges experienced by HIV exposed infants: a study in South Africa.

BACKGROUND: The newborn infant is a complexly organized, competent being, who plays an active role in shaping their environment through their increasing skills in autonomic regulation, motor control, regulation of state and social interaction. Infants born to HIV positive mothers, are exposed to HIV and antiretroviral therapy inutero, and may experience adverse effects from this. METHODS: A cross-sectional study of 132 mother-infant dyads from a large public health hospital in South Africa. Infants were assessed using the Neonatal Behavioural Assessment Scale on day two of life, and mothers mental health assessed using the Edinburugh Postnatal Depression Scale. Medical and demographic data on mothers and infants was collected, including maternal age, HIV status, length of time on antiretrovirals, relationship status, employment status, gravid status, mode of delivery, infant anthropometrics and infant gender. Data was input into IBM SPSS statistics 21, where frequencies and percentages for descriptive analysis, and Chi-square and student's two sample t-tests were run to compare data from HIV infected-exposed and HIV uninfected-unexposed mothers and infants. RESULTS: HIV exposed infants were smaller than HIV unexposed infants, even though low birth weight was an exclusion criteria. Statistically significant differences were found between HIV exposed and unexposed infants in neurobehavioiral items of social interaction (p = 0.00), motor system (p = 0.00) and state organization (p = 0.01), with HIV exposed infants performing less optimally in these domains. HIV exposed infants also presented with more abnormal reflexes. Infants born to depressed mothers showed superior motor skills, state organization and state regulation than infants born to mothers who did not score in the possibly depressed range. CONCLUSIONS: HIV exposed infants have inferior neurobehavioural functioning, which may affect their quality of life and ability to develop a reciprocal relationship with a primary caregiver. This may have an effect on development, behaviour and mental health in later childhood. HIV exposed infants shoud be monitored closely and their functioning in autonomic stability, motor control, resualtion of state and social interaction assessed regularly. Guidance for caregivers in incorporating strategies into the care of these infants is essential to buffer the possible long term negative effects on development.

Case report: A novel cause of acute liver failure in children: A combination of human herpesvirus-6 infection and homozygous mutation in NBAS gene.

Etiologies of acute liver failure in children can be multiple factors including virus infection, drug-induced damage, and different pathogens. Next-generation sequencing (NGS) is an emerging method for pan-pathogen screening. Here we reported a case of acute liver failure in a 15-month-old male, using NGS and gene sequencing to determine the cause of acute liver failure may be caused by pathogens, drug-induction and pathogenic variant gene.

NBAS Variants Are Associated with Quantitative and Qualitative NK and B Cell Deficiency.

PURPOSE: Biallelic pathogenic NBAS variants manifest as a multisystem disorder with heterogeneous clinical phenotypes such as recurrent acute liver failure, growth retardation, and susceptibility to infections. This study explores how NBAS-associated disease affects cells of the innate and adaptive immune system. METHODS: Clinical and laboratory parameters were combined with functional multi-parametric immunophenotyping methods in fifteen NBAS-deficient patients to discover possible alterations in their immune system. RESULTS: Our study revealed reduced absolute numbers of mature CD56dim natural killer (NK) cells. Notably, the residual NK cell population in NBAS-deficient patients exerted a lower potential for activation and degranulation in response to K562 target cells, suggesting an NK cell-intrinsic role for NBAS in the release of cytotoxic granules. NBAS-deficient NK cell activation and degranulation was normalized upon pre-activation by IL-2 in vitro, suggesting that functional impairment was reversible. In addition, we observed a reduced number of naïve B cells in the peripheral blood associated with hypogammaglobulinemia. CONCLUSION: In summary, we demonstrate that pathogenic biallelic variants in NBAS are associated with dysfunctional NK cells as well as impaired adaptive humoral immunity.

Characterization of a complex phenotype (fever-dependent recurrent acute liver failure and osteogenesis imperfecta) due to NBAS and P4HB variants.

