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

Abstract 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.


| INTRODUCTION
Ogden syndrome, was named after the hometown of the first family observed by John M. Opitz with an X-linked recessive disorder characterized by early lethality due to structural cardiac anomalies and/or arrhythmias, severe global developmental delay, postnatal growth retardation, and prematurely aged appearance with reduced subcutaneous adipose tissue and redundant skin (Lyon, 2011;Maffly, 2012;Rope et al., 2011;Wu & Lyon, 2018). In 2011, it was identified as the first human genetic disorder associated with a variant in an N-terminal acetyltransferase (NAT) (Rope et al., 2011). So far, only the original eight affected males from two different families are described in the literature, all harboring the same missense variant, a Ser37Pro, in the gene encoding NAA10, the catalytic subunit of the N-terminal acetyltransferase A complex (NatA), the major human NAT involved in the co-translational acetylation of proteins (Arnesen et al., 2005;Rope et al., 2011). Nevertheless, further phenotypes in males and females have been described with other pathogenic variants resulting in the suggestion of the broader term NAA10-related syndrome (Wu & Lyon, 2018). We now report an independent recurrence of the Ser37Pro variant further supporting the initially described genotype-phenotype relation with the Ogden syndrome clinical course and also expanding its clinical signs.

| CLINICAL REPORT
This male infant was born to healthy, non-consanguineous parents of German and Polish origin. He was the first child of the 40-year-old mother, who had one miscarriage before. The mother had no obvious anomalies, has a high educational attainment (University degrees in economics and psychology), and runs her own business. Paternal age at birth was 57 and his history was unremarkable. The pregnancy was complicated by intrauterine growth retardation (IUGR). An abnormal cardiotocography (CTG) lead to the induction of labor at gestational week 37. His birth weight was 2580 g (À1SD), his birth length was 43 cm (À3SD), and his occipital frontal circumference measured 32.5 cm (À1SD). Apgar scores were 9/9/10. The neonatal examination revealed severe muscular hypotonia and a number of distinctive morphologic signs, in particular the progeroid facial appearance. After 48 h, he was transferred to the neonatal intensive care unit (NICU) because of respiratory distress, feeding difficulties, and hyperbilirubinemia. Clinical genetic evaluation of the 3-day-old boy showed facial wrinkling and hirsutism, extension of hair growth on temples to lateral eyebrow, prominent eyes, short and down-slanting palpebral fissures, apparent hypertelorism, wide nasal bridge, prominent nose, short columella, wide philtrum and mouth, high, narrow palate, thick lingual frenulum, gingival overgrowth, thin upper lip vermilion in frontal view and microretrognathia. The ears were large, low-set, posteriorly rotated and dysplastic with prominent crus of helix and a large earlobe. In addition, a stenosis of the external F I G U R E 1 Prenatal ultrasound scans (a-c) and pictures of our patient at 3 days (d-j), 4 (k and l), and 6 months (m-n) showing the facial apprearance and illustrating the changing phenotype. Note the facial wrinkling, proptosis, hypertelorism, wide nasal bridge, prominent nose, short columella, deep philtrum, wide mouth, everted lower lip vermilion, and microretrognathia. The ears are large, low-set, malformed, and posteriorly rotated. The fingers are long with mild camptodactyly. Long toes with broad halluces, sandal gap. Note the overall wrinkled loose skin with decrease of subcutaneous fat. Some of the facial features such as apparent hypertelorism, broad nasal root, prominent nose with wide nares and mouth, microretrognathia are already recognizable on prenatal 3D ultrasound scans auditory canals was observed and he failed the otoacoustic emissions screening. He had a low posterior hair line and a short neck. Nipples were hypoplastic and wide-spaced. The fingers were long, the thumbs adducted. Mild camptodactyly and neonatally prominent fingertip pads were noticed. His toes were long, halluces were broad with a sandal gap. He had generalized hirsutism. The overall wrinkled and redundant skin with reduced subcutaneous adipose tissue resulted in a prematurely aged appearance (see Figure 1). The echocardiography revealed an atrial septal aneurysm, a persistent foramen ovale, and a bicuspid aortic valve. The chest X-ray demonstrated cardiomegaly and scoliosis (see Figure 2). The eye examination showed persistent pupillary membranes, an enlarged and oval-shaped optic disc anomaly and peripheral retinal hyperpigmentation in both eyes. An ultrasound of the hip and the groin confirmed congenital bilateral hip dislocation and unilateral acetabular dysplasia. The abdominal ultrasound was normal. His clinical course was complicated by failure to thrive, frequent desaturations, and hypoglycemia, requiring support with tube feeding, high flow therapy and supplemental nutrition. A diagnosis of Donohue syndrome was considered but insulin levels were normal.
