Strehlow et al. describe the largest cohort to date of individuals with GRIN2A-related disorders. The results reveal two phenotypic subgroups associated with different classes of variants affecting ...distinct domains of the GluN2A protein with different functional consequences. The findings will help predict outcomes in newly diagnosed individuals.
Abstract
Alterations of the N-methyl-d-aspartate receptor (NMDAR) subunit GluN2A, encoded by GRIN2A, have been associated with a spectrum of neurodevelopmental disorders with prominent speech-related features, and epilepsy. We performed a comprehensive assessment of phenotypes with a standardized questionnaire in 92 previously unreported individuals with GRIN2A-related disorders. Applying the criteria of the American College of Medical Genetics and Genomics to all published variants yielded 156 additional cases with pathogenic or likely pathogenic variants in GRIN2A, resulting in a total of 248 individuals. The phenotypic spectrum ranged from normal or near-normal development with mild epilepsy and speech delay/apraxia to severe developmental and epileptic encephalopathy, often within the epilepsy-aphasia spectrum. We found that pathogenic missense variants in transmembrane and linker domains (misTMD+Linker) were associated with severe developmental phenotypes, whereas missense variants within amino terminal or ligand-binding domains (misATD+LBD) and null variants led to less severe developmental phenotypes, which we confirmed in a discovery (P = 10−6) as well as validation cohort (P = 0.0003). Other phenotypes such as MRI abnormalities and epilepsy types were also significantly different between the two groups. Notably, this was paralleled by electrophysiology data, where misTMD+Linker predominantly led to NMDAR gain-of-function, while misATD+LBD exclusively caused NMDAR loss-of-function. With respect to null variants, we show that Grin2a+/− cortical rat neurons also had reduced NMDAR function and there was no evidence of previously postulated compensatory overexpression of GluN2B. We demonstrate that null variants and misATD+LBD of GRIN2A do not only share the same clinical spectrum (i.e. milder phenotypes), but also result in similar electrophysiological consequences (loss-of-function) opposing those of misTMD+Linker (severe phenotypes; predominantly gain-of-function). This new pathomechanistic model may ultimately help in predicting phenotype severity as well as eligibility for potential precision medicine approaches in GRIN2A-related disorders.
Hyperprolinemia type I (HPI) results from a deficiency of proline oxidase (POX), involved in the first step in the conversion of proline to glutamate. Diverse phenotypes were described in patients ...with HPI, prior to the identification of the POX gene (
PRODH): whereas various patients were asymptomatic, others had neurological and extraneurological defects. The
PRODH gene is located in the region deleted in velocardiofacial syndrome (VCFS). Heterozygous and homozygous mutations have been identified in patients with variable hyperprolinemia and various features (patients with schizophrenia, chromosome 22q11 microdeletions and/or neurological defects). A functional study has divided the
PRODH missense mutations into three groups: those leading to mild, moderate, or severe reduction of POX activity. In this study, we report four unrelated children with HPI and a homogeneous severe neurological phenotype. We identified biallelic abnormalities in
PRODH in these patients that led to severe reduction of POX activity. These included missense and non-sense mutations, deletions of
PRODH and a 22q11 microdeletion. Four other children have been reported with severe biallelic
PRODH mutations. The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy. Their values of hyperprolinemia ranged from 400 to 2200
μmol/L. Patients with biallelic
PRODH alterations resulting in severely impaired POX activity had an early onset and severe neurological features. Thus, children with this phenotype and those with a microdeletion in chromosome 22q11, especially those with mental retardation and autistic features, should be tested for hyperprolinemia. Hyperprolinemic patients should be screened for
PRODH mutations.
The aim of the study was to redefine the phenotype of Allan–Herndon–Dudley syndrome (AHDS), which is caused by mutations in the SLC16A2 gene that encodes the brain transporter of thyroid hormones. ...Clinical phenotypes, brain imaging, thyroid hormone profiles, and genetic data were compared to the existing literature. Twenty‐four males aged 11 months to 29 years had a mutation in SLC16A2, including 12 novel mutations and five previously described mutations. Sixteen patients presented with profound developmental delay, three had severe intellectual disability with poor language and walking with an aid, four had moderate intellectual disability with language and walking abilities, and one had mild intellectual disability with hypotonia. Overall, eight had learned to walk, all had hypotonia, 17 had spasticity, 18 had dystonia, 12 had choreoathetosis, 19 had hypomyelination, and 10 had brain atrophy. Kyphoscoliosis (n=12), seizures (n=7), and pneumopathies (n=5) were the most severe complications. This study extends the phenotypic spectrum of AHDS to a mild intellectual disability with hypotonia. Developmental delay, hypotonia, hypomyelination, and thyroid hormone profile help to diagnose patients. Clinical course depends on initial severity, with stable acquisition after infancy; this may be adversely affected by neuro‐orthopaedic, pulmonary, and epileptic complications.