We report the clinical, biochemical and genetic findings from a Spanish boy of Caucasian origin who presented with fever-dependent RALF (recurrent acute liver failure) and osteogenesis imperfecta (OI). Whole-exome sequencing (WES) uncovered two compound heterozygous variants in NBAS (c.[1265 T > C];[1549C > T]:p.[(Leu422Pro)];[(Arg517Cys)]), and a heterozygous variant in P4HB (c.[194A > G];[194=]:p.[(Lys65Arg)];[(Lys65=)]) that was transmitted from the clinically unaffected mother who was mosaic carrier of the variant. Variants in NBAS protein have been associated with ILFS2 (infantile liver failure syndrome-2), SOPH syndrome (short stature, optic nerve atrophy, and Pelger-Huët anomaly syndrome), and multisystem diseases. Several patients showed clinical manifestations affecting the skeletal system, such as osteoporosis, pathologic fractures and OI. Experiments in the patient's fibroblasts demonstrated that mutated NBAS protein is overexpressed and thermally unstable, and reduces the expression of MGP, a regulator of bone homeostasis. Variant in PDI (protein encoded by P4HB) has been associated with CLCRP1 (Cole-Carpenter syndrome-1), a type of severe OI. An increase of COL1A2 protein retention was observed in the patient's fibroblasts. In order to study if the variant in P4HB was involved in the alteration in collagen trafficking, overexpression experiments of PDI were carried out. These experiments showed that overexpression of mutated PDI protein produces an increase in COL1A2 retention. In conclusion, these results corroborate that the variants in NBAS are responsible for the liver phenotype, and demonstrate that the variant in P4HB is involved in the bone phenotype, probably in synergy with NBAS variants.

Study of Acute Liver Failure in Children Using Next Generation Sequencing Technology.

OBJECTIVE: To use next generation sequencing (NGS) technology to identify undiagnosed, monogenic diseases in a cohort of children who suffered from acute liver failure (ALF) without an identifiable etiology. STUDY DESIGN: We identified 148 under 10 years of age admitted to King's College Hospital, London, with ALF of indeterminate etiology between 2000 and 2018. A custom NGS panel of 64 candidate genes known to cause ALF and/or metabolic liver disease was constructed. Targeted sequencing was carried out on 41 children in whom DNA samples were available. Trio exome sequencing was performed on 4 children admitted during 2019. A comparison of the clinical characteristics of those identified with biallelic variants against those without biallelic variants was then made. RESULTS: Homozygous and compound heterozygous variants were identified in 8 out of 41 children (20%) and 4 out of 4 children (100%) in whom targeted and exome sequencing were carried out, respectively. The genes involved were NBAS (3 children); DLD (2 children); and CPT1A, FAH, LARS1, MPV17, NPC1, POLG, SUCLG1, and TWINK (1 each). The 12 children who were identified with biallelic variants were younger at presentation and more likely to die in comparison with those who did not: median age at presentation of 3 months and 30 months and survival rate 75% and 97%, respectively. CONCLUSIONS: NGS was successful in identifying several specific etiologies of ALF. Variants in NBAS and mitochondrial DNA maintenance genes were the most common findings. In the future, a rapid sequencing NGS workflow could help in reaching a timely diagnosis and facilitate clinical decision making in children with ALF.

Resolution of recurrent pediatric acute liver failure with liver transplantation in a patient with NBAS mutation.

BACKGROUND: Pediatric acute liver failure (PALF) remains an enigmatic process of rapid end-organ dysfunction associated with a variety of pathologic conditions though the predominant cause is indeterminate. A growing body of research has identified mutations in the NBAS gene to be associated with recurrent acute liver failure and multi-systemic disease including short stature, skeletal dysplasia, facial dysmorphism, immunologic abnormalities, and Pelger-Huët anomaly. METHODS AND RESULTS: Here, we describe a 4-year-old girl who presented with dehydration in the setting of acute gastroenteritis and fever but went on to develop PALF on day 2 of hospitalization. She clinically recovered with supportive measures, but after discharge, had at least 2 additional episodes of PALF. Ultimately, she underwent liver transplant and her recurrent episodes of PALF did not recur throughout a 6-year follow-up period. Whole-exome sequencing post-liver transplant initially revealed two variants of uncertain significance in the NBAS gene. Parental studies confirmed the c.1549C > T(p.R517C; now likely pathogenic) variant from her mother and a novel c.4646T > C(p.L1549P) variant from her father. In silico analyses predicted these variants to have a deleterious effect on protein function. Consistent with previously characterized NBAS mutation-associated disease (NMAD), our patient demonstrated the following features: progeroid facial features, hypoplasia of the 12th ribs, Pelger-Huët anomaly on peripheral blood smear, and abnormal B and NK cell function. CONCLUSION: Altogether, we describe a novel pathogenic variant in the NBAS gene of a patient with NMAD and report the resolution of recurrent PALF secondary to NMAD following liver transplantation.

