AMPA receptor GluA2 subunit defects are a cause of neurodevelopmental disorders

AMPA receptors (AMPARs) are tetrameric ligand-gated channels made up of combinations of GluA1-4 subunits encoded by GRIA1-4 genes. GluA2 has an especially important role because, following post-transcriptional editing at the Q607 site, it renders heteromultimeric AMPARs Ca2+-impermeable, with a linear relationship between current and trans-membrane voltage. Here, we report heterozygous de novo GRIA2 mutations in 28 unrelated patients with intellectual disability (ID) and neurodevelopmental abnormalities including autism spectrum disorder (ASD), Rett syndrome-like features, and seizures or developmental epileptic encephalopathy (DEE). In functional expression studies, mutations lead to a decrease in agonist-evoked current mediated by mutant subunits compared to wild-type channels. When GluA2 subunits are co-expressed with GluA1, most GRIA2 mutations cause a decreased current amplitude and some also affect voltage rectification. Our results show that de-novo variants in GRIA2 can cause neurodevelopmental disorders, complementing evidence that other genetic causes of ID, ASD and DEE also disrupt glutamatergic synaptic transmission.

are intelligible. There is no evidence of developmental regression (Supplementary Table 6). She carries a diagnosis of intellectual disability (IQ of 40 to 50, although this may be an underestimate given she has substantially better receptive than expressive language function). She has an autism spectrum disorder (ASD) with some atypical features, attention deficit hyperactivity disorder (ADHD) and dyspraxia. She also exhibited behavioural abnormalities from early infancy. As an infant, she was very irritable and would cry often. She also had poor eye contact. She exhibited head banging and self-injurious behaviours as a child. She continues to exhibit episodic aggression toward others, albeit infrequently. She also has tactile sensitivity around her face and mouth (does not like people brushing her teeth). A distinct feature of her current mental status and behaviour is that, although she is highly perseverative, she sustains remarkably good eye contact, and is friendly, especially with new people, and exhibits an unusually high level of "eagerness" bordering on overt psychomotor agitation whenever she successfully shares an idea or interest (vigorously nodding, smiling, repeating, tensing her entire body, and displaying intense affective arousal). There is no history of seizures. Physical examination at the age of 29 years revealed a small body size (height ~25 th centile and weight ~3 rd centile), and microcephaly (OFC 52.5 cm, <3 rd centile). She had normal brain imaging. She had a normal array-comparative genome hybridization (CGH) and unremarkable metabolic work-up. WES revealed a de novo missense variant in GRIA2 (NM000826.3: c.2700G>T; p.Gly792Val). A de-novo variant of uncertain significance was also identified in this Patient by trio WES (NM_001127235: c.212dupA; p.Asn71Lysfs*29) in the GPBP1 gene (MIM #608412).

Supplementary Note 7
Patient 7 is an 11-year-old Latino-American girl who started with daily clusters of infantile spasms since the age of 15 months. Additional seizure types included atypical absences and nocturnal episodes characterized by upper limb stiffening in extension and breathing changes. EEG showed diffuse polyspike and slow spike and wave at 2.5 C/Sec. She has received multiple AEDs including clonazepam clobazam, felbamate, rufinamide, levetiracetam, valproic acid, lamotrigine and perampanel, but clinical response was poor, and ketogenic diet also failed to bring about an improvement (Supplementary Table 5). She also showed global developmental delay with severe ID, abnormal behavior with RTT-like features (including head nodding, rocking and breathing with frequent hyperventilation episodes, Supplementary Table 6 and Supplementary Video 5). At the age of 10 years her height was 134 cm (25 th -50 th centile) and weight 26 kg (10 th centile). She never acquired the ability to walk. RTT was considered and she was negative for MeCP2 variants. Large epilepsy multigene panels failed to identify a mutation. Trio WES identified a de novo missense variant in GRIA2 affecting the Q/R RNA editing site (NM000826.3: c.1819C>G; p.Gln607Glu/p.Arg607Gly). Sequencing data were reviewed for evidence of mosaicism in both the Proband and parent samples as the de-novo variant affecting the Q/R site was present only in 14% of exome sequencing reads and present at an allele ratio of < 35% in the Proband using both NGS and ABI data. WES also identified the de novo variant of uncertain significance (NM_003870: c.4186A>G; p. I1396V) in the gene IQGAP1 (MIM #603379).

