Congenital myasthenic syndrome caused by a frameshift insertion mutation in GFPT1.

OBJECTIVE: Description of a new variant of the glutamine-fructose-6-phosphate transaminase 1 (GFPT1) gene causing congenital myasthenic syndrome (CMS) in 3 children from 2 unrelated families. METHODS: Muscle biopsies, EMG, and whole-exome sequencing were performed. RESULTS: All 3 patients presented with congenital hypotonia, muscle weakness, respiratory insufficiency, head lag, areflexia, and gastrointestinal dysfunction. Genetic analysis identified a homozygous frameshift insertion in the GFPT1 gene (NM_001244710.1: c.686dupC; p.Arg230Ter) that was shared by all 3 patients. In one of the patients, inheritance of the variant was through uniparental disomy (UPD) with maternal origin. Repetitive nerve stimulation and single-fiber EMG was consistent with the clinical diagnosis of CMS with a postjunctional defect. Ultrastructural evaluation of the muscle biopsy from one of the patients showed extremely attenuated postsynaptic folds at neuromuscular junctions and extensive autophagic vacuolar pathology. CONCLUSIONS: These results expand on the spectrum of known loss-of-function GFPT1 mutations in CMS12 and in one family demonstrate a novel mode of inheritance due to UPD.

Utilizing RNA and outlier analysis to identify an intronic splice-altering variant in AP4S1 in a sibling pair with progressive spastic paraplegia.

We report a likely pathogenic splice-altering AP4S1 intronic variant in two sisters with progressive spastic paraplegia, global developmental delay, shy character, and foot deformities. Sequencing was completed on whole-blood messenger RNA (mRNA) and analyzed for gene expression outliers after exome sequencing analysis failed to identify a causative variant. AP4S1 was identified as an outlier and contained a rare homozygous variant located three bases upstream of exon 5 (NC_000014.8(NM_007077.4):c.295-3C>A). Confirmed by additional RNA-seq, reverse-transcription polymerase chain reaction, and Sanger sequencing, this variant corresponded with exon 5, including skipping, altered isoform usage, and loss of expression from the canonical isoform 2 (NM_001128126.3). Previously, loss-of-function variants within AP4S1 were associated with a quadriplegic cerebral palsy-6 phenotype, AP-4 Deficiency Syndrome. In this study, the inclusion of mRNA-seq allowed for the identification of a previously missed splice-altering variant, and thereby expands the mutational spectrum of AP-4 Deficiency Syndrome to include impacts to some tissue-dependent isoforms.

Compound heterozygous mutations in SNAP29 is associated with Pelizaeus-Merzbacher-like disorder (PMLD).

Pelizaeus-Merzbacher-like disease (PMLD) is an autosomal recessive hypomyelinating leukodystrophy, which is clinically and radiologically similar to X-linked Pelizaeus-Merzbacher disease (PMD). PMLD is characterized by early-onset nystagmus, delayed development (motor delay, speech delay and dysarthria), dystonia, hypotonia typically evolving into spasticity, ataxia, seizures, optic atrophy, and diffuse leukodystrophy on magnetic resonance imaging (MRI). We identified a 12-year-old Caucasian/Hispanic male with the classical clinical characteristics of PMLD with lack of myelination of the subcortical white matter, and absence of the splenium of corpus callosum. Exome sequencing in the trio revealed novel compound heterozygous pathogenic mutations in SNAP29 (p.Leu119AlafsX15, c.354DupG and p.0?, c.2T > C). Quantitative analysis of the patient's blood cells through RNA sequencing identified a significant decrease in SNAP29 mRNA expression, while western blot analysis on fibroblast cells revealed a lack of protein expression compared to parental and control cells. Mutations in SNAP29 have previously been associated with cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma (CEDNIK) syndrome. Typical skin features described in CEDNIK syndrome, such as generalized ichthyosis and keratoderma, were absent in our patient. Moreover, the early onset nystagmus and leukodystrophy were consistent with a PMLD diagnosis. These findings suggest that loss of SNAP29 function, which was previously associated with CEDNIK syndrome, is also associated with PMLD. Overall, our study expands the genetic spectrum of PMLD.

Neonatal epileptic encephalopathy caused by de novo GNAO1 mutation misdiagnosed as atypical Rett syndrome: Cautions in interpretation of genomic test results.

