Severe syndromic ID and skewed X-inactivation in a girl with NAA10 dysfunction and a novel heterozygous de novo NAA10 p.(His16Pro) variant - a case report

The Cardiovascular Manifestations and Management Recommendations for Ogden Syndrome

The NatA complex is composed of the NAA10, NAA15, and HYPK sub-units. It is primarily responsible for N-terminal acetylation, a critical post-translational modification in eukaryotes. Pathogenic variants within NAA10 cause Ogden Syndrome (OS), which is characterized by varying degrees of intellectual disability, hypotonia, developmental delay, and cardiac abnormalities. Although the cardiac manifestations of the disease have been described extensively in case reports, there has not been a study focusing on the cardiac manifestations and their recommended clinical cardiac management. In this study, we describe the cardiac manifestations of OS in a cohort of 85 probands. We found increased incidence of structural and electrophysiologic abnormalities, with particularly high prevalence of QT interval prolongation. Sub-analysis showed that male probands and those with variants within the NAA15-binding domain had more severe phenotypes than females or those with variants outside of the NAA15-binding domain. Our results suggest that an OS diagnosis should be accompanied by full cardiac workup with emphasis on echocardiogram for structural defects and EKG/Holter monitoring for electrophysiologic abnormalities. Additionally, we strongly recommend that the use of QT-prolonging drugs be followed up with routine electrophysiological monitoring or consultation with a pediatric cardiologist. We hope this study guides clinicians and caregivers treating patients with OS and moves the field toward a standardized diagnostic workup for patients with this condition.

Dysregulation of N-terminal acetylation causes cardiac arrhythmia and cardiomyopathy

N-terminal acetyltransferases including NAA10 catalyze N-terminal acetylation, an evolutionarily conserved co- and post-translational modification. However, little is known about the role of N-terminal acetylation in cardiac homeostasis. To gain insight into cardiac-dependent NAA10 function, we studied a previously unidentified NAA10 variant p.(Arg4Ser) segregating with QT-prolongation, cardiomyopathy, and developmental delay in a large kindred. Here, we show that the NAA10R4S variant reduced enzymatic activity, decreased NAA10-NAA15 complex formation, and destabilized the enzymatic complex N-terminal acetyltransferase A. In NAA10R4S/Y-induced pluripotent stem-cell-derived cardiomyocytes (iPSC-CMs), dysregulation of the late sodium and slow delayed rectifier potassium currents caused severe repolarization abnormalities, consistent with clinical QT prolongation. Engineered heart tissues generated from NAA10R4S/Y-iPSC-CMs had significantly decreased contractile force and sarcomeric disorganization, consistent with the pedigree's cardiomyopathic phenotype. Proteomic studies revealed dysregulation of metabolic pathways and cardiac structural proteins. We identified small molecule and genetic therapies that normalized the phenotype of NAA10R4S/Y-iPSC-CMs. Our study defines the roles of N-terminal acetylation in cardiac regulation and delineates mechanisms underlying QT prolongation, arrhythmia, and cardiomyopathy caused by NAA10 dysfunction.

Neuroanatomical features of NAA10 and NAA15-related neurodevelopmental syndromes

BACKGROUND

NAA10-related and NAA15-related neurodevelopmental (ND) syndromes present with intellectual disability, hypotonia, cardiac abnormalities, and delayed development. While data exists on the clinical manifestations of these conditions, there are few reports describing the neuroanatomical abnormalities present on imaging.

OBJECTIVE

We aim to provide neuroimaging analyses for a subset of probands with NAA10- and NAA15-related neurodevelopmental symptoms and assess the severity and number of neuroanatomical anomalies and their associated functional impairments to better understand the pathophysiology of these disease processes.

MATERIALS AND METHODS

Neuroimaging studies were obtained from 26 probands (18 with pathogenic variants in NAA10, 8 with pathogenic variants in NAA15) and evaluated. In depth medical histories were also collected on probands, including genetic testing results and developmental history. The Vineland 3 Adaptive Behavior Scale was also administered to assess functional status of the probands.

