J. Lloyd Holder

SHANK3 overexpression causes manic-like behaviour with unique pharmacogenetic properties

Mutations in SHANK3 and large duplications of the region spanning SHANK3 both cause a spectrum of neuropsychiatric disorders, indicating that proper SHANK3 dosage is critical for normal brain function. However, SHANK3 overexpression per se has not been established as a cause of human disorders because 22q13 duplications involve several genes. Here we report that Shank3 transgenic mice modelling a human SHANK3 duplication exhibit manic-like behaviour and seizures consistent with synaptic excitatory/inhibitory imbalance. We also identified two patients with hyperkinetic disorders carrying the smallest SHANK3-spanning duplications reported so far. These findings indicate that SHANK3 overexpression causes a hyperkinetic neuropsychiatric disorder. To probe the mechanism underlying the phenotype, we generated a Shank3 in vivo interactome and found that Shank3 directly interacts with the Arp2/3 complex to increase F-actin levels in Shank3 transgenic mice. The mood-stabilizing drug valproate, but not lithium, rescues the manic-like behaviour of Shank3 transgenic mice raising the possibility that this hyperkinetic disorder has a unique pharmacogenetic profile.

Zonisamide in the treatment of epilepsy

Introduction: Epilepsy affects approximately 3 million people in the USA and up to 2% of the worldwide population. The yearly direct medical cost of epilepsy in the USA alone is estimated to be

TBC1D24 genotype–phenotype correlation: Epilepsies and other neurologic features

9.5 billion. Epilepsy affects both children and adults and can significantly impair quality of life. Zonisamide is a second-generation antiepileptic drug (AED) that has broad-spectrum efficacy, a favorable side-effect profile and simpler dosing than earlier drugs. Areas covered: The history of the development of zonisamide is reviewed in this paper. The data available demonstrating zonisamides mechanism of action as a voltage-gated sodium channel inhibitor, a T-type calcium channel inhibitor, an enhancer of GABA release and an inhibitor of glutamate release are also reviewed. Four key Phase III clinical trials are reviewed in detail, as are subsequent postmarketing trials that have expanded the therapeutic indication for zonisamide. Expert opinion: From the available clinical data, zonisamide is a viable first-line and adjunctive therapeutic for partial-onset epilepsy and should be considered as an adjunctive therapeutic for a wide-range of generalized epilepsies.

Delineation of candidate genes responsible for structural brain abnormalities in patients with terminal deletions of chromosome 6q27

Objective: To evaluate the phenotypic spectrum associated with mutations in TBC1D24. Methods: We acquired new clinical, EEG, and neuroimaging data of 11 previously unreported and 37 published patients. TBC1D24 mutations, identified through various sequencing methods, can be found online (http://lovd.nl/TBC1D24). Results: Forty-eight patients were included (28 men, 20 women, average age 21 years) from 30 independent families. Eighteen patients (38%) had myoclonic epilepsies. The other patients carried diagnoses of focal (25%), multifocal (2%), generalized (4%), and unclassified epilepsy (6%), and early-onset epileptic encephalopathy (25%). Most patients had drug-resistant epilepsy. We detail EEG, neuroimaging, developmental, and cognitive features, treatment responsiveness, and physical examination. In silico evaluation revealed 7 different highly conserved motifs, with the most common pathogenic mutation located in the first. Neuronal outgrowth assays showed that some TBC1D24 mutations, associated with the most severe TBC1D24-associated disorders, are not necessarily the most disruptive to this gene function. Conclusions: TBC1D24-related epilepsy syndromes show marked phenotypic pleiotropy, with multisystem involvement and severity spectrum ranging from isolated deafness (not studied here), benign myoclonic epilepsy restricted to childhood with complete seizure control and normal intellect, to early-onset epileptic encephalopathy with severe developmental delay and early death. There is no distinct correlation with mutation type or location yet, but patterns are emerging. Given the phenotypic breadth observed, TBC1D24 mutation screening is indicated in a wide variety of epilepsies. A TBC1D24 consortium was formed to develop further research on this gene and its associated phenotypes.

The spectrum of epilepsy and electroencephalographic abnormalities due to SHANK3 loss-of-function mutations.

Patients with terminal deletions of chromosome 6q present with structural brain abnormalities including agenesis of corpus callosum, hydrocephalus, periventricular nodular heterotopia, and cerebellar malformations. The 6q27 region harbors genes that are important for the normal development of brain and delineation of a critical deletion region for structural brain abnormalities may lead to a better genotype–phenotype correlation. We conducted a detailed clinical and molecular characterization of seven unrelated patients with deletions involving chromosome 6q27. All patients had structural brain abnormalities. Using array comparative genomic hybridization, we mapped the size, extent, and genomic content of these deletions. The smallest region of overlap spans 1.7 Mb and contains DLL1, THBS2, PHF10, and C6orf70 (ERMARD) that are plausible candidates for the causation of structural brain abnormalities. Our study reiterates the importance of 6q27 region in normal development of brain and helps identify putative genes in causation of structural brain anomalies.

