A Novel YWHAG Variant L173S Causes Developmental and Epileptic Encephalopathy by Disrupting the Hydrophobic Internal Protein Structure

ABSTRACT

Background

Developmental epileptic encephalopathy 56 (DEE56) is a monogenic DEE type caused by heterozygous mutations in YWHAG. To our knowledge, fewer than 30 cases of DEE56 have been reported globally, and our understanding of YWHAG's function remains limited.

Methods

Whole exome sequencing (WES) was performed on the patient and his parents. Structural conservation analysis of YWHAG was conducted using Consurf and PyMol. A literature search for relevant cases was performed in PubMed and Google Scholar.

Results

The patient is a 6‐year‐2‐month‐old boy who developed refractory complex seizures starting at 8 months of age. He also exhibits intellectual disability, language impairment, and poor motor coordination. WES identified the de novo occurrence of a novel heterozygous YWHAG missense variant, c.518T>C (p.L173S), in the patient. L173 resides within the hydrophobic internal core formed by three alpha helices of YWHAG, and the residues constituting this internal core are highly evolutionarily conserved. The L173S substitution introduces a hydrophilic side chain into the hydrophobic core composed of three aliphatic residues. Ten missense mutations have been reported previously. Among them, five (E15, R57, D129, R132, and Y133) are associated with the ligand‐binding region.

Conclusion

The functional domain involving the L173 residue of YWHAG remains unknown. Our findings suggest that the disruption of the stability of the highly conserved internal core of the YWHAG protein may be one mechanism leading to functional impairment, distinct from the previously proposed pathogenic models of dimer formation defects and/or impaired binding to phosphopeptide ligands. This may provide insights into the functional mechanisms of YWHAG and potential therapeutic strategies.

1. Background

Developmental epileptic encephalopathies (DEEs) are a group of severe genetic epilepsy syndromes characterized by early‐onset refractory seizures and developmental impairment or regression. DEEs encompass two sets of syndromes: developmental encephalopathies (DEs) and epileptic encephalopathies (EEs), where the severe childhood epilepsy itself can cause developmental impairment, underscoring the importance of understanding the mechanisms of seizure occurrence and clinical management in DEEs (Bartolini 2021). Improving seizure control may help ameliorate the disease course and prognosis (Scheffer et al. 2017), thus elucidating the etiologies and developing targeted therapies could be a major direction for improving outcomes in DEEs. By this definition, 118 monogenic DEE subtypes (https://omim.org/phenotypicSeries/PS308350) have been identified to date.

DEE56 (MIM #617665) is attributed to heterozygous mutations in the YWHAG gene. YWHAG, also known as 14‐3‐3γ, plays a crucial regulatory role in mitosis and cell proliferation signaling pathways. Unlike many epilepsy‐associated transmembrane ion channel proteins, YWHAG is a cytosolic regulator involved in the modulation of pathways such as PKC and RAF1, acting as an important transcriptional regulator (Autieri and Carbone 1999; Morrison 1994). Guella et al. (2017) identified a YWHAG missense mutation in three DEE56 cases, located within the positively charged binding groove that interacts with phosphopeptides, providing insights into the potential mechanism of YWHAG functional impairment. However, the structure–function relationship of YWHAG remains unclear.

2. Methods

This study was explained to the patient's parents, and informed consent was obtained. The relevant procedures and content were approved by the Medical Ethics Committee of Dalian Women and Children's Medical Center (Group), document number: DLET‐KY‐2023‐75.

The proband's clinical manifestations, including clinical phenotype, developmental assessment, laboratory investigations, brain MRI, and electroencephalography, were collected.

Whole exome sequencing (WES) and copy number variation (CNV) sequencing of the quartet family were carried out by Chigene Ltd. (Beijing, China), and candidate variants were validated by Sanger sequencing. WES was performed using the xGen Exome Research Panel v2.0 (IDT, USA) for exome capture library construction. High‐throughput sequencing was conducted on the NovaSeq6000 system (Illumina, USA). Sequencing procedures, data generation, cleaning, and quality control followed the manufacturer's recommended standard protocols. The average sequencing depth was 100X, with exome sequence coverage ≥ 99%. WES data were analyzed through Chigene's precision genetic diagnosis cloud platform (https://www.chigene.cn/zaixianfenxipingtai/) for automated bioinformatics analysis, generating insertions/deletions (indels) ≤ 50 bp and point mutations. Chigene's proprietary algorithms were used to detect CNVs spanning multiple consecutive exons. CNV detection was also performed on the NovaSeq6000 platform, as previously reported (Xie and Tammi 2009). Through Chigene's integrated variant database, including dbSNP, ClinVar, HGMD pro, gnomAD, and OMIM, all identified variants were annotated for minor allele frequency (MAF), reported pathogenicity cases, literature, and associated diseases. Variant pathogenicity was classified according to the American College of Medical Genetics (ACMG) guidelines for clinical practice. The reference transcript for YWHAG was NM_012479.4.