RESULTS

On average, individuals with NAA10-related ND syndrome had 5.7 anatomical abnormalities (standard deviation (SD) = 3.0), whereas those with NAA15-related ND syndrome had 2.8 (SD = 2.3, p = 0.02). Probands with a greater number of anatomical abnormalities tended to score worse on Vineland assessments. Structure and function were correlated such that individuals with greater defects on, for example, motor regions of their scans, tested worse on motor portions of the Vineland. Probands followed longitudinally demonstrated several changes between scans, most commonly in the cerebellum, brainstem, and degree of myelination. Such changes were only observed for probands with NAA10-related ND syndrome.

CONCLUSION

This analysis of a cohort of probands with NAA10-related ND syndrome and NAA15-related ND syndrome by two neuroradiologists has established a range of subtle abnormalities. We hope these findings guide future research and diagnostic studies for this population.

The Cardiovascular Manifestations and Management Recommendations for Ogden Syndrome

The NatA complex is composed of the NAA10, NAA15, and HYPK subunits. It is primarily responsible for N-terminal acetylation, a critical post-translational modification in eukaryotes. Pathogenic variants within NAA10 cause Ogden Syndrome (OS), which is characterized by varying degrees of intellectual disability, hypotonia, developmental delay, and cardiac abnormalities. Although the cardiac manifestations of the disease have been described extensively in case reports, there has not been a study focusing on the cardiac manifestations and their recommended clinical cardiac management. In this study, we describe the cardiac manifestations of OS in a cohort of 85 probands. We found increased incidence of structural and electrophysiologic abnormalities, with particularly high prevalence of QT interval prolongation. Sub-analysis showed that male probands and those with variants within the NAA15-binding domain had more severe phenotypes than females or those with variants outside of the NAA15-binding domain. Our results suggest that an OS diagnosis should be accompanied by full cardiac workup with emphasis on echocardiogram for structural defects and EKG/Holter monitoring for electrophysiologic abnormalities. Additionally, we strongly recommend that the use of QT-prolonging drugs be followed up with routine electrophysiological monitoring or consultation with a pediatric cardiologist. We hope this study guides clinicians and caregivers treating patients with OS and moves the field toward a standardized diagnostic workup for patients with this condition.

Conformational plasticity links structural instability of NAA10F128I and NAA10F128L mutants to their catalytic deregulation

The acetylation of proteins' N-terminal amino groups by the N-acetyltransferase complexes plays a crucial role in modulating the spatial stability and functional activities of diverse human proteins. Mutations disrupting the stability and function of NAA10 result in X-linked rare genetic disorders. In this study, we conducted a global analysis of the impact of fifteen disease-associated missense mutations in NAA10. The analyses revealed that mutations in specific residues, such as Y43, V107, V111, and F128, predictably disrupted interactions essential for NAA10 stability, while most mutations (except R79C, A111W, Q129P, and N178K) expectedly led to structural destabilization. Mutations in many conserved residues within short linear motifs and post-translational modification sites were predicted to affect NAA10 functionality and regulation. All mutations were classified as pathogenic, with F128I and F128L identified as the most destabilizing mutations. The findings show that the F128L and F128I mutations employ different mechanisms for the loss of catalytic activities of NAA10F128L and NAA10F128I due to their structural instability. These two mutations induce distinct folding energy states that differentially modulate the structures of different regions of NAA10F128L and NAA10F128I. Specifically, the predicted instability caused by the F128I mutation results in decreased flexibility within the substrate-binding region, impairing the substrate peptide binding ability of NAA10F128I. Conversely, F128L is predicted to reduce the flexibility of the region containing the acetyl-CoA binding residues in NAA10F128L. Our study provides insights into the mechanism of catalytic inactivation of mutants of NAA10, particularly elucidating the mechanistic features of the structural and functional pathogenicity of the F128L and F128I mutations.