Supplementary Note 8
Patient 8 is a 2-year-old boy of mixed Caucasian and Latino American ancestry. He was born preterm (at 30 weeks of gestation). He has an history of delay of his developmental milestones. WES revealed a de novo variant in GRIA2 (NM000826.3: c.88+2T>C; p.?) variant which is likely to affect splicing of exon 1. This variant is predicted by three in silico tools (MaxEnt, NNSPLICE, HSF) to result in an abolishment of the natural donor side and strengthening of an alternative donor splice site at position c.88+4 ( Supplementary Fig. 4).

Supplementary Note 9
This is a 9-year-old boy born at term after an uneventful pregnancy. At birth, his length 47 cm and OFC of 33.5 cm (10 th centile). He has a history of developmental delay, ID and ASD. He presents joint hyper-mobility. He never had a documented seizure, and his EEG and his brain imaging studies were normal. WES revealed a de novo missense variant in GRIA2 (NM000826.3: c.1582C>A; Pro528Thr).

Supplementary Note 10
This is a 5-year-old Chinese girl with ID and ASD. At her current age height is 111cm, weight is 19kg and OFC is 49.5cm (25 th -50 th centile). The first abnormalities were noted in infancy with impaired social interaction and abnormal behavior. The patient was diagnosed with severe ID (PPTV at 4.5 years: 57). There is also a history of ritualistic behavior and unusual preoccupations such as focusing at line objects and neon lamp. At her current age she presents speech delay (first words at the age of 16 months) and cannot complete intelligible sentences. She has never had seizures. She has autistic features and obsessive-compulsive thoughts and behaviors. Targeted Capture and High-Throughput Sequencing Using Molecular Inversion Probes (MIPs) identified a de novo frameshift deletion in GRIA2 (NM000826.3:c.1785del; p.Phe595LeufsX37), predicted to introduce a premature truncation in the resulting GluA2 protein.

Supplementary Note 11
Patient 11 is an 8-year-old Chinese Han boy affected with severe ID and ASD. At birth, his growth parameters were reported within normal ranges (25 th -50 th ). At the current age of 8 years OFC is 48.5 cm (10 th centile). The first abnormalities were seen at 17 months of age with impairment of communication and social interaction. The patient was diagnosed with severe ID (Gesell at 3 years: adaptive: 58, gross motor: 83, find motor: 60, language: 58, personal-social behavior: 66). There was also a history of speech delay with the first words pronounced at the age of 19 months. At his current age he still cannot complete phrases. Brain imaging was unremarkable. Seizures have not been noted. The behavior is characterized by hyperactivity and autistic features, including ritualistic behaviors. In this Patient, targeted sequencing with MIPs identified a de novo , a GRIA2 de-novo variant (NM000826.3:c.1844+1G>A; p.?) which is predicted to cause a complete loss of donor splice site of exon 11 according to all tools for which predictions were available ( Supplementary Fig. 5).

Supplementary Note 12
Patient 12 is a 6-year-old boy with a history of mild developmental delay, ID and ASD. At his current age of 6 years his height is 110 cm, weight is 20kg and OFC is 50 cm (25 th -50 th centile). The first abnormalities were noticed during late infancy around the age of 2 years, when a delay in speech and cognition were noted. At the age of 3.4 years ID was documented (Gesell at 3.4 years: 37). Speech was severely impaired with the first words pronounced at the age of 2 years. At his present age, he still cannot communicate or pronounce phrases. His behavior is characterized by hyperactivity and autistic features. He presents obsessionality such as a special interest in whirligigs.

Supplementary Note 13
Patient 13 is a 3-year-old girl born preterm at 30 weeks of gestation, because of maternal preeclampsia, by normal delivery. At birth, her OFC was 33 cm (15 th centile). She had postnatal deceleration of head growth and at the age of 2 years and 9 months OFC was 42.5 cm (<3 rd centile). During the second month of life, she started experiencing focal myoclonic seizures, with eyelid myoclonus and chewing. EEG showed prominent spike and slow spikes over the right centrotemporal region. At this stage, myoclonic and clonic seizures occurred between 15 and 40 times per day. She never reached any motor milestone or made visual contact. She also had feeding difficulties. Several antiepileptic treatments, including clonazepam, topiramate, phenobarbital, and ketogenic diet failed to improve her epilepsy. Since the second year of life, asymmetrical dystonia and dyskinesia were also noted. Neurological examination at the age of 2 years revealed severe hypotonia associated with spasticity. Brain imaging showed generalized reduction in the cerebral white matter volume and cerebellar atrophy with vermian deficiency (Fig. 2 d-f). WES revealed a de novo missense variant in GRIA2 (NM000826.3: c.1937C>A; p.Thr646Asn).

