De Novo and Bi-allelic Pathogenic Variants in NARS1 Cause Neurodevelopmental Delay Due to Toxic Gain-of-Function and Partial Loss-of-Function Effects

Aminoacyl-tRNA synthetases (ARSs) are ubiquitous, ancient enzymes that charge amino acids to cognate tRNA molecules, the essential first step of protein translation. Here, we describe 32 individuals from 21 families, presenting with microcephaly, neurodevelopmental delay, seizures, peripheral neuropathy, and ataxia, with de novo heterozygous and bi-allelic mutations in asparaginyl-tRNA synthetase (NARS1). We demonstrate a reduction in NARS1 mRNA expression as well as in NARS1 enzyme levels and activity in both individual fibroblasts and induced neural progenitor cells (iNPCs). Molecular modeling of the recessive c.1633C>T (p.Arg545Cys) variant shows weaker spatial positioning and tRNA selectivity. We conclude that de novo and bi-allelic mutations in NARS1 are a significant cause of neurodevelopmental disease, where the mechanism for de novo variants could be toxic gain-of-function and for recessive variants, partial loss-of-function.

Splice site, frameshift, and chimeric GFAP mutations in Alexander disease

Alexander disease (AxD) is a usually fatal astrogliopathy primarily caused by mutations in the gene encoding glial fibrillary acidic protein (GFAP), an intermediate filament protein expressed in astrocytes. We describe three patients with unique characteristics, and whose mutations have implications for AxD diagnosis and studies of intermediate filaments. Patient 1 is the first reported case with a noncoding mutation. The patient has a splice site change producing an in-frame deletion of exon 4 in about 10% of the transcripts. Patient 2 has an insertion and deletion at the extreme end of the coding region, resulting in a short frameshift. In addition, the mutation was found in buccal DNA but not in blood DNA, making this patient the first reported chimera. Patient 3 has a single-base deletion near the C-terminal end of the protein, producing a short frameshift. These findings recommend inclusion of intronic splice site regions in genetic testing for AxD, indicate that alteration of only a small fraction of GFAP can produce disease, and provide caution against tagging intermediate filaments at their C-terminal end for cell biological investigations.

Rituximab (anti-CD20) adjunctive therapy for opsoclonus-myoclonus syndrome

PURPOSE

To determine if rituximab, an anti-CD20 monoclonal antibody, reduces cerebrospinal fluid (CSF) B-cell expansion in opsoclonus-myoclonus syndrome (OMS) and results in clinical improvement.

METHODS

Sixteen children with OMS and increased % CD20 B-cells in CSF received 4 rituximab infusions (375 mg/m IV) as add-on therapy to corticotropin (ACTH), intravenous immunoglobulins, or both, and were reevaluated 6 months later. Outcome measures were clinical (motor function, behavior, sleep) and immunologic (CSF and blood immunophenotype and Ig levels). Controls were 16 age-matched and sex-matched children, who did not have OMS.

RESULTS

After rituximab, 81% of OMS had a lower motor severity score, and 44% improved one severity category. Mean total score decreased by 44% (P = 0.0005). Rituximab reduced rage score, nighttime awakenings, and the number of children with opsoclonus, action myoclonus, drooling, gait ataxia, and rage. Despite a 51% reduction in ACTH dose, 9 of 11 children on ACTH did not relapse. The percentage of CSF CD19 (and CD20) B-cells was lowered in all children (undetectable in 6), with a 90% reduction in the group mean (P = 0.00003). CSF B-cells were no longer expanded compared with controls. In blood, CD19 B-cells decreased (-90%, P = 0.0003), as did the CSF:blood CD19 B-cell ratio (P = 0.00003). Serum IgM fell by 69% (below reference range), with no statistically significant change in IgG or IgA.

CONCLUSIONS

Rituximab seems efficacious and safe as adjunctive therapy for OMS. Selective targeting of CSF B lymphocytes represents a novel and valuable paradigm shift in the therapy for centrally mediated paraneoplastic disorders.