A repository of Ogden syndrome patient derived iPSC lines and isogenic pairs by X-chromosome screening and genome-editing

Amino-terminal (Nt-) acetylation (NTA) is a common protein modification, affecting 80% of cytosolic proteins in humans. The human essential gene, NAA10, encodes the enzyme NAA10, as the catalytic subunit for the N-terminal acetyltransferase A (NatA) complex, including the accessory protein, NAA15. The first human disease directly involving NAA10 was discovered in 2011, and it was named Ogden syndrome (OS), after the location of the first affected family residing in Ogden, Utah, USA. Since that time, other variants have been found in NAA10 and NAA15. Here we describe the generation of 31 iPSC lines, with 16 from females and 15 from males. This cohort includes CRISPR-mediated correction to the wild-type genotype in 4 male lines, along with editing one female line to generate homozygous wild-type or mutant clones. Following the monoclonalizaiton and screening for X-chromosome activation status in female lines, 3 additional pairs of female lines, in which either the wild type allele is on the active X chromosome (Xa) or the pathogenic variant allele is on Xa, have been generated. Subsets of this cohort have been successfully used to make cardiomyocytes and neural progenitor cells (NPCs). These cell lines are made available to the community via the NYSCF Repository.

Longitudinal adaptive behavioral outcomes in Ogden syndrome by seizure status and therapeutic intervention

Ogden syndrome, also known as NAA10-related neurodevelopmental syndrome, is a rare genetic condition associated with pathogenic variants in the NAA10 N-terminal acetylation family of proteins. The condition was initially described in 2011 and is characterized by a range of neurologic symptoms, including intellectual disability and seizures, as well as developmental delays, psychiatric symptoms, congenital heart abnormalities, hypotonia, and others. Previously published articles have described the etiology and phenotype of Ogden syndrome, mostly with retrospective analyses; herein, we report prospective data concerning its progress over time. The current study involves a total of 58 distinct participants; of these, 43 caregivers were interviewed using the Vineland-3 and answered a survey regarding therapy and other questions, 10 of whom completed the Vineland-3 but did not answer the survey, and 5 participants who answered the survey but have not yet performed the Vineland-3 due to language constraints. The average age at the time of the most recent assessment was 12.4 years, with individuals ranging in age from 11 months to 40.2 years. Using Vineland-3 scores, we show decline in cognitive function over time in individuals with Ogden syndrome (n = 53). Sub-domain analysis found the decline to be present across all modalities. In addition, we describe the nature of seizures in this condition in greater detail, as well as investigate how already-available non-pharmaceutical therapies impact individuals with NAA10-related neurodevelopmental syndrome. Additional investigation between seizure and non-seizure groups showed no significant difference in adaptive behavior outcomes. A therapy investigation showed speech therapy to be the most commonly used therapy by individuals with NAA10-related neurodevelopmental syndrome, followed by occupational and physical therapy, with more severely affected individuals receiving more types of therapy than their less-severe counterparts. Early intervention analysis was only significantly effective for speech therapy, with analyses of all other therapies being non-significant. Our study portrays the decline in cognitive function over time of individuals within our cohort, independent of seizure status, and therapies being received, and highlights the urgent need for the development of effective treatments for Ogden syndrome.

NAC guides a ribosomal multienzyme complex for nascent protein processing

Approximately 40% of the mammalian proteome undergoes N-terminal methionine excision and acetylation, mediated sequentially by methionine aminopeptidase (MetAP) and N-acetyltransferase A (NatA), respectively1. Both modifications are strictly cotranslational and essential in higher eukaryotic organisms1. The interaction, activity and regulation of these enzymes on translating ribosomes are poorly understood. Here we perform biochemical, structural and in vivo studies to demonstrate that the nascent polypeptide-associated complex2,3 (NAC) orchestrates the action of these enzymes. NAC assembles a multienzyme complex with MetAP1 and NatA early during translation and pre-positions the active sites of both enzymes for timely sequential processing of the nascent protein. NAC further releases the inhibitory interactions from the NatA regulatory protein huntingtin yeast two-hybrid protein K4,5 (HYPK) to activate NatA on the ribosome, enforcing cotranslational N-terminal acetylation. Our results provide a mechanistic model for the cotranslational processing of proteins in eukaryotic cells.