Supplementary Note 14
Patient 14 is an 8-year-old girl from Korea. Her first symptoms started during early infancy with severe hypotonia and developmental delay. She has severe ID. Her motor milestones were delayed and she never walked although she is able to sit without support. She presented autistic features and aggressive behaviour since early childhood. She also has emotional lability with inappropriate screaming or crying. She has no purposeful movements of the hands. She also has a history of difficulty falling sleep. Her speech impairment is severe, and she never pronounced intelligible words. Trio WES identified a de novo missense variant in GRIA2 (NM000826.3: c.1932C>A; p.Phe644Leu).

Supplementary Note 15
Patient 15 is a 13-year-old Chinese Han girl with ASD and ID. There is no history of neurological disorders in the family. During her infancy she was diagnosed with speech and development delay, and abnormal behavior with hyperactivity and autistic features. There is no history of seizures. MIPs identified a de novo missense variant in GRIA2 (NM000826.3:c.140G>A; p.Gly47Glu).

Supplementary Note 16
Patient 16 is a 9-year-old boy with developmental and epileptic encephalopathy. At birth, his OFC was 35 cm (30 th centile). During the first week of life, benign neonatal sleep myoclonus was noted. At the age of 3 months episodes of trunk and arms stiffness triggered by intercurrent illness were observed. At the age of 6 months he was diagnosed with epileptic spasms. At this stage, spasms occurred in cluster and with a daily frequency. Other seizure types included tonic and tonic-clonic seizures, status epilepticus and focal impaired awareness seizures (FIAS). At 7 months, video-EEG showed FIAS with either left or right frontal origin.
The patient exhibited profound delay in motor milestones and did not reach the ability to walk. Also there is a history of regression of previously acquired abilities such as smiling, rolling and grasping. He is able to make visual contact and to follow. Several antiepileptic treatments including phenobarbitone, phenytoin, popiramate, clonazepam, levetiracetam, valproic acid and oxcarbazepine, failed to control his epilepsy, although an improvement with ketogenic diet (given with phenytoin, topiramate, phenobarbitone and clonazepam) was observed. Follow-up EEG at the age of 7 years showed bilateral epileptiform activity (left > right) and an abnormally slow background. Episodes of intermittent eye and head deviation to right, intermittent facial jerking, abnormal movements of upper and lower limb without EEG correlate were also noticed. Brain imaging showed a mild progressive cerebral atrophy (brain imaging not shown). Proband-father WES revealed a missense variant in GRIA2 (NM_000826.3: c.1939G>C; p.Val647Leu) which was confirmed de novo through targeted sequencing in the mother. Paternity and maternity were confirmed via targeted sequencing.

Supplementary Note 17
This is a 3-month-old Ashkenazi Jewish boy born at term after an uneventful pregnancy and normal delivery. Birth weight was 3.16 kg and OFC was 34.5 cm (25 th centile). At the age of 3 months OFC was 38.5 cm (10 th centile). After birth he had an episode of apnoea associated with low muscle tone and respiratory insufficiency. He was then intubated and phenobarbital treatment was given because of suspected seizures. At day 4 of life his neurological examination revealed myoclonus in the face and limbs. However, at that time the EEG showed normal background activity with no epileptic activity. He was started on clonazepam in addition to the phenobarbital. At day 7 of life he started suffering from focal seizures characterized by eye blinking and mastication, sometimes associated with hypertonia and bradycardia. Episodes of increased tone, bradycardia, and breathing abnormalities (with short of apnoea) were observed in the first weeks of life. An exaggerated startle response was noted. EEG showed bilateral, mainly temporal, non-synchronized epileptic activity with multiple focal ictal electrographic events. A metabolic and genetic work-up was then performed and reported as normal. Magnetic resonance imaging (MRI) of the brain revealed cerebellar vermis hypoplasia, with otherwise normal brain structure . Several AEDs, including phenytoin, carbamazepine, clonazepam, topiramate, levetiracetam, valproic acid, pyridoxine, pyridoxal 5-phosphate, vigabatrin, ketamine, lacosamide, and perampanel failed to control his seizures. At age 2.5 months, he was on ketogenic diet, phenobarbital, clonazepam, and topiramate. Clinical examination demonstrated microcephaly (OFC 38.5 cm, < 5 th ) and marked (especially axial) hypotonia. He was noted to have some visual contact but did not reach any motor or developmental milestones. At the age of 3 months he expired (probable SUDEP). Post-mortem trio WES identified a de novo missense variant in GRIA2 (NM_000826.3: c.1915G>T; P.Ala639Ser).