Infantile Spasms and Hyperekplexia Associated With Isolated Sulfite Oxidase Deficiency

The coincidence of autism with epilepsy is 27% in those individuals with intellectual disability.1 Individuals with loss‐of‐function mutations in SHANK3 have intellectual disability, autism, and variably, epilepsy.2‐5 The spectrum of seizure semiologies and electroencephalography (EEG) abnormalities has never been investigated in detail. With the recent report that SHANK3 mutations are present in approximately 2% of individuals with moderate to severe intellectual disabilities and 1% of individuals with autism, determining the spectrum of seizure semiologies and electrographic abnormalities will be critical for medical practitioners to appropriately counsel the families of patients with SHANK3 mutations.

A child with an inherited 0.31 Mb microdeletion of chromosome 14q32.33: Further delineation of a critical region for the 14q32 deletion syndrome†

IMPORTANCE Isolated sulfite oxidase deficiency (ISOD) causes severe intellectual disability, epilepsy, and shortened life expectancy. Intractable seizures are invariable in children with ISOD; however, to our knowledge, infantile spasms with a corresponding hypsarrhythmia pattern on electroencephalogram have never been reported. In addition, the nonepileptic paroxysmal movement disorder hyperekplexia has not previously been reported with ISOD. OBSERVATIONS We describe an infant with ISOD who initially presented with neonatal seizures, diffusion restriction noted on magnetic resonance imaging, and elevated serum S-sulfocysteine consistent with ISOD. A homozygous mutation in the SUOX gene was identified, confirming the diagnosis. Uniquely, this patient developed a profound accentuated startle response that did not have a corresponding electrographic change on electroencephalogram consistent with hyperekplexia. This was followed by a change in the childs electroencephalogram to the chaotic pattern of hypsarrhythmia and brief tonic seizures with attenuation of the hypsarrhythmia pattern characteristic of infantile spasms. CONCLUSIONS AND RELEVANCE The evolution of seizures associated with ISOD is poorly characterized because of the small number of patients. We report what we believe to be the first case of a child with ISOD who developed infantile spasms and hyperekplexia. This expands the phenotypes associated with ISOD and also should caution clinicians to not assume that all abnormal movements are seizures.

Delineation of the genetic and clinical spectrum of Phelan-McDermid syndrome caused by SHANK3 point mutations

Chromosome 14q32.3 deletions are uncommon, with most described patients harboring a ring chromosome 14. Only 15 deletions have been described not associated with ring formation or other complex chromosomal rearrangements. Here, we describe a child with the smallest deletion of chromosome 14q32.3 reported in the literature. This childs deletion encompasses at most 0.305 Mb and six genes including NUDT14, BRF1, BTBD6, PACS2, MTA1, and TEX22. He has similar clinical findings, including mild facial dysmorphisms and intellectual disability, as other individuals with much larger deletions of the terminus of the long arm of chromosome 14. This suggests that the genes deleted in our patient contribute to the 14q32 deletion syndrome.

Refinement of the postnatal growth restriction locus of chromosome 5q12‐13 deletion syndrome

BackgroundPhelan-McDermid syndrome (PMS) is a neurodevelopmental disorder characterized by psychiatric and neurological features. Most reported cases are caused by 22q13.3 deletions, leading to SHANK3 haploinsufficiency, but also usually encompassing many other genes. While the number of point mutations identified in SHANK3 has increased in recent years due to large-scale sequencing studies, systematic studies describing the phenotype of individuals harboring such mutations are lacking.MethodsWe provide detailed clinical and genetic data on 17 individuals carrying mutations in SHANK3. We also review 60 previously reported patients with pathogenic or likely pathogenic SHANK3 variants, often lacking detailed phenotypic information.ResultsSHANK3 mutations in our cohort and in previously reported cases were distributed throughout the protein; the majority were truncating and all were compatible with de novo inheritance. Despite substantial allelic heterogeneity, four variants were recurrent (p.Leu1142Valfs*153, p.Ala1227Glyfs*69, p.Arg1255Leufs*25, and c.2265+1G>A), suggesting that these are hotspots for de novo mutations. All individuals studied had intellectual disability, and autism spectrum disorder was prevalent (73%). Severe speech deficits were common, but in contrast to individuals with 22q13.3 deletions, the majority developed single words, including 41% with at least phrase speech. Other common findings were consistent with reports among individuals with 22q13.3 deletions, including hypotonia, motor skill deficits, regression, seizures, brain abnormalities, mild dysmorphic features, and feeding and gastrointestinal problems.ConclusionsHaploinsufficiency of SHANK3 resulting from point mutations is sufficient to cause a broad range of features associated with PMS. Our findings expand the molecular and phenotypic spectrum of PMS caused by SHANK3 point mutations and suggest that, in general, speech impairment and motor deficits are more severe in the case of deletions. In contrast, renal abnormalities associated with 22q13.3 deletions do not appear to be related to the loss of SHANK3.

The first international conference on SYNGAP1-related brain disorders: a stakeholder meeting of families, researchers, clinicians, and regulators

Individuals with deletions of chromosome 5q12‐13 have rarely been reported and have a range of phenotypes including postnatal growth restriction, intellectual disability, hyperactivity, and ocular abnormalities. Most individuals reported have large deletions or complex rearrangements which have made identifying genes responsible for these phenotypes challenging. Here we report an individual with a chromosome 5q12‐13 deletion with intellectual disability, hyperactivity and restricted linear growth. Based on the location of our patients deletion in relation to the previously reported deletions, we have narrowed the locus for postnatal growth restriction to less than 1 megabase. Further refinement of this locus with reports of additional individuals with deletions of this region will allow for better understanding of the gene(s) responsible for this phenotype.