A Natural History of NAA15 -related Neurodevelopmental Disorder Through Adolescence

NAA15 is a member of the NatA N-terminal acetyltransferase complex, which also includes the NAA10 enzymatic sub-unit. Individuals with variants in the NAA15 coding region develop NAA15 -related neurodevelopmental syndrome, which presents with a wide array of manifestations that affect the heart, brain, musculoskeletal system, and behavioral and cognitive development. We tracked a cohort of 27 participants (9 females and 18 males) over time, each with a pathogenic NAA15 variant, and administered the Vineland-3 assessment to assess their adaptive functioning. We found that the cohort performed significantly worse compared to the normalized Vineland values. On average, females performed better than males, and they performed significantly better on the Motor Domain and Fine Motor Sub-Domain portions of the assessment. Over time, females showed a decrease in adaptive functioning, with the decline being especially correlated at the Coping, Domestic, and Fine motor sub-domains. Males (after excluding one outlier) showed a moderate positive correlation between age and ABC standard score. Ultimately, additional longitudinal data should be collected to determine the validity of the between sex-differences and to better understand the change in adaptive behavioral outcomes of individuals with NAA15 -neurodevelopmental disorder as they age.

Dysregulation of N-terminal acetylation causes cardiac arrhythmia and cardiomyopathy

N-terminal-acetyltransferases including NAA10 catalyze N-terminal acetylation (Nt-acetylation), an evolutionarily conserved co-translational modification. Little is known about the role of Nt-acetylation in cardiac homeostasis. To gain insights, we studied a novel NAA10 variant (p.R4S) segregating with QT-prolongation, cardiomyopathy and developmental delay in a large kindred. Here we show that the NAA10-R4S mutation reduced enzymatic activity, decreased expression levels of NAA10/NAA15 proteins, and destabilized the enzymatic complex NatA. In NAA10R4S/Y-iPSC-CMs, dysregulation of the late sodium and slow rectifying potassium currents caused severe repolarization abnormalities, consistent with clinical QT prolongation. Engineered heart tissues generated from NAA10R4S/Y-iPSC-CMs had significantly decreased contractile force and sarcomeric disorganization, consistent with the pedigree's cardiomyopathic phenotype. We identified small molecule and genetic therapies that normalized the phenotype of NAA10R4S/Y-iPSC-CMs. Our study defines novel roles of Nt-acetylation in cardiac regulation and delineates mechanisms underlying QT prolongation, arrhythmia, and cardiomyopathy caused by NAA10 dysfunction.

Neuroanatomical Features of NAA10- and NAA15-Related Neurodevelopmental Syndromes

Background

NAA10-related (Ogden Syndrome) and NAA15-related neurodevelopmental syndromes present with varying degrees of intellectual disability, hypotonia, congenital cardiac abnormalities, seizures, and delayed speech and motor development. While there is much data on the clinical manifestations of these conditions, there are few radiologic reports describing the neuroanatomical abnormalities present on imaging.

Objective

Our goal was to provide neuroimaging analyses for a subset of probands with NAA10- and NAA15-related neurodevelopmental symptoms and assess severity, common radiologic anomalies, and changes over time to better understand the pathophysiology of these disease processes.

Materials and Methods

Neuroimaging studies from 26 probands (18 with pathogenic variants in NAA10, 8 with pathogenic variants in NAA15) were collected and analyzed. Size of the cerebrum, brainstem, and cerebellum, as well as myelination, brain malformations, globus pallidus hyperintensity, brain lesions, 4th ventricle size, tegmentovermian angle, cisterna magna size, pituitary size, olfactory tract, palate arch, and choroid plexus abnormalities were analyzed. In depth medical histories were also collected on all probands, including genetic testing results and social, cognitive, and developmental history. The Vineland 3 Adaptive Behavior Scale was also administered to the parents to assess functional status of the probands.