Structural conservation analysis of the YWHAG protein model (PDB: 3UZD) was performed using The ConSurf Server (https://consurf.tau.ac.il), and visualization was done with PyMol Version 2.5.8. In addition to the YWHAG variant identified in this study, previously reported mutation sites E15, R57, D129, R132, and Y133 were also analyzed for structural conservation.

A literature search was conducted in PubMed and Google Scholar using the keywords “YWHAG,” “14–3‐3γ,” or “14‐3‐3gamma” until July 2024 to collect and summarize reported patient phenotypes and YWHAG variant data.

3. Results

The patient is a 6‐year‐2‐month‐old boy born to non‐consanguineous parents with a healthy older brother. He was delivered at 36 weeks of gestation via normal vaginal delivery with an unremarkable perinatal history. At 8 months old, he experienced his first febrile seizure, which was simple in nature. At 16 months, he had another episode of complex febrile seizure. At 3 years and 1 month, he started having afebrile seizures while awake, presenting with loss of consciousness, eye fixation, blinking, slight pallor, mild tremors in the lower limbs, lasting approximately 1 min and resolving with postictal drowsiness. Despite the introduction of sodium valproate at 2.5 months, seizures persisted. Lacosamide was added, and the patient remained seizure‐free for 5 months. However, seizures recurred, manifesting as loss of consciousness, unresponsiveness to calls, eye fixation, blinking, slight pallor, and flaccid limbs, lasting approximately 20 min and resolving with eye closure and slight irritability. The addition of oxcarbazepine resulted in a 6‐month seizure‐free period. At 5 years and 3 months, a new seizure type emerged, characterized by brief (2–3 s) eye fixation and nystagmus while awake, self‐resolving. Lacosamide was gradually discontinued, and lamotrigine was introduced. The patient remained seizure‐free for 7 months until a febrile illness triggered a generalized tonic–clonic seizure lasting approximately 1 min, shorter than previous episodes. Current anticonvulsant therapy includes lamotrigine 50 mg q12h (3.4 mg/kg/day), sodium valproate 8 mL q12h (22.0 mg/kg/day), and oxcarbazepine 7 mL q12h (28.9 mg/kg/day).

The patient achieved head control at 3 months, sitting at 6 months, walking at 14 months, and speech at 20 months. He had a history of frequent falls due to poor coordination. After rehabilitation training, his gait is now normal, but fine motor skills lag behind peers. Currently, he can answer questions and speak in sentences, but cannot comprehend complex instructions. His expressive language is impaired, with a slow speech rate and mild deficits in calculation and memory. Developmental assessment (Wechsler Intelligence Scale for Children‐Revised, WISC‐R) at 6 years and 2 months: Verbal IQ 52 (Information 3%, Similarities 5%, Arithmetic 1%, Comprehension 3%, Digit Span 3%), Performance IQ 60 (Picture Completion 6%, Coding 1%, Picture Arrangement 4%, Block Design 8%, Object Assembly 7%), Full‐Scale IQ 48. Social adaptation is normal.

Brain MRI revealed mild dilatation of the right temporal horn of the lateral ventricle and widening of the right temporal subdural space (Figure 1A).

FIGURE 1.

Brain MRI and electroencephalography findings in the DEE56 patient. (A) Mild intracranial abnormalities, including mild dilatation of the right temporal horn of the lateral ventricle and widening of the right temporal subdural space. (B) Electroencephalography characteristics of the patient during sleep (upper) and wakefulness (lower).

Long‐term video‐electroencephalography showed an abnormal childhood electroencephalogram with bifrontal and bitemporal intermittent slow waves across wakefulness and sleep, as well as one episode of left frontal rhythmic slow wave discharge. Generalized spike‐and‐slow‐wave discharges, slow wave bursts, sometimes localized to the frontal region, and frontal intermittent sharp slow waves were observed during wakefulness (at 5 years and 3 months). The most recent video‐electroencephalogram (at 6 years and 2 months) demonstrated background slowing compared to age‐matched controls, with generalized 2–3 Hz spike‐and‐slow‐wave/sharp‐and‐slow‐wave discharges during wakefulness and sleep, more prominent in the frontal regions (Figure 1B).