What this paper adds
Mild intellectual disability is associated with SLC16A2 mutations.
A thyroid hormone profile with a free T3/T4 ratio higher than 0.75 can help diagnose patients.
Patients with SLC16A2 mutations present a broad spectrum of neurological phenotypes that are also observed in other hypomyelinating disorders.
Axial hypotonia is a consistent feature of Allan–Herndon–Dudley syndrome and leads to specific complications.
What this paper adds
Mild intellectual disability is associated with SLC16A2 mutations.
A thyroid hormone profile with a free T3/T4 ratio higher than 0.75 can help diagnose patients.
Patients with SLC16A2 mutations present a broad spectrum of neurological phenotypes that are also observed in other hypomyelinating disorders.
Axial hypotonia is a consistent feature of Allan–Herndon–Dudley syndrome and leads to specific complications.
IFIH1 gain‐of‐function has been reported as a cause of a type I interferonopathy encompassing a spectrum of autoinflammatory phenotypes including Aicardi–Goutières syndrome and Singleton Merten ...syndrome. Ascertaining patients through a European and North American collaboration, we set out to describe the molecular, clinical and interferon status of a cohort of individuals with pathogenic heterozygous mutations in IFIH1. We identified 74 individuals from 51 families segregating a total of 27 likely pathogenic mutations in IFIH1. Ten adult individuals, 13.5% of all mutation carriers, were clinically asymptomatic (with seven of these aged over 50 years). All mutations were associated with enhanced type I interferon signaling, including six variants (22%) which were predicted as benign according to multiple in silico pathogenicity programs. The identified mutations cluster close to the ATP binding region of the protein. These data confirm variable expression and nonpenetrance as important characteristics of the IFIH1 genotype, a consistent association with enhanced type I interferon signaling, and a common mutational mechanism involving increased RNA binding affinity or decreased efficiency of ATP hydrolysis and filament disassembly rate.
Exacerbation of hyperkinesia is a life-threatening complication of dyskinetic movement disorders, which can lead to multi-organ failure and even to death. GNAO1 has been recently identified to be ...involved in the pathogenesis of early infantile epileptic encephalopathy and movement disorders. Patients with GNAO1 mutations can present with a severe, progressive hyperkinetic movement disorder with prolonged life-threatening exacerbations, which are refractory to most anti-dystonic medication.
The objective was to investigate the evolution of symptoms and the response to deep brain stimulation of the globus pallidus internus (GPi-DBS) in patients with different GNAO1 mutations.
We report six patients presenting with global motor retardation, reduced muscle tone and recurrent episodes of severe, life-threatening hyperkinesia with dystonia, choreoathetosis, and ballism since early childhood. Five of them underwent GPi-DBS.
The genetic workup revealed mutations in GNAO1 for all six patients. These encompass a new splice site mutation (c.723+1G>T) in patient 1, a new missense mutation (c.610G>C; p.Gly204Arg) in patient 2, a heterozygous mutation (c.625>T; p.Arg209Cys) in patients 3 and 4, and a heterozygous mutation (c.709G>A; p.Glu237Lys) in patients 5 and 6. By intervention with GPi-DBS the severe paroxysmal hyperkinetic exacerbations could be stopped in five patients. One patient is still under evaluation for neuromodulation.
In complex movement disorders of unsolved etiology clinical WES can rapidly streamline pathogenic genes. We identified two novel GNAO1 mutations. GPi-DBS can be an effective and life-saving treatment option for patients with GNAO1 mutations and has to be considered early.
•GNAO1 mutations are associated with life-threatening exacerbations of hyperkinesia.•Pallidal deep brain stimulation should be considered as first-line treatment in hyperkinetic exacerbations.•WES can rapidly streamline pathogenic mutations in disease associated genes in clinically complex movement disorders.
La plupart des patients porteurs de mutations hétérozygotes de novo dans GNAO1 présente un phénotype sévère caractérisé par une déficience intellectuelle profonde avec encéphalopathie épileptique de ...début précoce ou status dystonicus.
Décrire les caractéristiques cliniques et génétiques des patients présentant un phénotype léger associé à des mutations dans GNAO1.
Nous avons inclus des patients issus de 18 centres de références internationaux en mouvements anormaux. Les phénotypes légers étaient définis par (i) l’absence de déficience intellectuelle profonde, (ii) l’absence d’encéphalopathie épileptique, (iii) l’apparition des mouvements anormaux après l’âge de 2 ans, (iv) l’acquisition de la marche. La pathogénicité des variants était évaluée via les critères de l’American College of Medical Genetics (ACMG).