Results

On average, individuals with Ogden Syndrome had 5.7 anatomical abnormalities (standard deviation (SD) = 3.0), whereas those with NAA15 related neurodevelopmental syndrome had 2.8 (SD = 2.3) (p = .02). Probands who had more anatomical abnormalities tended to score worse on Vineland assessments, suggesting a possible correlation between the two. Structural-functional anatomic differences seen were preserved such that individuals with greater defects on, for example, motor regions of their scans tested worse on motor portions of the Vineland. Probands followed longitudinally demonstrated several changes between scans, most commonly in the cerebellum, brainstem, and degree of myelination. Such changes were only observed for probands with NAA10 variants in our cohort.

Conclusion

Despite clinical imaging being reported as being predominantly "normal" during routine clinical care, this analysis of a cohort of patients with NAA10-related (Ogden Syndrome) and NAA15-related neurodevelopmental syndrome by one neuroradiologist has established a range of subtle abnormalities. We hope these findings guide future research and diagnostic studies for this patient population.

Evaluating possible maternal effect lethality and genetic background effects in Naa10 knockout mice

Amino-terminal (Nt-) acetylation (NTA) is a common protein modification, affecting approximately 80% of all human proteins. The human essential X-linked gene, NAA10, encodes for the enzyme NAA10, which is the catalytic subunit in the N-terminal acetyltransferase A (NatA) complex. There is extensive genetic variation in humans with missense, splice-site, and C-terminal frameshift variants in NAA10. In mice, Naa10 is not an essential gene, as there exists a paralogous gene, Naa12, that substantially rescues Naa10 knockout mice from embryonic lethality, whereas double knockouts (Naa10-/Y Naa12-/-) are embryonic lethal. However, the phenotypic variability in the mice is nonetheless quite extensive, including piebaldism, skeletal defects, small size, hydrocephaly, hydronephrosis, and neonatal lethality. Here we replicate these phenotypes with new genetic alleles in mice, but we demonstrate their modulation by genetic background and environmental effects. We cannot replicate a prior report of "maternal effect lethality" for heterozygous Naa10-/X female mice, but we do observe a small amount of embryonic lethality in the Naa10-/y male mice on the inbred genetic background in this different animal facility.

Longitudinal Adaptive Behavioral Outcomes in Ogden Syndrome by Seizure Status and Therapeutic Intervention

Ogden syndrome, also known as NAA10-related neurodevelopmental syndrome, is a rare genetic condition associated with pathogenic variants in the NAA10 N-terminal acetylation family of proteins. The condition was initially described in 2011, and is characterized by a range of neurologic symptoms, including intellectual disability and seizures, as well as developmental delays, psychiatric symptoms, congenital heart abnormalities, hypotonia and others. Previously published articles have described the etiology and phenotype of Ogden syndrome, mostly with retrospective analyses; herein, we report prospective data concerning its progress over time. Additionally, we describe the nature of seizures in this condition in greater detail, as well as investigate how already-available non-pharmaceutical therapies impact individuals with NAA10-related neurodevelopmental syndrome. Using Vineland-3 scores, we show decline in cognitive function over time in individuals with Ogden syndrome. Sub-domain analysis found the decline to be present across all modalities. Additional investigation between seizure and non-seizure groups showed no significant difference in adaptive behavior outcomes. Therapy investigation showed speech therapy to be the most commonly used therapy by individuals with NAA10-related neurodevelopmental syndrome, followed by occupational and physical therapy. with more severely affected individuals receiving more types of therapy than their less-severe counterparts. Early intervention analysis was only significantly effective for speech therapy, with analyses of all other therapies being non-significant. Our study portrays the decline in cognitive function over time of individuals within our cohort, independent of seizure status and therapies being received, and highlights the urgent need for the development of effective treatments for Ogden syndrome.