WES identified the de novo occurrence of a novel heterozygous YWHAG missense variant c.518T>C (p.L173S) in the patient, which was validated by Sanger sequencing (Figure 2). This variant is classified as likely pathogenic (PS2_Moderate+PM2+PP2+PP3) and has not been recorded or reported in public databases. Structural conservation analysis of the YWHAG protein revealed that L173 resides within Helix 8 (AA 169‐186) of the internal core formed by three alpha helices (Helix 8, 9 (AA189‐207), and 11 (215‐234); Xu et al. 2012), and the amino acid residues in close proximity within these helices are highly conserved (Figure 3A). Including L173, the three spatially adjacent residues form a hydrophobic core composed of aliphatic amino acids (the other two being A204 on Helix 9 and I222 on Helix 11, Figure 3B), while the L173S mutation introduces a hydrophilic side chain into this hydrophobic core (Figure 3C). Additionally, we analyzed the five previously reported missense mutation sites, E15, R57, D129, R132, and Y133, which are spatially proximal, highly conserved residues constituting a loose, hydrophilic structure favorable for the binding of polar ligand groups (Figure 3D).

FIGURE 2.

Sanger sequencing validation of the NM_012479.4 (YWHAG) c.518T>C variant in the patient and three family members.

FIGURE 3.

Conservation and structural analysis of the YWHAG protein. (A) Three helical structures, Helix 8, 9, and 11, with highly conserved amino acid residues in close spatial proximity, forming the internal core of the protein. (B) L173 resides on Helix 8, and together with the spatially adjacent, highly conserved A204 (Helix 9) and I222 (Helix 11), these three aliphatic amino acids form a hydrophobic internal core. (C) Upon S173 mutation, the mutant serine introduces a hydrophilic side chain into this hydrophobic core region. (D) The five previously reported highly conserved missense mutation sites all carry hydrophilic side chains, forming a loose structure favoring ligand (shown in gray wireframe) binding through their polar groups. The color key for conservation is shown in the upper right corner.

To date, 15 variants have been reported in 26 DEE56 cases, including 11 missense mutations (including the present study) (Table 1).

TABLE 1.

Characterization of phenotypes and YWHAG variants in previously reported cases and the present study (Guella et al. 2017; Xie and Tammi 2009; Kim et al. 2021; Iodice et al. 2022; De Rubeis et al. 2014).