After he spent approximately 4 weeks in NICU, tube feeding and monitoring of his oxygen saturation were continued at home. At 6 weeks of age he presented again to the pediatric emergency care with an upper respiratory infection. His weight was 3.05 kg (À2SD).
He was discharged from the hospital the same day. At the 9-weeks follow-up, his weight was 3.66 kg (À3SD) and his head circumference was 36 cm (À4SD). No further hypoglycemia was noted. Elective hospital admission for percutaneous endoscopic gastrostomy was conducted at the age of 15 weeks. The Cormnack Lehane score III predicted a difficult airway management due to a bulging mass in the epipharynx and fiberoptic intubation was performed. After the intervention he suffered from apneic episodes which lead to an urgent transfer to the NICU. In the following days he suffered from a number of serious complications, including pneumothorax, and several infections (i.e., pneumonia, urinary tract infection, and gastroenteritis).
In addition, he developed epileptic seizures, the EEG showed pathologic monomorphic patterns with absence of epileptiform activity.
Brain imaging by magnetic resonance imaging (MRI) was performed and revealed enlarged ventricles, a slender corpus callosum, a small pituitary gland, and white matter reduction. The MRI confirmed further the previously noticed craniofacial traits of the viscerocranium, that is, hypertelorism, retrognathia, and deviated nasal septum. In addition, the MRI revealed an adipose tissue mass (DD: teratoma) compressing the epipharynx (see Figure 2). Unfortunately, no histological analysis of this tissue mass was undertaken. The boy underwent extubation after 10 days at the NICU and needed further assisted respiratory ventilation (CPAP-therapy) for additional 10 days. Due to the complications and the intermittent desaturations, he was hospitalized for almost 5 weeks. The following weeks his general condition fortunately ameliorated; he started to interact with his environment and was able to fixate objects or persons. The severe truncal hypotonia improved under physiotherapy and craniosacral therapy. Surprisingly he showed a remarkable change in the phenotype. He appeared less aged and the facial wrinkling was less prominent, but no Holter or telemetry-monitoring was done. His weight, length and head circumference remained, however, below the third centile at 4 months of age. Following the molecular diagnosis of Ogden syndrome, a standard electrocardiogram was performed at the ages of 2 weeks and 4 months which revealed no abnormalities. At 6 months of age he was hospitalized a third time with respiratory distress, severe coughing, and vomiting. His general condition was slightly reduced, F I G U R E 2 (a) Magnetic resonance imaging of the brain revealed intracranially wide inner and outer cerebrospinal fluid spaces and a very narrow corpus callosum. Note the increased fatty tissue in the epipharynx (grey arrow). (b) X-ray of the chest showing cardiomegaly, scoliosis and paravertebral left residual consolidation with positive air bronchogram but he did not appear to be very sick. Initially the respiratory condition could be stabilized, however an increasing agitation and irritability made the respiratory support difficult. Overnight his condition deteriorated rapidly. He was unable to maintain adequate ventilation and displayed agonal respiration and severe desaturations (O2 level: 45%).
A high flow ventilation was initiated, and the sedation was augmented by a subcutaneous morphine pump. Because he did not respond to morphine, midazolam was administered. He became more and more agitated and did not tolerate the ventilation. Moreover, he developed two generalized tonic seizures. He developed increased respiratory distress resulting in respiratory acidosis and respiratory failure. Chest X-rays revealed cardiomegaly, scoliosis, and paravertebral residual consolidation with positive air bronchogram on the left side (see Figure 2), but neither high-resolution lung CT-imaging nor lung biopsy was performed. As his condition progressively worsened, his parents chose to stop all life sustaining procedures. He died at the age of 7 months, probably due to complications of an obstructive bronchitis, but no autopsy was undertaken. 13:537-540) showed a random X-inactivation (48:52) in the blood probe of the maternal grandmother, who is not a carrier.