Evaluating possible maternal effect lethality and genetic background effects in Naa10 knockout mice

Amino-terminal (Nt-) acetylation (NTA) is a common protein modification, affecting approximately 80% of all human proteins. The human essential X-linked gene, NAA10, encodes for the enzyme NAA10, which is the catalytic subunit in the N-terminal acetyltransferase A (NatA) complex. There is extensive genetic variation in humans with missense, splice-site, and C-terminal frameshift variants in NAA10. In mice, Naa10 is not an essential gene, as there exists a paralogous gene, Naa12, that substantially rescues Naa10 knockout mice from embryonic lethality, whereas double knockouts (Naa10-/Y Naa12-/-) are embryonic lethal. However, the phenotypic variability in the mice is nonetheless quite extensive, including piebaldism, skeletal defects, small size, hydrocephaly, hydronephrosis, and neonatal lethality. Here we replicate these phenotypes with new genetic alleles in mice, but we demonstrate their modulation by genetic background and environmental effects. We cannot replicate a prior report of "maternal effect lethality" for heterozygous Naa10-/X female mice, but we do observe a small amount of embryonic lethality in the Naa10-/Y male mice on the inbred genetic background in this different animal facility.

Expanding the phenotypic spectrum of NAA10-related neurodevelopmental syndrome and NAA15-related neurodevelopmental syndrome

Amino-terminal (Nt-) acetylation (NTA) is a common protein modification, affecting 80% of cytosolic proteins in humans. The human essential gene, NAA10, encodes for the enzyme NAA10, which is the catalytic subunit in the N-terminal acetyltransferase A (NatA) complex, also including the accessory protein, NAA15. The full spectrum of human genetic variation in this pathway is currently unknown. Here we reveal the genetic landscape of variation in NAA10 and NAA15 in humans. Through a genotype-first approach, one clinician interviewed the parents of 56 individuals with NAA10 variants and 19 individuals with NAA15 variants, which were added to all known cases (N = 106 for NAA10 and N = 66 for NAA15). Although there is clinical overlap between the two syndromes, functional assessment demonstrates that the overall level of functioning for the probands with NAA10 variants is significantly lower than the probands with NAA15 variants. The phenotypic spectrum includes variable levels of intellectual disability, delayed milestones, autism spectrum disorder, craniofacial dysmorphology, cardiac anomalies, seizures, and visual abnormalities (including cortical visual impairment and microphthalmia). One female with the p.Arg83Cys variant and one female with an NAA15 frameshift variant both have microphthalmia. The frameshift variants located toward the C-terminal end of NAA10 have much less impact on overall functioning, whereas the females with the p.Arg83Cys missense in NAA10 have substantial impairment. The overall data are consistent with a phenotypic spectrum for these alleles, involving multiple organ systems, thus revealing the widespread effect of alterations of the NTA pathway in humans.

Clinical manifestations in a Chinese girl with heterozygous de novo NAA10 variant c. 247C > T, p. (Arg83Cys): a case report

The NAA10 gene encodes the catalytic subunit of the N-terminal acetyltransferase protein complex A (NatA), which is supposed to acetylate approximately 40% of the human proteins. After the advent of next-generation sequencing, more variants in the NAA10 gene and Ogden syndrome (OMIM# 300855) have been reported. Individuals with NAA10-related syndrome have a wide spectrum of clinical manifestations and the genotype-phenotype correlation is still far from being confirmed. Here, we report a three years old Chinese girl carrying a heterozygous de novo NAA10 [NM_003491: c. 247C > T, p. (Arg83Cys)] variant (dbSNP# rs387906701) (ClinVar# 208664) (OMIM# 300013.0010). The proband not only has some mild and common clinical manifestations, including dysmorphic features, developmental delay, obstructive hypertrophic cardiomyopathy, and arrhythmia, but also shows some rare clinical features such as exophthalmos, blue sclera, cutaneous capillary malformations, and adenoid hypertrophy. Our attempt is to expand the clinical phenotype associated with NAA10-related syndrome and explore genotype-phenotype correlation with such syndrome.