Case	Present study	1 (Guella et al. 2017)	2 (Guella et al. 2017)	3 (Guella et al. 2017)	4 (Guella et al. 2017)	5 (Xie and Tammi 2009)	6 (Xie and Tammi 2009)	7 (Xie and Tammi 2009)	8 (Xie and Tammi 2009)	9 (Xie and Tammi 2009)	10 (Xie and Tammi 2009)	11 (Xie and Tammi 2009)	12 (Kim et al. 2021)	13 (Iodice et al. 2022)	14 (De Rubeis et al. 2014)	15 (De Rubeis et al. 2014)
YWHAG variants	c.518T>C (p.L173S)	c.394C>T (p.R132C)	c.44A>C (p.E15A)	c.394C>T (p.R132C)	c.394C>T (p.R132C)	c.169C>G (p.R57G)	c.398A>C (p.Y133S)	c.532A>G (p.N178D)	c.394C>T (p.R132C)	c.394C>T (p.R132C)	c.169C>T (p.R57C)	c.529C>A (p.L177I)	c.619G>A (p.E207K)	c.170G>A (p.R57H)	c.170G>A (p.R57H)	c.170G>A (p.R57H)
Type of inheritance	De novo	De novo	De novo	De novo	De novo	De novo	De novo	De novo	De novo	De novo	De novo	De novo	De novo	De novo	Maternal	De novo
Sex	Male	Female	Female	Female	Female	Female	Male	Male	Female	Male	Female	Female	Male	Male	Male	Female
Age	6 y.o.	18 y.o.	10 y.o.	22 y.o.	15 y.o.	15 y.o.	16 y.o.	10 y.o.	23 y.o.	4 y.o.	10 y.o.	7.5 y.o.	4 y.o.9 m.o.	8 y.o.	3 y.o.10 m.o.	34 y.o.
Age at epilepsy onset	8 m.o.	12 m.o.	6 m.o.	< 6 m.o.	< 6 y.o.	10 m.o.	16 y.o.	2 y.o.	< 6 m.o.	2 y.o.	< 5 y.o.	n.m.	9 m.o.	1 y.o. 6 m.o.	1 y.o.11 m.o.	2 y.o.
Character of epilepsy	1. Febrile convulsions focal seizures with 1 persistent state: staring eyes with blinking, slightly pale face, and slight shaking of both lower limbs. Generalized tonic‐clonic seizures. Atypical absences: staring eyes with nystagmus	1. Generalized myoclonus, 2. Atypical absence, 3. Generalized tonic‐clonic	Prolonged seizures with fever, followed by two episodes of status epilepticus, with developmental regression and hemiparesis	1. Myoclonus, 2.Long‐term generalized tonic‐clonic spasm with fever, 3.Generalized myoclonus, 4. Atonia, 5. Generalized tonic‐clonic spasm	1 Absence seizure, 2 eyelid myoclonus, 3 myoclonus, 4 continuous absence seizure	1. Atonia, 2. Focal, 3. Generalized tonic‐clonic	Isolated generalized tonic‐clonic	Atonic	1 Generalized tonic‐clonic, 2 Generalized myoclonus, 3 Atonia	Generalized tonic‐clonic	Frontal lobe epilepsy	Atonic	Myoclonus with extension of both hands, no clustering of jerks, focal seizures	1. Absence, febrile and afebrile generalized tonic‐clonic convulsions	Generalized tonic‐clonic	Generalized tonic‐clonic
Neurodevelopmental delay	IQ 60	Mild to moderate	IQ 55	Moderate to severe	WPPSI III (6 years), VIQ 73, PIQ 58	Mild to moderate	Mild to moderate	Moderate	Moderate	Mild	Moderate	Mild to moderate	Normal	Mild	Moderate	Mild to moderate
Language development	Delayed	Early onset language developmental delay	Delayed	Delayed	Mildly delayed	Normal	Normal	language developmental delay, repeated language	language developmental delay	Mildly delayed	Needs training, can only speak short sentences	Delayed	Normal	Delayed	Delayed	Delayed
Age at walk	14 m.o.	n.m.	n.m.	n.m.	n.m.	15 m.o.	23 m.o.	24–30 m.o.	16 m.o.	21 m.o.	22 m.o.	18 m.o.	17 m.o.	15 m.o.	18 m.o.	n.m.
Deformity	—	Wide‐set eyes, lower palpebral fissure, small ears	Null	Null	Null	Downward‐pointing palpebral fissures, upturned nose, no cupid's bow, small ears, prominent forehead	Ptosis, downward palpebral fissures, downward corners of the mouth	Upturned nose, thickened nose wings, wide mouth	Null		Upward slanting palpebral fissure, short nose bridge, wide mouth	Bulbous nose, thin upper lip, wide‐set eyes, and prominent forehead	Null	Null	Null	Null
Others	—	Hyperactivity	—	—	—	ASD	—	ASD	ASD	—	—	—	—	Hyperactivity	—	—
EEG	As mentioned in the article	Ictal period: myoclonic convulsions, generalized spike‐wave discharges Interictal period: 2 y.o.: background rhythm disorder, generalized atypical spikes, frequent spikes in both frontal lobes; 14 y.o.: background rhythm disorder, rare sharp waves in bilateral frontal lobe	n.m.	Ictal period: spikes and slow waves, polyspikes and slow waves Interictal period: 21 m.o.: generalized 3 Hz spikes with absence seizures	Illness period: None. Interictal period: 8 y.o.: Bilateral frontotemporal spikes, generalized spikes	—	—	Interictal: Prolonged widespread 2.5 Hz spike‐wave activity	Interictal: generalized polyspike and slow wave discharges	—	—	Normal between seizures	Ictal period: 9 m.o.: Generalized spikes mainly in the bilateral frontal lobes, Interictal period, 9 m.o.: Generalized non‐attenuated spike discharges, spikes with no high‐dysrhythmia pattern, peak arrhythmia in the whole body, 3 y.o. 10 m.o.: (9 m.o.) Spikes in the right posterior frontal area, independent spikes in the left posterior frontal area	Interictal: Background slowing or mild abnormalities. Only some EEG recordings show generalized or bifrontal spikes and SW complexes	Normal between seizures	Normal between seizures
				10 y.o.: generalized polyspikes with myoclonic seizures; 14 y.o.: sporadic spikes
Brain MRI	Slightly larger temporal angle of the right ventricle and the subarachnoid space	3 y.o.: Asymmetric brainstem considered unimportant	Generalized atrophy with diffuse white matter loss	10 y.o.: normal	Normal	Normal	Normal	Normal	Normal	额叶的高信号病灶	Subtle signal abnormalities in the subcortical white matter of the frontal lobe	Normal	Nonspecific FLAIR sequence high signal	Normal	Normal	—
Anti‐epilepsy treatment	Valproic acid Perampanel, Oxcarbazepine, Lamotrigine	Clonazepam, Lamotrigine, Sodium valproate, Ethosuximide	Valproic acid	Valproic acid, Stiripentol	Sodium valproate, Lamotrigine	Levetiracetam, Ethosuximide	Not treated	Ethosuximide	Stiripentol, Sodium valproate	Valproic acid	Sodium valproate, Carbamazepine	Not treated	Valproic acid, Levetiracetam	Valproic acid	Sodium valproate	Phenytoin sodium, Carbamazepine, Sodium valproate
Drug resistance	Partially effective	Null	Null	Partially effective	null	Null	Null	No response to lamotrigine	Partially effective	Null	Null	—	Valproic acid partial response, Levetiracetam no seizures	Null	Null	Partially effective