NBAS deficiency due to biallelic c.2809C > G variant presenting with recurrent acute liver failure with severe hyperammonemia, acquired microcephaly and progressive brain atrophy.

Biallelic pathogenic variants in the neuroblastoma amplified sequence (NBAS) gene were firstly (2015) identified as a cause of fever-triggered recurrent acute liver failure (RALF). Since then, some patients with NBAS deficiency presenting with neurologic features, including a motor delay, intellectual disability, muscular hypotonia and a mild brain atrophy, have been reported. Here, we describe a case of pediatric patient diagnosed with NBAS deficiency due to a homozygous c.2809C > G, p.(Pro937Ala) variant presenting with RALF with severe hyperammonemia, acquired microcephaly and progressive brain atrophy. Not reported in the literature findings include severe hyperammonemia during ALF episode, and neurologic features in the form of acquired progressive microcephaly with brain atrophy. The latter raises the hypothesis about a primary neurologic phenotype in NBAS deficiency.

Defining clinical subgroups and genotype-phenotype correlations in NBAS-associated disease across 110 patients.

PURPOSE: Pathogenic variants in neuroblastoma-amplified sequence (NBAS) cause an autosomal recessive disorder with a wide range of symptoms affecting liver, skeletal system, and brain, among others. There is a continuously growing number of patients but a lack of systematic and quantitative analysis. METHODS: Individuals with biallelic variants in NBAS were recruited within an international, multicenter study, including novel and previously published patients. Clinical variables were analyzed with log-linear models and visualized by mosaic plots; facial profiles were investigated via DeepGestalt. The structure of the NBAS protein was predicted using computational methods. RESULTS: One hundred ten individuals from 97 families with biallelic pathogenic NBAS variants were identified, including 26 novel patients with 19 previously unreported variants, giving a total number of 86 variants. Protein modeling redefined the ß-propeller domain of NBAS. Based on the localization of missense variants and in-frame deletions, three clinical subgroups arise that differ significantly regarding main clinical features and are directly related to the affected region of the NBAS protein: ß-propeller (combined phenotype), Sec39 (infantile liver failure syndrome type 2/ILFS2), and C-terminal (short stature, optic atrophy, and Pelger-Huët anomaly/SOPH). CONCLUSION: We define clinical subgroups of NBAS-associated disease that can guide patient management and point to domain-specific functions of NBAS.

Severe SOPH syndrome due to a novel NBAS mutation in a 27-year-old woman-Review of this pleiotropic, autosomal recessive disorder: Mystery solved after two decades.

Autosomal recessive SOPH syndrome was first described in the Yakuts population of Asia by Maksimova et al. in 2010. It arises from biallelic pathogenic variants in the NBAS gene and is characterized by severe postnatal growth retardation, senile facial appearance, small hands and feet, optic atrophy with loss of visual acuity and color vision, and normal intelligence (OMIM #614800). The presence of Pelger-Hüet anomaly in this disorder led to its name as an acronym for Short stature, Optic nerve atrophy, and Pelger-Hüet anomaly. Recent publications have further contributed to the characterization of this syndrome through additional phenotype-genotype correlations. We review the clinical features described in these publications and report on a 27-year-old woman with dwarfism with osteolysis and multiple skeletal problems, minor anomalies, immunodeficiency, diabetes mellitus, and multiple secondary medical problems. Her condition was considered an unknown autosomal recessive disorder for many years until exome sequencing provided the diagnosis by revealing a founder disease-causing variant that was compound heterozygous with a novel pathogenic variant in NBAS. Based on the major clinical features of this individual and others reported earlier, a revision of the acronym is warranted to facilitate clinical recognition.