Congenital disorder of glycosylation Ic in patients of Indian origin

Congenital disorder of glycosylation type Ic (CDG-Ic) is caused by mutations in ALG6, encoding an alpha 1,3-glucosyltransferase. The most frequent mutation found in this gene (C998T resulting in an A333V substitution) has until now been found only in patients of European origin. Here we describe the first occurrence of this CDG-Ic mutation in patients of Indian origin. Of three Indian patients described in this study, patient 1 was homozygous and patient 2 heterozygous for the A333V mutation. In patient 2 we also found a new mutation, IVS3+2_3insT, just 3bp away from the previously described IVS3+5G>A substitution; both mutations resulted in exon 3 skipping. We screened a panel of >350 genomic DNA samples from an ethnically diverse American population to determine the frequency of the A333V mutation. None of the samples carried this mutation, indicating the frequency of patients carrying this homozygous mutation should be <1 in 5x10(5). The discovery of the common CDG-Ic mutation A333V in an Indian population raises questions as to its ethnic origin.

Brain dysfunction in an adolescent with the neuromuscular form of hexosaminidase deficiency

A 14-year-old girl of Ashkenazi Jewish background is described who has severe deficiency of hexosaminidase A. She presented with slowly progressive motor neuron degeneration and was found to have subtle deficiencies on neuropsychological testing, abnormal cortical evoked potentials and structural abnormalities of the cerebellum on CT scan. This patient extends the reported clinical findings for adolescents and suggests the possibility of similar abnormalities in others with neuromuscular deterioration.

'Idiopathic' neonatal cerebral infarction

Neonatal cerebral infarction is infrequently reported in the living newborn and is usually associated with perinatal risk factors, trauma, and asphyxia. This report describes two cases of full-term newborns with no predisposing problems who had unequivocal left cerebral infarctions associated with seizures in the first 24 hours of life. Radiological studies suggested an embolic cause in one case.

Failure of daily lumbar punctures to prevent the development of hydrocephalus following intraventricular hemorrhage

A prospective study of 48 infants with periventricular-intraventricular hemorrhage was carried out to evaluate the role of daily lumbar punctures, instituted from the time of diagnosis of the hemorrhage, in prevention of posthemorrhagic hydrocephalus and improvement in immediate outcome. The data lead to the following conclusions: (1) minor hemorrhage (Grade I) is associated with minimal risk of death or hydrocephalus; (2) moderate hemorrhage (Grade II) is associated with low risk of death and intermediate risk of hydrocephalus, and serial lumbar punctures do not reduce these risks; and (3) severe hemorrhage (Grade III) is associated with high risks of death or hydrocephalus or both, and serial lumbar punctures also do not reduce these risks.

Porencephaly from periventricular intracerebral hemorrhage in a premature infant

In two thirds of the premature infants who survived large periventricular intracerebral hemorrhage, a porencephalic cyst developed at the site of parenchymal hemorrhage. The porencephaly seems to develop as a result of local parenchymal destruction by the hemorrhage itself. These cysts can occur in the absence of posthemorrhagic hydrocephalus or increased intracranial pressure. Three of four infants who were observed for at least five months had lateralized motor deficit that corresponded to the cyst.

Acquired aphasia with convulsive disorder: course and prognosis

Acquired aphasia with convulsive disorder is an unusual condition in childhood, characterized by loss of language function associated with a paroxysmal electroencephalogram. To determine the course and outcome of this disorder, we evaluated nine patients 10 to 28 years after the onset of aphasia. Four patients had recovered fully, one had mild language dysfunction, and four had moderate language disability. Four of the five patients with the best outcome had decreased visuoperceptive function as measured by the Revised Benton Visual Retention Test (RBVRT), whereas the three tested patients with moderate language dysfunction had normal RBVRT scores.