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A Case of ALG6-CDG with Explosive Onset of Intractable Epilepsy During Infancy

ALG6-CDG is a rare, but second most common, type 1 congenital disorder of glycosylation (CDG) caused by a defect in the α-1-3-glucosyltransferase (ALG6) enzyme in the N-glycan assembly pathway. Many mutations have been identified and inherited in an autosomal recessive pattern. There are less than 100 ALG6-CDG cases reported, all sharing the phenotype of hypotonia and developmental delay. The majority (perhaps >70%) have seizures, but a minority have intractable epilepsy or epileptic encephalopathy. We report the clinical course, EEG findings, and neuroimaging of a child found to have compound heterozygous alleles c.257 + 5G > A and c.680G > A (p.G227E) who developed explosive onset of intractable epilepsy and epileptic encephalopathy. Initially, CDG was not suspected due to its rarity and lack of multi-organ system involvement, but rapid whole exam sequence (8-day turnaround) revealed the specific diagnosis quickly.