Case	16 (Kim et al. 2021)	17 (Iodice et al. 2022)	18 (Iodice et al. 2022)	19 (Iodice et al. 2022)	20 (Iodice et al. 2022)	21 (Iodice et al. 2022)	22 (Iodice et al. 2022)	23 (Iodice et al. 2022)	24 (Iodice et al. 2022)
YWHAG variants	c.373A>G (p.L125G)	c.304del (p. Sr102 Afs*7 )	c.124C>T (p.Arg42Ter)	c.124C>T (p.Arg42Ter)	c.124C>T (p.Arg42Ter)	c.124C>T (p.Arg42Ter)	c.124C>T (p.Arg42Ter)	c.124C>T (p.Arg42Ter)	c.373A>G (p.Lys125Glu)
Type of inheritance	De novo	n.m.	Maternal	Maternal	Maternal	Maternal	Maternal	Maternal	De novo
Sex	Male	Female	Male	Female	Male	Female	Male	Female	Male
Age	3 y.o.	5 y.o.	40 y.o.	38 y.o.	14 y.o.	3 y.o.	4 y.o.	8 y.o.	3 y.o.
Age at epilepsy onset	19 m.o.	24 m.o.	< 1 y.o. to4 y.o.1–2per year	< 1 y.o. to4 y.o.1–2per year	2 y.o. to5 y.o.1–2per year	7 m.o.	8 m.o.5 per year	2 y.o.–3 y.o.1–2 per year	19 m.o.
Character of epilepsy	Febrile seizures, Myoclonus	Myoclonus	Febrile seizures, Generalized tonic‐clonic	Febrile seizures, Generalized tonic‐clonic	Febrile seizures, Generalized tonic‐clonic	Febrile seizures, Generalized tonic‐clonic, Myoclonus	Febrile seizures, Generalized tonic‐clonic	Febrile seizures	Febrile seizures, Generalized tonic‐clonic，Myoclonus seizures
Neurodevelopmental delay	DD	Normal	Normal	Normal	Normal	n.m.	n.m.	n.m.	n.m.
Language development	DD	DD	Normal	Normal	Normal	n.m.	n.m.	n.m.	n.m.
Age at walk	n.m.	n.m.	n.m.	n.m.	n.m.	n.m.	n.m.	n.m.	n.m.
Deformity	Prominent forehead, spaced teeth	Null	n.m.	n.m.	n.m.	n.m.	n.m.	n.m.	n.m.
Others	—	—	—	—	—		—	—	—
EEG	Generalized spike‐wave interictal	Myoclonus, generalized spike and slow wave discharge	Normal	Normal	Normal	Myoclonus epileptic seizures with generalized irregular multispike‐wave	Normal	n.m.	Generalized spike‐wave
Brain MRI	Normal	Normal	—	—	Normal	Normal	Normal	n.m.	Normal
Anti‐epilepsy treatment	Sodium valproate	Sodium valproate				Sodium valproate	Sodium valproate	—	Sodium valproate
Drug resistance	Null	Null				Null	Null	—	Null

Abbreviations: ASD, autism spectrum disorder; DD, developmental delay; m.o., months old; n.m., not mentioned; y.o., years old.

