Neuronal deficiency of ARV1 causes an autosomal recessive epileptic encephalopathy.

We report an individual who presented with severe neurodevelopmental delay and an intractable infantile-onset seizure disorder. Exome sequencing identified a homozygous single nucleotide change that abolishes a splice donor site in the ARV1 gene (c.294 + 1G > A homozygous). This variant completely prevented splicing in minigene assays, and resulted in exon skipping and an in-frame deletion of 40 amino acids in primary human fibroblasts (NP_073623.1: p.(Lys59_Asn98del). The p.(Lys59_Asn98del) and previously reported p.(Gly189Arg) ARV1 variants were evaluated for protein expression and function. The p.(Gly189Arg) variant partially rescued the temperature-dependent growth defect in arv1Δ yeast, while p.(Lys59-Asn98del) completely failed to rescue at restrictive temperature. In contrast to wild type human ARV1, neither variant expressed detectable levels of protein in mammalian cells. Mice with a neuronal deletion of Arv1 recapitulated the human phenotype, exhibiting seizures and a severe survival defect in adulthood. Our data support ARV1 deficiency as a cause of autosomal recessive epileptic encephalopathy.

Mutations of PTPN23 in developmental and epileptic encephalopathy.

Developmental and epileptic encephalopathies (DEE) are a heterogeneous group of neurodevelopmental disorders with poor prognosis. Recent discoveries have greatly expanded the repertoire of genes that are mutated in epileptic encephalopathies and DEE, often in a de novo fashion, but in many patients, the disease remains molecularly uncharacterized. Here, we describe a new form of DEE in patients with likely deleterious biallelic variants in PTPN23. The phenotype is characterized by early onset drug-resistant epilepsy, severe and global developmental delay, microcephaly, and sometimes premature death. PTPN23 encodes a tyrosine phosphatase with strong brain expression, and its knockout in mouse is embryonically lethal. Structural modeling supports a deleterious effect of the identified alleles. Our data suggest that PTPN23 mutations cause a rare severe form of autosomal-recessive DEE in humans, a finding that requires confirmation.