Phenotypic variability and gastrointestinal manifestations/interventions for growth in NAA10-related neurodevelopmental syndrome

Our study of 61 children with NAA10-related neurodevelopmental syndrome, an X-linked disorder due to NAA10 gene variants, demonstrated a high prevalence of growth failure, with weight and height percentiles often in the failure-to-thrive diagnostic range; however, dramatic weight fluctuations and phenotypic variability is evidenced in the growth parameters of this population. Although never previously explored in depth, the gastrointestinal pathology associated with NAA10-related neurodevelopmental syndrome includes feeding difficulties in infancy, dysphagia, GERD/silent reflux, vomiting, constipation, diarrhea, bowel incontinence, and presence of eosinophils on esophageal endoscopy, in order from most to least prevalent. Additionally, the gastrointestinal symptom profile for children with this syndrome has been expanded to include eosinophilic esophagitis, cyclic vomiting syndrome, Mallory Weiss tears, abdominal migraine, esophageal dilation, and subglottic stenosis. Although the exact cause of poor growth in NAA10-related neurodevelopmental syndrome probands is unclear and the degree of contribution to this problem by GI symptomatology remains uncertain, an analysis including nine G-tube or GJ-tube fed probands demonstrates that G/GJ-tubes are overall efficacious with respect to improvements in weight gain and caregiving. The choice to insert a gastrostomy or gastrojejunal tube to aid with weight gain is often a challenging decision to make for parents, who may alternatively choose to rely on oral feeding, caloric supplementation, calorie tracking, and feeding therapy. In this case, if NAA10-related neurodevelopmental syndrome children are not tracking above the failure to thrive (FTT) range past 1 year of age despite such efforts, the treating physicians should be consulted regarding possibly undergoing G-tube placement to avoid prolonged growth failure. If G-tubes are not immediately inducing weight gain after insertion, recommendations could include altering formula, increasing caloric input, or exchanging a G-tube for a GJ-tube by means of a minimally invasive procedure.

Biochemical analysis of novel NAA10 variants suggests distinct pathogenic mechanisms involving impaired protein N-terminal acetylation

NAA10 is the catalytic subunit of the N-terminal acetyltransferase complex, NatA, which is responsible for N-terminal acetylation of nearly half the human proteome. Since 2011, at least 21 different NAA10 missense variants have been reported as pathogenic in humans. The clinical features associated with this X-linked condition vary, but commonly described features include developmental delay, intellectual disability, cardiac anomalies, brain abnormalities, facial dysmorphism and/or visual impairment. Here, we present eight individuals from five families with five different de novo or inherited NAA10 variants. In order to determine their pathogenicity, we have performed biochemical characterisation of the four novel variants c.16G>C p.(A6P), c.235C>T p.(R79C), c.386A>C p.(Q129P) and c.469G>A p.(E157K). Additionally, we clinically describe one new case with a previously identified pathogenic variant, c.384T>G p.(F128L). Our study provides important insight into how different NAA10 missense variants impact distinct biochemical functions of NAA10 involving the ability of NAA10 to perform N-terminal acetylation. These investigations may partially explain the phenotypic variability in affected individuals and emphasise the complexity of the cellular pathways downstream of NAA10.

Hydroxylation of the Acetyltransferase NAA10 Trp38 Is Not an Enzyme-Switch in Human Cells

NAA10 is a major N-terminal acetyltransferase (NAT) that catalyzes the cotranslational N-terminal (Nt-) acetylation of 40% of the human proteome. Several reports of lysine acetyltransferase (KAT) activity by NAA10 exist, but others have not been able to find any NAA10-derived KAT activity, the latter of which is supported by structural studies. The KAT activity of NAA10 towards hypoxia-inducible factor 1α (HIF-1α) was recently found to depend on the hydroxylation at Trp38 of NAA10 by factor inhibiting HIF-1α (FIH). In contrast, we could not detect hydroxylation of Trp38 of NAA10 in several human cell lines and found no evidence that NAA10 interacts with or is regulated by FIH. Our data suggest that NAA10 Trp38 hydroxylation is not a switch in human cells and that it alters its catalytic activity from a NAT to a KAT.