| DISCUSSION
Our observation confirms the initial reports of Ogden syndrome as an X-linked recessive early lethal condition in boys caused by the NAA10 variant Ser37Pro (Rope et al., 2011). Because the two previously described families shared a surrounding haplotype of not more than 1.5 cM, a founder variant was likely dismissed but could not be excluded (Rope et al., 2011). Since the variant occurred de novo in the boy's mother reported here, we can now unambiguously prove this variant to be recurrent. While carrier women of this variant are healthy with skewed X-inactivation, the phenotype of affected boys is consistently severe (see Table 1) Rope et al., 2011). The prematurely aged appearance with facial wrinkling, reduced subcutaneous adipose tissue and redundant skin is pathognomonic for this syndrome (Rope et al., 2011). All affected boys present the same facial anomalies such as prominent eyes, hypertelorism, downslanting palpebral fissures, broad philtrum, wide mouth and microretrognathia, as well as large, low-set ears with F I G U R E 3 Partial electropherograms after Sanger sequencing of PCR amplifications of exon 2 of NAA10 in our patient, his mother, and grandmother T A B L E 1 Clinical features of Ogden syndrome caused by the NAA10 Ser37Pro variant  (Rope et al., 2011). Our patient died at the age of 7 months, which confirms again the so far described lethal course of this syndrome. In our patient no cardiac arrhythmia was detected, but only two standard electrocardiograms were performed, which is not sufficient to exclude e.g. long QT-syndrome.
Premortal chest X-rays revealed cardiomegaly and signs of obstructive bronchitis (see Figure 2), but since autopsy was denied the underlying cause of the respiratory failure was not fully understood.
Clinical findings that were only present in our patient were the bilateral hip dislocation with an unilateral acetabular dysplasia, the ophthalmological anomalies and the adipose tissue mass (DD: teratoma) in the epipharynx.
Ogden syndrome was the first genetic syndrome linked to variant in a NAT (Rope et al., 2011). The NAA10 gene is located on the X-  Myklebust et al. Hum Mol Genetics, 2015, Vol 24, No 7, pages 1956-1976; please note that there is a discrepancy between the values in the figure and the text.
T A B L E 2 Phenotypes and genotypes of patients with NAA10-related syndrome    His16Pro: Impaired NatA complex formation, 4-fold reduced catalytic activity of NatA complex Tyr43Ser: Significant decrease in catalytic activity, reduced stability Ile72Thr: 75% reduction in catalytic activity toward the in vitro monomeric NAA10 substrate (no reduction in catalytic activity NatA substrate) Arg83Cys: Clear reduction ($60%) of the catalytic activity Val107Phe: Nearly abolished enzymatic activity Val111Gly: The Ser37Pro missense variant is localized in exon 2 and has been well studied in vitro and in vivo. The serine codon is highly conserved in eukaryotes and lies within the dimerization domain with Naa15 (see Table. 2) (Rope et al., 2011). The Ser37Pro variant showed decreased enzymatic activity in in vitro acetylation assays, reduced NatA-complex formation and an impaired interaction with hNaa50, suggesting the lack of N-terminal-acetylation of a small number of proteins Rope et al., 2011). Furthermore, S37P-hTERT cells have reduced cell proliferation and dysregulation regarding cell-cell contact inhibition and migration . Lee Figure 4). An excellent overview of these overlapping yet distinct disorders associated with pathogenic variants in the NAA10 gene was published by Wu and Lyon, who recommend that these diseases should be referred to more broadly as NAA10-related syndrome, given the enormous phenotypic variability (Wu & Lyon, 2018  Decreased stability, decreased monomeric catalytic activity, NatA catalytic activity remained unchanged Arg116Trp: Very mild reduction in the catalytic activity Phe128Ile: Near loss (>90%) of the catalytic activity, reduced stability Abbreviations: CVS, cardiovascular system; ID, intellectual disability; MGM, maternal germline mosaicism; NA, not available; WNT, wingless-related integration site. (Rauch et al., 2012). In vitro studies showed that this variant has a significant but rather small reduction in the catalytic activity (15%) in comparison to the Ser37Pro variant, a plausible explanation for the mild phenotype in the boy (Popp et al., 2015). However, in 2015, Casey et al. argued that the relation between Naa10 variants and disease phenotypes is more complex and that the in vitro catalytic activity in itself is not always sufficient in explaining phenotypes observed in patients (Casey et al., 2015).  .