Epileptic encephalopathies are childhood brain disorders characterized by a variety of severe epilepsy syndromes that differ by the age of onset and seizure type. Until recently, the cause of many epileptic encephalopathies was unknown. Whole exome or whole genome sequencing has led to the identification of several causal genes in individuals with epileptic encephalopathy, and the list of genes has now expanded greatly. Genetic testing with epilepsy gene panels is now done quite early in the evaluation of children with epilepsy, following brain imaging, electroencephalogram, and metabolic profile. Early infantile epileptic encephalopathy (EIEE1; OMIM #308350) is the earliest of these age-dependent encephalopathies, manifesting as tonic spasms, myoclonic seizures, or partial seizures, with severely abnormal electroencephalogram, often showing a suppression-burst pattern. In this case study, we describe a 33-month-old female child with severe, neonatal onset epileptic encephalopathy. An infantile epilepsy gene panel test revealed 2 novel heterozygous variants in the MECP2 gene; a 70-bp deletion resulting in a frameshift and truncation (p.Lys377ProfsX9) thought to be pathogenic, and a 6-bp in-frame deletion (p.His371_372del), designated as a variant of unknown significance. Based on this test result, the diagnosis of atypical Rett syndrome (RTT) was made. Family-based targeted testing and segregation analysis, however, raised questions about the pathogenicity of these specific MECP2 variants. Whole exome sequencing was performed in this family trio, leading to the discovery of a rare, de novo, missense mutation in GNAO1 (p. Leu284Ser). De novo, heterozygous mutations in GNAO1 have been reported to cause early infantile epileptic encephalopathy-17 (EIEE17; OMIM 615473). The child's severe phenotype, the family history and segregation analysis of variants and prior reports of GNAO1-linked disease allowed us to conclude that the GNAO1 mutation, and not the MECP2 variants, was the cause of this child's neurological disease. With the increased use of genetic panels and whole exome sequencing, we will be confronted with lists of gene variants suspected to be pathogenic or of unknown significance. It is important to integrate clinical information, genetic testing that includes family members and correlates this with the published clinical and scientific literature, to help one arrive at the correct genetic diagnosis.

Case Report: Novel mutations in TBC1D24 are associated with autosomal dominant tonic-clonic and myoclonic epilepsy and recessive Parkinsonism, psychosis, and intellectual disability.

Mutations disrupting presynaptic protein TBC1D24 are associated with a variable neurological phenotype, including DOORS syndrome, myoclonic epilepsy, early-infantile epileptic encephalopathy, and non-syndromic hearing loss. In this report, we describe a family segregating autosomal dominant epilepsy, and a 37-year-old Caucasian female with a severe neurological phenotype including epilepsy, Parkinsonism, psychosis, visual and auditory hallucinations, gait ataxia and intellectual disability. Whole exome sequencing revealed two missense mutations in the TBC1D24 gene segregating within this family (c.1078C>T; p.Arg360Cys and c.404C>T; p.Pro135Leu). The female proband who presents with a severe neurological phenotype carries both of these mutations in a compound heterozygous state. The p.Pro135Leu variant, however, is present in the proband's mother and sibling as well, and is consistent with an autosomal dominant pattern linked to tonic-clonic and myoclonic epilepsy. In conclusion, we describe a single family in which TBC1D24 mutations cause expanded dominant and recessive phenotypes. In addition, we discuss and highlight that some variants in TBC1D24 might cause a dominant susceptibility to epilepsy.

A de novo missense mutation in ZMYND11 is associated with global developmental delay, seizures, and hypotonia.

Recently, mutations in the zinc finger MYND-type containing 11 (ZMYND11) gene were identified in patients with autism spectrum disorders, intellectual disability, aggression, and complex neuropsychiatric features, supporting that this gene is implicated in 10p15.3 microdeletion syndrome. We report a novel de novo variant in the ZMYND11 gene (p.Ser421Asn) in a patient with a complex neurodevelopmental phenotype. The patient is a 24-yr-old Caucasian/Filipino female with seizures, global developmental delay, sensorineural hearing loss, hypotonia, dysmorphic features, and other features including a happy disposition and ataxic gait similar to Angelman syndrome. In addition, this patient had uncommon features including eosinophilic esophagitis and multiple, severe allergies not described in similar ZMYND11 cases. This new case further supports the association of ZMYND11 with autistic-like phenotypes and suggests that ZMYND11 should be included in the list of potentially causative candidate genes in cases with complex neurodevelopmental phenotypes.

Secreted amyloid precursor protein-alpha upregulates synaptic protein synthesis by a protein kinase G-dependent mechanism.

Secreted amyloid precursor protein-alpha (sAPPalpha) is a neuroprotective and neurotrophic protein derived from the parent APP molecule. We have shown that sAPPalpha enhances long-term potentiation in vivo and can restore spatial memory in rats whose endogenous sAPPalpha production is impaired. These observations imply that the reduction of sAPPalpha levels seen in Alzheimer's disease, which occurs alongside increased levels of toxic amyloid-beta, may be aetiologically significant. The mechanism by which sAPPalpha brings about changes in plasticity at synapses remains unresolved. We hypothesised that sAPPalpha may stimulate changes in synaptodendritic protein synthesis, an important mechanism for normal plasticity. To test this hypothesis, we investigated the effect of sAPPalpha on protein synthesis in synaptoneurosomes prepared from the hippocampi of adult male Sprague-Dawley rats. sAPPalpha (10nM) significantly increased de novo protein synthesis as measured by the incorporation of [(35)S]-methionine into acid-insoluble proteins. This was dose-dependent and blocked completely by inhibitors of protein synthesis (cycloheximide) and of cGMP-dependent protein kinase (KT5823). Inhibitors of calcium/calmodulin-dependent protein kinases (KN62) and mitogen-activated protein kinase (PD98059) partially blocked the response. Further, the sAPPalpha-induced increase in protein synthesis was significantly attenuated when measured in synapses isolated from aged rats. These observations imply de novo protein synthesis at synapses may contribute to the long-lasting modulatory effects of sAPPalpha on synaptic plasticity.