24 patients (9 hommes) issus de 20 familles furent inclus. L’âge moyen de début de la dystonie était 10,13 ans. La dystonie était focale dans 1 cas, segmentaire dans 6, multifocale dans 4 et généralisée dans 13. Une dysarthrie était observée dans 19 cas. Une déficience intellectuelle légère était présente chez 10 patients et modérée chez 2. La mutation se transmettait de façon autosomique dominante pour 3 familles et était de novo dans les 19 autres familles.
Nous rapportons ici la cohorte la plus large de patients porteurs de mutations dans GNAO1 présentant des phénotypes dystoniques légers. La dystonie prédominait à la partie supérieure du corps avec des troubles arthriques pour la majorité des patients. La plupart des mutations identifiées dans ce travail n’ont pas été précédemment rapportées dans les cas plus sévères, suggérant une possible corrélation entre certaines mutations et ces phénotypes plus légers.
Nous avons souligné l’existence d’un phénotype plus léger associé aux mutations dans GNAO1, avec des mutations héritées et un début à l’âge adulte dans certains cas.
Deficiency of adenosine deaminase 2 (DADA2) is a recently described autoinflammatory disorder. Genetic analysis is required to confirm the diagnosis. We aimed to describe the identifying symptoms and ...genotypes of patients referred to our reference centres and to improve the indications for genetic testing. DNA from 66 patients with clinically suspected DADA2 were sequenced by Sanger or next-generation sequencing. Detailed epidemiological, clinical and biological features were collected by use of a questionnaire and were compared between patients with and without genetic confirmation of DADA2. We identified 13 patients (19.6%) carrying recessively inherited mutations in ADA2 that were predicted to be deleterious. Eight patients were compound heterozygous for mutations. Seven mutations were novel (4 missense variants, 2 predicted to affect mRNA splicing and 1 frameshift). The mean age of the 13 patients with genetic confirmation was 12.7 years at disease onset and 20.8 years at diagnosis. Phenotypic manifestations included fever (85%), vasculitis (85%) and neurological disorders (54%). Features best associated with a confirmatory genotype included fever with neurologic or cutaneous attacks (odds ratio OR 10.71, p = 0.003 and OR 10.9, p < 0.001), fever alone (OR 8.1, p = 0.01), and elevated C-reactive protein (CRP) level with neurologic involvement (OR 6.63, p = 0.017). Our proposed decision tree may help improve obtaining genetic confirmation of DADA2 in the context of autoinflammatory symptoms. Prerequisites for quick and low-cost Sanger analysis include one typical cutaneous or neurological sign, one marker of inflammation (fever or elevated CRP level), and recurrent or chronic attacks in adults.
Summary
Objective
Pathogenic SLC6A1 variants were recently described in patients with myoclonic atonic epilepsy (MAE) and intellectual disability (ID). We set out to define the phenotypic spectrum in ...a larger cohort of SCL6A1‐mutated patients.
Methods
We collected 24 SLC6A1 probands and 6 affected family members. Four previously published cases were included for further electroclinical description. In total, we reviewed the electroclinical data of 34 subjects.
Results
Cognitive development was impaired in 33/34 (97%) subjects; 28/34 had mild to moderate ID, with language impairment being the most common feature. Epilepsy was diagnosed in 31/34 cases with mean onset at 3.7 years. Cognitive assessment before epilepsy onset was available in 24/31 subjects and was normal in 25% (6/24), and consistent with mild ID in 46% (11/24) or moderate ID in 17% (4/24). Two patients had speech delay only, and 1 had severe ID. After epilepsy onset, cognition deteriorated in 46% (11/24) of cases. The most common seizure types were absence, myoclonic, and atonic seizures. Sixteen cases fulfilled the diagnostic criteria for MAE. Seven further patients had different forms of generalized epilepsy and 2 had focal epilepsy. Twenty of 31 patients became seizure‐free, with valproic acid being the most effective drug. There was no clear‐cut correlation between seizure control and cognitive outcome. Electroencephalography (EEG) findings were available in 27/31 patients showing irregular bursts of diffuse 2.5‐3.5 Hz spikes/polyspikes‐and‐slow waves in 25/31. Two patients developed an EEG pattern resembling electrical status epilepticus during sleep. Ataxia was observed in 7/34 cases. We describe 7 truncating and 18 missense variants, including 4 recurrent variants (Gly232Val, Ala288Val, Val342Met, and Gly362Arg).
Significance
Most patients carrying pathogenic SLC6A1 variants have an MAE phenotype with language delay and mild/moderate ID before epilepsy onset. However, ID alone or associated with focal epilepsy can also be observed.
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