4. Discussion

DEEs encompass a spectrum of clinical phenotypes overlapping with other developmental disorders, including psychomotor developmental delay, intellectual disability, impaired or absent speech development, behavioral abnormalities, hypotonia, movement disorders, seizures, microcephaly, and dysmorphic facial features (Guerrini et al. 2023). Therefore, diagnosis based solely on clinical phenotypes is challenging, with the primary diagnostic focus being on the early onset of epilepsy, typically in infancy, and the varying types and severity of seizures. Before the identification of the YWHAG‐related DEE type (MIM:#194050), YWHAG was implicated in the rare phenotype of epilepsy and severe psychomotor developmental delay associated with Williams–Beuren syndrome or the 7q11.23 deletion syndrome (Morimoto et al. 2003). Subsequent discoveries of single‐gene DEE56 cases exhibited more consistent DEE phenotypic features (Guella et al. 2017), aligning with the patient's presentation in this study.

YWHAG, also known as 14‐3‐3γ, is highly expressed in the mammalian brain, and its primary known function is binding to target proteins, thereby altering their activity, modification, and intracellular localization (Bridges and Moorhead 2004; Jin et al. 2004; Obsilova et al. 2008; Lundby et al. 2012). This was demonstrated in the study published by Guella et al. (2017). Through the investigation of the YWHAG R132C and E15A variants, the authors proposed that the pathogenic mechanism of YWHAG variants involves disrupting dimerization and/or phosphopeptide ligand binding (Guella et al. 2017), which our analysis corroborates (Figure 3D). Furthermore, we found that the five previously reported missense mutation sites, E15, R57, D129, R132, and Y133, collectively form a loose, hydrophilic surface structure for phosphopeptide ligand binding, consistent with Guella et al.'s (2017) speculation but differing from our findings. YWHAG L173, together with the spatially adjacent A204 and I222, forms a hydrophobic internal core of three aliphatic residues (Figure 3A). In fact, this combination favors the stability of the internal alpha‐helical regions, suggesting that the entire alpha‐helical structure containing L173 is relatively more evolutionarily conserved, further contributing to the stability of the internal helical structure. The L173S mutation introduces a hydrophilic side chain, and L173 is located at the end of the three alpha‐helical regions. Therefore, we hypothesize that L173S not only disrupts the stability of the three alpha‐helical regions, creating a more relaxed structure at the terminus or protein surface, but may also lead to abnormal ligand binding due to the introduction of the hydrophilic side chain. However, the function of this region remains unclear, precluding more reasonable speculation. Nevertheless, the distinct findings associated with the L173S mutation may suggest a different pathogenic mechanism from the known variants E15, R57, D129, R132, and Y133.

The current proposed primary pathogenic mode for YWHAG missense mutations is the formation of abnormal dimers composed of wild‐type YWHAG monomers and mutant monomers with impaired target protein binding, resulting in a dominant‐negative effect where the YWHAG mutants disrupt the function of the wild‐type monomers. In this model, the severity of the patient's phenotype may primarily depend on the degree of disruption in ligand binding caused by the mutation (Jin et al. 2004). Exceptions to this model are truncating mutations or heterozygous deletions that cannot form dimers, explaining the milder phenotypes observed in these cases, such as the association of the R42* variant with milder febrile seizures and childhood myoclonic epilepsy (Ye et al. 2021). Aside from this, no other genotype–phenotype correlations specific to DEE56 have been established due to the phenotypic heterogeneity of DEEs.

5. Conclusion

We identified a novel YWHAG L173S variant in a typical DEE patient, expanding the mutational spectrum of DEE56. Based on the location and structural conservation features of L173, we found that this variant cannot be explained by the currently known pathogenic models for YWHAG missense mutations. We propose that a structure‐based pathogenic mode, represented by L173S, may provide new insights for elucidating the YWHAG function and designing therapeutic targets.

Author Contributions

Yuan Jin and Zhe Tao: conceptualization. Yuan Jin: writing – original draft. Yuan Jin: interpretation of data. Yuan Jin: writing – review. Yuan Jin, Zhe Tao, and Mei Ling Luo: validation. Yuan Jin: revision of the draft. Zhe Tao: writing – review and editing. Qian Niu, Shan Na Liang, Mei Ling Luo, and Xiao Lin Su: analysis of data. Qian Niu: formal analysis. Shan Na Liang: investigation. Mei Ling Luo and Xiao Lin Su: acquisition. All authors have carefully reviewed and consented to the final published version of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.