Recurrent NUS1 canonical splice donor site mutation in two unrelated individuals with epilepsy, myoclonus, ataxia and scoliosis - a case report.

BACKGROUND:We encountered two unrelated individuals suffering from neurological disorders, including epilepsy and scoliosis. CASE PRESENTATION:Whole-exome sequencing identified the same recurrent, de novo, pathogenic variant in NUS1 [NM_138459.4:c.691 + 1C > A] in both individuals. This variant is located in the conserved cis-prenyltransferase domain of the nuclear undecaprenyl pyrophosphate synthase 1 gene (NUS1), which encodes the Nogo-B receptor, an essential catalyst for protein glycosylation. This variant was confirmed to create a new splice donor site, resulting in aberrant RNA splicing resulting in a 91-bp deletion in exon 3 in both individuals. The mutant mRNA was partially degraded by nonsense mediated mRNA decay. To date, only four de novo variants and one homozygous variant have been reported in NUS1, which cause developmental and epileptic encephalopathy, early onset Parkinson's disease, and a congenital disorder of glycosylation. Seven patients, including our two patients, have presented with epileptic seizures and intellectual disabilities. CONCLUSIONS:Our study strongly supports the finding that this recurrent, de novo, variant in NUS1 causes developmental and epileptic encephalopathy with involuntary movement, ataxia and scoliosis.

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