Distinct effects on mRNA export factor GANP underlie neurological disease phenotypes and alter gene expression depending on intron content.

Defects in the mRNA export scaffold protein GANP, encoded by the MCM3AP gene, cause autosomal recessive early-onset peripheral neuropathy with or without intellectual disability. We extend here the phenotypic range associated with MCM3AP variants, by describing a severely hypotonic child and a sibling pair with a progressive encephalopathic syndrome. In addition, our analysis of skin fibroblasts from affected individuals from seven unrelated families indicates that disease variants result in depletion of GANP except when they alter critical residues in the Sac3 mRNA binding domain. GANP depletion was associated with more severe phenotypes compared with the Sac3 variants. Patient fibroblasts showed transcriptome alterations that suggested intron content-dependent regulation of gene expression. For example, all differentially expressed intronless genes were downregulated, including ATXN7L3B, which couples mRNA export to transcription activation by association with the TREX-2 and SAGA complexes. Our results provide insight into the molecular basis behind genotype-phenotype correlations in MCM3AP-associated disease and suggest mechanisms by which GANP defects might alter RNA metabolism.

Ataxia.

The approach to the child with ataxia requires a detailed history and careful general and neurological examination as well as selected blood work and brain imaging and increasingly available genetic testing for inherited ataxias that usually have an episodic or progressive presentation. The differential of acute and recurring ataxia covered in this chapter includes intoxication (e.g., antiepileptics, lead, alcohol), postinfectious cerebellitis, hemorrhage, ischemic stroke, tumor (posterior fossa or cerebellum), brainstem encephalitis, occult neuroblastoma, Miller Fisher syndrome, conversion reaction, multiple sclerosis, epileptic pseudoataxia, vasculitis (e.g., Kawasaki), metabolic etiologies (e.g., maple syrup urine disease, pyruvate dehydrogenase deficiency, ornithine transcarbamylase deficiency, biotinidase deficiency, Hartnup disease, and argininosuccinic aciduria), migraine, migraine equivalents (benign paroxysmal positional vertigo), autosomal dominant episodic ataxias (with seven types currently identified), and hypothyroidism. Cooperation with therapists and providers from other specialties including ophthalmology and genetics and metabolism is essential to caring for these children and their families.

Two patients with an anti-N-methyl-D-aspartate receptor antibody syndrome-like presentation and negative results of testing for autoantibodies.

We describe two boys whose distinct and remarkable clinical pictures suggested the possibility of anti-N-methyl-d-aspartate receptor antibody encephalitis. Both patients responded to immunotherapy, but neither manifested that antibody. Patient 1 exhibited florid encephalopathy with psychotic manifestations including inappropriate affect, intermittent delirium, visual hallucinations, severe anorexia, agitation, paranoid ideation, and abnormal electroencephalogram results. He responded to intravenous immunoglobulin, with steady improvement over 3 months to almost complete remission for 1 year, followed by a relapse that again responded, more quickly, to intravenous immunoglobulin. A second relapse occurred 1 month later, and again responded to intravenous immunoglobulin. Patient 2 exhibited progressive, severely debilitating limb dystonia that worsened over 1.5 years, with milder psychiatric symptoms including mood instability, aggressiveness, impulsivity, and depression. When he developed thymic hyperplasia 1.5 years into his illness, he underwent a thymectomy, and improved significantly on a regimen of plasmapheresis and intravenous immunoglobulin. Patients presenting with symptoms suggestive of autoimmune encephalitis, but without antibodies, may still respond to immunotherapy.

Oculogyric crises secondary to lamotrigine overdosage.

We report four patients with no preexisting movement disorders who developed oculogyric crises secondary to lamotrigine toxicity and had resolution of these crises after dose reduction. Episode numbers ranged from 1-20 per day and episode duration from 2 s to several hours. Mean plasma concentration of lamotrigine at the time of oculogyric crisis was 15.5 µg/mL, with a mean dose of 16 mg/kg per day.

Electroencephalographic and seizure manifestations of pyridoxal 5'-phosphate-dependent epilepsy.

We describe the electroencephalographic and clinical seizure manifestations of pyridoxal 5'-phosphate-dependent epilepsy (PLP-DE) in two patients [diagnosis confirmed by low cerebrospinal fluid (CSF) PLP, complete resolution of previously intractable seizures with PLP supplementation, negative pyridoxine-dependent epilepsy CSF biomarkers, and/or positive disease causing pyridox(am)ine 5'-phosphate oxidase gene mutation] along with a comprehensive review of the literature. One patient presented with neonatal tonic status epilepticus with subsequent generalized tonic-clonic seizures, and the second, with refractory complex partial seizures starting at 2 years of age. The pretreatment EEG revealed, interictally, burst suppression, multifocal independent sharp waves, and electrical status epilepticus in sleep. Ictally and interictally, it revealed runs of unilateral spike/slow waves. Previously reported features include burst suppression, myoclonus, tonic seizures, clonic seizures, and spasms. In the appropriate clinical scenario, the aforementioned features should raise the possibility of PLP-DE and appropriate treatment should be initiated. The first late-onset case (at 2 years) of PLP-DE is reported.