Supplementary Note 18
Patient 17 is a 5-year-old Caucasian boy born at term after uneventful pregnancy and delivery by caesarean section. Weight and height at birth were within normal ranges and OFC was 35 cm (25 th centile). On day 4 of life he had episodes of clonus of the right upper limb with post-ictal hypotonia. At that time EEG and brain imaging were reported as normal. During the first 3 months of life, he presented focal motor seizures involving the right face and upper limb associated with brief (several seconds) loss of consciousness. Subsequently in his infancy and childhood the seizures evolved to a pattern characterized either by fixed gaze with upper limb extensor posturing and breathing changes or, alternatively, frequent tonic attacks (every 2-3 days) characterized by extension of all four limbs associated with staring and abnormal breathing and sialorrhea. At his last clinical examination at the age of 5 years, he has choreo-athetoid movements and lower limbs spasticity. Intermittent strabismus and some abnormal ocular movements are also noted. The head and neck control are normal. Visual interaction is inconstant and brief. The frequency of seizures varies between daily and weekly, with left upper limb and right face clonus. Brain imaging (Fig. 2 jl) shows global cerebral atrophy with vermian atrophy and white matter changes. EEG shows very slow rhythms with frontal-central delta activity and left frontal discharges. At his current age of 5 years his OFC is 49 cm (15 th centile). Several antiepileptic medications have been trialled including phenobarbital, phenytoin, vigabatrin, midazolam, and valproic acid with poor results. Epilepsy improved slightly after the introduction of clonazepam and levetiracetam. He started vocalization although cannot say any intelligible word. Trio WES identified a de novo GRIA2 variant (NM_000826.3: c.1939G>C; p.Val647Leu).

Supplementary Note 19
This patient is a 5-year-old Chinese Han boy with ASD and ID. There is no history of neurological disorders in the family. During his infancy he was diagnosed with speech delay and delay in development milestones. He has intellectual disability (at the age of 4.5 years non-verbal intellectual quotient: 74; verbal intellectual quotient: 88) and, since the third year of life, abnormal behavior with autistic features and obsessive-compulsive traits was noted. He exhibit hand and finger mannerisms. There is no history of seizures. MIPs identified a de novo stop-gain variant in GRIA2 (NM000826.3: c.967C>T; p.Arg323ter).

Supplementary Note 20
This is a 5-month-old Brazilian female, born by cesarean section after uneventful pregnancy. At birth, she had Apgar score of 9, weight of 3090 g and OFC of 35cm (50-75 th ). Since the first day of life she developed focal erratic seizures with facial grimacing and abnormal ocular movements. She also had frequent episodes of brief clonic seizures associated with associated cyanosis and respiratory difficulties. The girl remained most of her life artificially ventilated, initially with orotracheal tube and lately with tracheostomy. She also had feeding difficulties and required nasogastric tube and then gastrostomy at 2 months of age. Several antiepileptic trials were trialled including phenobarbital, valproic acid, topiramate, vigabatrin, levetiracetam pyridoxine and pyrodoxal phosphate failed to control her seizures. She did not reach any motor or developmental milestones. Brain MRI imaging showed a marked cortico-subcortical and cerebellar atrophy at the age of 2 months (not shown). Several EEG were performed, and these showed heterogeneous abnormal patterns including burstsuppression like pattern at seizures onset and multifocal spikes (more intense in temporal regions) on follow-up EEGs. At the age of 5 months she expired (probable SUDEP). Post-mortem trio WES analysis identified a de novo missense variant in GRIA2 (NM_000826.3: c.1915G>T; P.Ala639Ser).