Infantile fever-triggered acute liver failure caused by novel neuroblastoma amplified sequence mutations: a case report.

BACKGROUND: Infantile liver failure syndrome-2 (ILFS2) is caused by neuroblastoma amplified sequence (NBAS) mutation. The disease is characterized by recurrent episodes of acute liver failure (ALF) or by liver crisis triggered by recurrent episodes of fever and complete recovery. CASE PRESENTATION: Here, we describe the case of a Chinese girl with typical clinical manifestation of ILFS2 without exhibition of extrahepatic involvement. The patient harbored novel compound heterozygous mutations in the NBAS region (c.3386C > T (p.Ser1129Phe), c.1A > C (p.Met1Leu) and c.875G > A (p.Gly292Glu)), mutations which have not been previously reported. After administration of antipyretics and intravenous glucose and electrolyte administration, the patient recovered fully. CONCLUSION: Through the present study, we recommend that ILFS2 should be taken into consideration during the differential diagnosis of children with recurrent, fever-triggered ALF. While the definitive diagnosis of ILFS2 remains dependent on genetic sequencing and discovery of NBAS, early antipyretic treatment is recommended to prevent liver crisis.

NBAS disease: 14 new patients, a recurrent mutation, and genotype-phenotype correlation among 24 Chinese patients.

AIM: Neuroblastoma amplified sequence (NBAS)-associated disease has a wide phenotypic spectrum, including infantile liver failure syndrome type 2 (ILFS2, OMIM #616483), short stature with optic nerve atrophy and Pelger-Huët anomaly (SOPH) syndrome (OMIM #614800), and a combined phenotype overlapping ILFS2 and SOPH syndrome. The mutation spectra of NBAS and its genotype-phenotype correlation among Chinese were not clear. METHODS: Clinical and genetic data were retrospectively collected from the medical charts of patients with biallelic NBAS mutations, as well as from Chinese patients in previously published reports. RESULTS: Fourteen new patients were identified, including 10 novel mutations: c.648-1G>A, c.2563_c.2577+5del/p.His855_Gln859del, c.3115C>T/p.Gln1039Ter, c.3284G>A/p.Trp1095Ter, c.2570C>T/p.Ala857Val, c.6859G>T/p.Asp2287Tyr, c.1028G>A/p.Ser343Asn, c.1177_1182delinsAGATAGA/p.Val393ArgfsTer2, c.3432_3435dupCAGT/p.Ala1146GlnfsTer14, and c.680_690dupACTGTTTCAGC/p.Phe231ThrfsTer35. All 14 patients presented as fever-triggered liver injury, including nine patients that satisfied the criteria of acute liver failure (ALF) in whom c.3596G>A/p.Cys1199Tyr occurred five times. Nine patients had extrahepatic manifestations including short stature, skeletal abnormalities, intellectual disability, ophthalmic abnormalities, low levels of serum immunoglobulins, facial dysmorphism, and cardiac abnormalities. Ten other Chinese patients were collected through a review of published works. Genotype-phenotype analysis in 24 Chinese patients revealed that the percentage of ALF patients with variants in the Sec39 domain was significantly higher than that in the C-terminal (100% vs. 12.5%, P = 0.000), and the percentage of multi-organ/system involvement in patients with variants in the Sec39 domain was significantly lower than that in the C-terminal (40% vs. 100%, P = 0.0128). CONCLUSIONS: We reported 14 new patients, 10 novel mutations, and a unique recurrent mutation. Correlation analysis indicated that the domain of missense and non-frameshift insertion/deletion mutations in NBAS protein is related to phenotype among Chinese patients.

NBAS pathogenic variants: Defining the associated clinical and facial phenotype and genotype-phenotype correlations.