Functional studies of this variant revealed an increased turnover rate when expressed in human cell lines, a 75% reduction in catalytic activity toward the in vitro monomeric NAA10 substrate, but surprisingly no reduction in catalytic activity when tested for the NatA substrate, leading to the assumption that this Ile72Thr is protected from degradation and destabilization by forming a functional NatA complex . In summary these functional studies of NAA10 missense variants, demonstrating a variable effect on the ability of NAA10 to acetylate substrates, are supporting the hypothesis that the level of acetylation dysfunction and affected substrates is an important underlying pathomechanism with a possible correlation toward the clinical phenotype (Johnston et al., 2019).
Compared to missense variants, alterations in the NAA10 gene which result in a (partial) loss of protein function due to reduced mRNA levels can lead to syndromic microphthalmia/anophthalmia in boys (Esmailpour et al., 2014;Johnston et al., 2019;Shishido et al., 2020). Complete loss-of-function of NAA10, however, is thought to be lethal in males (Popp et al., 2015).
F I G U R E 4 Schematic representation of the genomic structure plus the functional domains of the human NAA10 gene with representation of the genotype-phenotype correlation of the so far described NAA10 pathogenic variants in males (above NAA10 and NAA10) and in affected females index cases (below NAA10). The genomic structure is based on isoform 1, encoded by transcript NM_003491.3. The domain structure corresponds to the following Uniprot identifiers P41227 The majority of variants in male patients were maternally inherited and most of the female carriers were healthy or had only minor features (see Table 2). But as already mentioned, female index patients with pathogenic, apart from one maternal mosaic variant merely de novo missense variants in the NAA10 gene have been equally identified over the time. The phenotype in females with NAA10-related N-terminal-acetyltransferase deficiency is among others characterized by moderate to severe developmental delay and ID with no or very limited speech, postnatal growth failure, microcephaly, seizures, different skeletal, brain, and organ anomalies and cardiac arrhythmias (see Table 2) (Bader et al., 2020;Cheng et al., 2020;McTiernan et al., 2018;Popp et al., 2015;Saunier et al., 2016;Sidhu et al., 2017;Thevenon et al., 2016).
X-chromosome inactivation studies in affected females, when undertaken, were not conclusive, showing either random or skewed X-inactivation. Studies of acetylation activity revealed severely abolished activity in most but not all of these de novo variants causing a severe phenotype in females (Cheng et al., 2020;Popp et al., 2015;Saunier et al., 2016).
Ogden syndrome was the first genetic disorder which contributed highly to the research and decipherment of the fascinating role of Nterminal acetylation in development and disease. With the identification of different NAA10 alterations, we slowly gain insight into its complexity and are starting to unravel the contributing factors and mechanism underlying this broad clinical spectrum of NAA10-related disorders.

| CONCLUSION
In summary we presented the ninth case of a boy with Ogden syndrome who was diagnosed in Zurich, Switzerland more than 5000 miles away from the hometown of the original family in Utah, USA. We could confirm the consistency of the clinical phenotype and recurrence of this rare lethal X-linked recessive disorder caused by the NAA10 Ser37Pro variant. Our patient exhibited the full phenotypic spectrum of Ogden syndrome (Aksnes et al., 2016), which is a highly recognizable syndrome, in particular due to the remarkable similar facial gestalt of affected boys. We further delineated the evolving phenotype of this condition, additionally presented new clinical findings and reflected shortly on the extensive phenotypic variability that is linked to different variants in the NAA10 gene.

ACKNOWLEDGMENT
We are deeply grateful to the family for sharing their journey.