Supplementary Note 21
This is a 3-year-old Dutch boy with developmental epileptic encephalopathy. At birth, his OFC was 33 cm (15 th ). At the age of 2 years and 9 months OFC was 46 cm (<3 rd centile). Shortly after birth right sided focal clonic seizures (with associated contralateral deviation of the head) were noticed. Other seizure types observed during the first months of life included tonic clonic, focal, and focal with secondary generalisation. Seizures usually occurred in cluster of multiple episodes (2-6) a day and were often preceded by staring and blinking with eyes. The boy also had global developmental delay and at the current age he is still unable to sit unsupported. He is non-verbal. Several antiepileptic treatments including phenobarbital, Levetiracetam and valproic acid were trialled with a good clinical response although fever-associated seizures still occur. EEG at onset showed focal discharges over the frontal and parietal areas and an abnormally slow background. Follow-up EEG showed intermittent series of discharges of high amplitude with a maximum over the fronto-central areas (left>right). Brain MRI was reported as normal. Trio WES revealed a de novo missense variant in GRIA2 (NM_000826.3: c.1939G>C; p.Val647Leu).

Supplementary Note 22
Patient 22 is a 3-year-old boy with mild developmental delay and intellectual disability, some autistic features including hand clapping and repetitive behaviours. He has a mixed expressive receptive language disorder with limited functional communication, inability to express needs and echolalia. EEG and brain MRI were normal. WES identified a de novo missense variant in GRIA2 (NM_000826.3: c.2435A>G; p.Asn812Ser).

Supplementary Note 23
Patient 23 is a 30-year-old female with intellectual disability and an history of developmental delay. Since her infancy she had poor eye contact, inappropriate social interaction and repetitive behaviours, which led to a diagnosis of autism spectrum disorder. She has not attained an intelligible speech. She also has echolalia and motor stereotypies. She suffered from insomnia. Her brain MRI was normal. At the age of 8 years she developed a single episode of generalized tonic seizures, at that time valproic acid treatment was started and no further seizure episodes occurred. Trio WES identified a de novo missense variant in GRIA2 (NM_000826.3: c.2328G>T; p.Glu776Asp).

Supplementary Note 24
Patient 24 is a 5-year-old male with an history of developmental delay. He became able to sit unassisted at the age of 12 months; at the current age of 5 years, he can crawl but cannot walk or stand unassisted. He has not attained any intelligible speech. At the age of 6 months, short-lasting (around 30 seconds) episodes of drooling, lip retraction, and gaze deviation (without post-ictal symptoms) were observed. Sometimes these episodes were longer and progressed to clonic jerking. EEG at onset showed bilateral right frontal epileptic discharges, consistent with a diagnosis of focal seizures. Follow-up EEGs showed multifocal epileptiform abnormalities, on abnormal slowed background. Several antiepileptic drugs were trialled including phenobarbital, levetiracetam, oxcarbazepine and topiramate but these failed to control his seizures. Brain MRI showed a generalized mild atrophy of cerebral parenchymal and white matter loss; also, hippocampal formations appeared to be small (not shown). Trio WES revealed a de novo missense variant in GRIA2 (NM_000826.3: c.1939G>C; p.Val647Leu).

Supplementary Note 25
Patient 25 is a 3 year and 6 months old girl from Canada. Her first symptoms started during early infancy with hypotonia and developmental delay. Her motor milestones were delayed: she sat unassisted at 12 months, crawled at 20 months and walked at the age of 32 months. At 2 months of age she presented with a cluster of apparently generalized tonic-clonic seizures and was put under valproic acid. At that time, EEG showed multifocal epileptiform activity central-parietal EEG showed multifocal epileptiform activity mainly in the left temporal regions. Since the first year of life autistic features including abnormal behaviour and stereotyped movements (including hand wringing) were noticed. She is non-verbal. At present, her seizures are described as brief focal <1 minute, 1-2 per day with staring, eye deviation and (left) facial twitching. She may also have occasional generalized tonic-clonic seizures. Several antiepileptic treatments including phenobarbitone, phenytoin, clonazepam, levetiracetam, topiramate, valproic acid, oxcarbazepine and cannabinoids failed to control her epilepsy. Trio WES identified a de novo missense variant in GRIA2 (NM000826.3: : c.2420C>T; p.A807V).

Supplementary Note 26
This is a 6-year-old British girl with a history of developmental delay since infancy. She started walking at the age of 18 months. She said her first word at the age of 2 years. She has ASD and abnormal behavior. Clinical examination reveals joint hyper-mobility. There is no history of seizures or of any neurological disorders in the family. At the current age of 6 years her height is 101.5cm (25th centile) and OFC is 50.5cm (between 10th and 25th centile). Microarray analysis identified a de novo microdeletion [hg19] 4q32.1 (156,351,983,901) x1dn encompassing 8 coding genes including GRIA2.