The pathogenic variants in the neuroblastoma-amplified sequence (NBAS) are associated with a clinical spectrum involving the hepatic, skeletal, ocular, and immune systems. Here, we report on two unrelated subjects with a complex phenotype solved by whole-exome sequencing, who shared a synonymous change in NBAS that was documented to affect the transcript processing and co-occurring with a truncating change. Starting from these two cases, we systematically assessed the clinical information available for all subjects with biallelic NBAS pathogenic variants (73 cases in total). We revealed a recognizable facial profile (hypotelorism, thin lips, pointed chin, and "progeroid" appearance) determined by using DeepGestalt facial recognition technology, and we provide evidence for the occurrence of genotype-phenotype correlations. Notably, severe hepatic involvement was associated with variants affecting the NBAS-Nter and Sec39 domains, whereas milder liver involvement and immunodeficiency were generally associated with variants located at the N-terminus and C-terminus of the protein. Remarkably, no patient was reported to carry two nonsense variants, suggesting lethality of complete NBAS loss-of-function.

Novel NBAS mutations and fever-related recurrent acute liver failure in Chinese children: a retrospective study.

BACKGROUND: Underlying causes in Chinese children with recurrent acute liver failure (RALF), including liver crises less than full acute liver failure, are incompletely understood. We sought to address this by searching for genes mutated in such children. METHODS: Five unrelated Chinese boys presenting between 2012 and 2015 with RALF of unexplained etiology were studied. Results of whole exome sequencing were screened for mutations in candidate genes. Mutations were verified in patients and their family members by Sanger sequencing. All 5 boys underwent liver biopsy. RESULTS: NBAS was the only candidate gene mutated in more than one patient (biallelic mutations, 3 of 5 patients; 5 separate mutations). All NBAS mutations were novel and predictedly pathogenic (frameshift insertion mutation c.6611_6612insCA, missense mutations c.2407G > A and c.3596G > A, nonsense mutation c.586C > T, and splicing-site mutation c.5389 + 1G > T). Of these mutations, 3 lay in distal (C-terminal) regions of NBAS, a novel distribution. Unlike the 2 patients without NBAS mutations, the 3 patients with confirmed NBAS mutations all suffered from a febrile illness before each episode of liver crisis (fever-related RALF), with markedly elevated alanine aminotransferase and aspartate aminotransferase activities 24-72 h after elevation of body temperature, succeeded by severe coagulopathy and mild to moderate jaundice. CONCLUSIONS: As in other countries, so too in China; NBAS disease is a major cause of fever-related RALF in children. The mutation spectrum of NBAS in Chinese children seems different from that described in other populations.

NBAS mutations cause a multisystem disorder involving bone, connective tissue, liver, immune system, and retina.

We report two unrelated patients with a multisystem disease involving liver, eye, immune system, connective tissue, and bone, caused by biallelic mutations in the neuroblastoma amplified sequence (NBAS) gene. Both presented as infants with recurrent episodes triggered by fever with vomiting, dehydration, and elevated transaminases. They had frequent infections, hypogammaglobulinemia, reduced natural killer cells, and the Pelger-Huët anomaly of their granulocytes. Their facial features were similar with a pointed chin and proptosis; loose skin and reduced subcutaneous fat gave them a progeroid appearance. Skeletal features included short stature, slender bones, epiphyseal dysplasia with multiple phalangeal pseudo-epiphyses, and small C1-C2 vertebrae causing cervical instability and myelopathy. Retinal dystrophy and optic atrophy were present in one patient. NBAS is a component of the synthaxin-18 complex and is involved in nonsense-mediated mRNA decay control. Putative loss-of-function mutations in NBAS are already known to cause disease in humans. A specific founder mutation has been associated with short stature, optic nerve atrophy and Pelger-Huët anomaly of granulocytes (SOPH) in the Siberian Yakut population. A more recent report associates NBAS mutations with recurrent acute liver failure in infancy in a group of patients of European descent. Our observations indicate that the phenotypic spectrum of NBAS deficiency is wider than previously known and includes skeletal, hepatic, metabolic, and immunologic aspects. Early recognition of the skeletal phenotype is important for preventive management of cervical instability.