The patient is a 12 month old boy who was born at term to a consanguinous couple with birth weight of 2550 grams and head circumference of 34cm. His parents brought him to a primary care physician at 2 months of age due to his poor weight gain. At 4 months, frequent seizures with staring, clonic movements of the left side limbs and truncal hypotonia developed. Therefore, the patient was referred to our hospital (children’s Medical center) for further evaluation. Neurological examinations did not show spasticity nor exaggerated deep tendon reflexes, but axial hypotonia was present. Neurological deterioration was not recognized. Awake electroencephalography (EEG) at age of 4 months showed tonic and focal seizures consisting of flattening of the background preceded by generalized and multifocal spike waves followed by diffuse slow waves. Brain magnetic resonance imaging (MRI) was performed at the time of seizure onset for further evaluation (Figure 1). Brain MRI transverse spin echo (SE) T2 weighted images at the level of midbrain and high parietal centrum semi-oval demonstrated diffuse abnormally increased signal of deep and subcortical white matter. In addition, bilateral higher signal of anterior temporal subcortical white matter in T2 weighted image compared to deep white matter suggested early cystic degeneration in these areas. Coronal SE T2 weighted image and T1 fluid attenuated inversion recovery (FLAIR) sequences at the level of posterior limb of internal capsule and dentate nuclei indicated diffuse supra and infratentorial white matter increased signals which were relatively low in T1 FLAIR. Overall findings were consistent with severe demyelination of white matter. We considered a demyelinating type of childhood leukodystrophy as the probable etiology for the clinical scenario of this patient regarding to MRI pattern involvement, early onset refractory seizures and global developmental delay. Seizures of the patient stopped with intravenous anti-epileptic medications and he was discharged 2 weeks later with phenobarbital. Basic metabolic tests were all normal; therefore performing of molecular study was discussed with parents to establish the diagnosis.
Figure 1.
A, B, Brain magnetic resonance imaging (MRI) Transverse spin echo (SE) T2 weighted images at the level of midbrain and high parietal centrum semi-ovale demonstrated diffuse abnormal increased signal of deep and subcortical white matter. Note bilateral higher signal of anterior temporal subcortical white matter in T2 weighted image comparing deep white matter which suggests early cystic degeneration in these areas (white arrows). C, D, Coronal SE T2 weighted image and T1 fluid attenuated inversion recovery (FLAIR) sequences at the level of posterior limb of internal capsule and dentate nuclei indicated diffuse supra and infratentorial white matter increased signal in T2 weighted image which is respectively low in T1 FLAIR. Overall findings are consistent with severe demyelination of white matter.
In his follow-up, truncal tone was improved with occupational therapy at the age of 6 months; however, he experienced frequent tonic seizures unresponsive to anti-epileptic drugs at 7 months of age. Therefore, the patient was admitted to pediatric intensive care unit (PICU) of our hospital for 1 month for better control of seizures. The patient was discharged from the hospital with oral phenobarbital, phenytoin and levetiracetam. By obtaining informed consent from parents blood sample of the patient was sent to laboratory for molecular studies.
Two weeks later at the age of 8.5 months the patient was hospitalized again with decreased level of consciousness and 5 to 6 times of tonic seizures per day. Meanwhile, he experienced respiratory failure in PICU. Intubation was performed; followed by tracheostomy due to long term intubation.
And now, at the age of 12 months, the patient is discharged from hospital and his seizures are under control by phenobarbital, topiramate, lamotrigine, and oxcarbazepine. His respiration is supported by mechanical ventilation through T-tube and oxygen therapy. The last systemic and neurologic examinations showed central hypotonia, microcephaly, dense cataract, global developmental delay and poor weight gain. The results of molecular studies at age 12 months showed the final diagnosis.
2.1. Whole Exome Sequencing
Genomic DNA was extracted from peripheral blood using standard protocols. Coding regions and exon-intron boundaries were enriched using Agilent SureSelect Human All Exon 50 Mb (Agilent Technologies Santa Clara, CA) according to the manufacturer’s standard protocol. Sequencing was performed by targeted-next generation sequencing (NGS) analyzer on an Illumina, Hiseq4000 (Illumina, San Diego, California, USA). Burrows-Wheeler Aligner (BWA), GATK (https://www.broadinstitute.org/gatk/) software package and SAMTools were applied to align the reads using on reference genome (hg19), variant calling and for annotation. The variants were filtered based on their frequency (minor allele frequency < 0.1) in 1000 Genome ExAC (http://exac.broadinstitute.org/) and dbSNP and EVS (http://evs.gs.washington.edu/EVS/) databases. Some online software tools including Combined Annotation Dependent Depletion (CADD) (http://cadd.gs.washington.edu/), Polyphen2 (http://genetics.bwh.harvard.edu/pph2/), SIFT (http://sift.jcvi.org/) and MutationTaster (http://www.mutationtaster.org/). The standards and guidelines for the interpretation of sequence variants based on consensus recommendation of the American college of Medical genetics and genomics (ACMG) 2015 was also used to interpret the variants (4). The proband, his parents and sister were analyzed for the found variant using Sanger sequencing. Those variants that segregated with the phenotype within the entire family were considered pathogenic.
A homozygous variant (c.922G > A) (rs372548739) was detected in EIF2B2 gene in exon 8 leading to an amino acid substitution (p.Val308Met). Sanger sequencing at position c.922 of his clinically asymptomatic parents revealed a heterozygous mutation but his sister was normal for this position; the segregation analysis confirmed the result. In addition, above mentioned software tools predicted this variant as disease causing.
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