Supplementary Note 27
This is a 12-year-old Italian girl with a history of developmental delay since infancy. She started walking at the age of 18 months, and her first words were at 2 years. She was diagnosed with ID, ASD and abnormal behavior. Examination reveals joint hyper-mobility and club feet. There is no history of seizures and EEG at the age of 4 years was reported as normal. Brain imaging was also normal. She has severely impaired speech and currently is non-verbal. Microarray analysis showed a de novo microdeletion [hg19] 4q32.1 (153,038,154-159,949,244)x1dn including GRIA2.

Supplementary Note 28
Patient 20 is a 13-year-old Caucasian boy who presented since in early infancy with mild developmental delay and abnormal behavior. At the age of 4 years his OFC was 50.5 cm (25 th centile). At the latest cognitive evaluation at the age of 11 years his intellectual quotient (QI)

Molecular dynamic stimulations
To compare the structural mobility of GluA2 and its mutants we built a model of each protein ectodomain including an LBD and an ATD (Online Methods) by modelling mutations on the wildtype, and followed their behaviour along time by means of atomistic molecular dynamics simulations in water solvent. Proteins with mutations in the pore region where omitted as either the mutations were close to or included in the transmembrane domains (TMDs) which were not modelled. We aimed to ascertain the effect of the mutations on the glutamate (GLU) binding-pocket. Interestingly, in the studied mutated proteins this group of atoms appear to have a higher level of rigidity compared to the wild-type protein. While the wild-type crystal structure is symmetric, after 10 ns the conformations of pockets associated with chains C and D, which are coupled in the binding site, diverge with respect to those associated with A and B which do not change conformation. In the observed timeframe molecules underwent concerted macroscopic movements and this is reflected by minor variations in their backbone root mean squared deviation (RMSD, Supplementary Figure 9) and radius of gyration (Supplementary Figure 10).The RMSD, which is a measure of the average atoms displacement from the starting configuration, clearly indicates that amino acids in the GLU binding site are independently mobile at a timescale consistent with our simulations with two pockets reaching values larger than 0.27nm. However, the same is not true for most mutants: p.D302G, p.F644L, p.P528T and p.V647L whose RMSD do not exceed 0.22nm. The remaining mutants studied showed an intermediate behaviour.

Supplementary Figure2. Sanger sequences of kindreds with de-novo GRIA2 intragenic variants.
Chromatograms of patients 1-18 (a-r) and their parents confirm the de-novo occurrence of the GRIA2 variants in all cases. M/+ denotes the indicated novel GRIA2 variant in the heterozygous state, and +/+ denotes homozygous wild-type sequence. Mutant bases are indicated by a red arrow.

Supplementary Figure 3. Multiple alignments of the amino acids altered by the identified GRIA2 intragenic variants across glutamate receptor subunit homologue genes.
Multiple alignments showing partial to complete conservation the mutated GluA2 residues (bold in red and highlighted in yellow) across homologue ionotropic glutamate receptor subunits. All the intragenic missense variants identified in this study affect conserved residues of GluA2 (GERP ++ > 4, see Supplementary Table 1

Supplementary Figure 6. Additional quantification of western blots.
Total cell input and biotinylated pull-down fraction were quantified relative to GADPH and then normalised to a WT control on the same gel for both GluA1 (a) and GluA2 (b). Surface protein was quantified as PD/IN for GluA1 (c) * p<0.05, **p<0.01 vs WT.

Supplementary Figure 7. Additional non-clinical mutants included for comparison.
We tested I375V, the most common variant of GluA2 not associated with a specific disease, and A643T, which is homologous to the Lurcher mutation which has been studied in other iGluRs. (a) Homomeric GluA2 had altered maximal current for both mutations. Holding current was not affected. Co-expression of I375V with GluA1 did not reveal differences in amplitude (b) or rectification.   -------  Abnormal muscle tone --+ -+ + Diminished response to pain n/a -n/a n/a n/a n/a Gait dyspraxia or absent gait -- n/a Slow background, poor organization n/a n/a n/a n/a n/a n/a Central visual impairment Yes No Yes No n/a n/a n/a n/a n/a

Photosensitivity No No
No n/a n/a No n/a n/a n/a