Clinical Manifestations in a Girl with NAA10-Related Syndrome and Genotype-Phenotype Correlation in Females

Since 2011, eight males with an X-linked recessive disorder (Ogden syndrome, MIM #300855) associated with the same missense variant p.(Ser37Pro) in the NAA10 gene have been described. After the advent of whole exome sequencing, many NAA10 variants have been reported as causative of syndromic or non-syndromic intellectual disability in both males and females. The NAA10 gene lies in the Xq28 region and encodes the catalytic subunit of the major N-terminal acetyltransferase complex NatA, which acetylates almost half the human proteome. Here, we present a young female carrying a de novo NAA10 [NM_003491:c.247C > T, p.(Arg83Cys)] variant. The 18-year-old girl has severely delayed motor and language development, autistic traits, postnatal growth failure, facial dysmorphisms, interventricular septal defect, neuroimaging anomalies and epilepsy. Our attempt is to expand and compare genotype–phenotype correlation in females with NAA10-related syndrome. A detailed clinical description could have relevant consequences for the clinical management of known and newly identified individuals.

Confirmation of Ogden syndrome as an X-linked recessive fatal disorder due to a recurrent NAA10 variant and review of the literature

Ogden syndrome is a rare lethal X‐linked recessive disorder caused by a recurrent missense variant (Ser37Pro) in the NAA10 gene, encoding the catalytic subunit of the N‐terminal acetyltransferase A complex (NatA). So far eight boys of two different families have been described in the literature, all presenting the distinctive and recognizable phenotype, which includes mostly postnatal growth retardation, global severe developmental delay, characteristic craniofacial features, and structural cardiac anomalies and/or arrhythmias. Here, we report the ninth case of Ogden syndrome with an independent recurrence of the Ser37Pro variant. We were able to follow the clinical course of the affected boy and delineate the evolving phenotype from his birth until his unfortunate death at 7 months. We could confirm the associated phenotype as well as the natural history of this severe disease. By describing new presenting features, we are further expanding the clinical spectrum associated with Ogden syndrome and review other phenotypes associated with NAA10 variants.

NAA10 p.(D10G) and NAA10 p.(L11R) Variants Hamper Formation of the NatA N-Terminal Acetyltransferase Complex

The majority of the human proteome is subjected to N-terminal (Nt) acetylation catalysed by N-terminal acetyltransferases (NATs). The NatA complex is composed of two core subunits—the catalytic subunit NAA10 and the ribosomal anchor NAA15. Furthermore, NAA10 may also have catalytic and non-catalytic roles independent of NatA. Several inherited and de novo NAA10 variants have been associated with genetic disease in humans. In this study, we present a functional analysis of two de novo NAA10 variants, c.29A>G p.(D10G) and c.32T>G p.(L11R), previously identified in a male and a female, respectively. Both of these neighbouring amino acids are highly conserved in NAA10. Immunoprecipitation experiments revealed that both variants hamper complex formation with NAA15 and are thus likely to impair NatA-mediated Nt-acetylation in vivo. Despite their common impact on NatA formation, in vitro Nt-acetylation assays showed that the variants had opposing impacts on NAA10 catalytic activity. While NAA10 c.29A>G p.(D10G) exhibits normal intrinsic NatA activity and reduced monomeric NAA10 NAT activity, NAA10 c.32T>G p.(L11R) displays reduced NatA activity and normal NAA10 NAT activity. This study expands the scope of research into the functional consequences of NAA10 variants and underlines the importance of understanding the diverse cellular roles of NAA10 in disease mechanisms.