SPOUT1 variants associated with autosomal-recessive developmental and epileptic encephalopathy.

Background: Developmental and epileptic encephalopathy (DEE) is a group of neurodevelopmental disorders characterized by early-onset seizures predominantly attributed to genetic causes. Nevertheless, numerous patients remain without identification of a genetic cause.

Methods: We present four unrelated Chinese patients with SPOUT1 compound heterozygous variants, all of whom were diagnosed with DEE. We also investigated functions of SPOUT1 using the spout1 knockout zebrafish model.

Results: The four unrelated DEE patients with SPOUT1 compound heterozygous variants were all males. Their onset age of seizure ranged from 3 months to 6 months (median age 5 months). All patients had epileptic spasms, and were diagnosed with infantile epileptic spasms syndrome (IESS). Three patients had microcephaly during infancy. Brain MRI in three patients showed white matter hypomyelination and bilaterally widened frontotemporal subarachnoid space. At the last follow-up, two patients exhibited drug-resistant epilepsy, one achieved seizure freedom following vigabatrin treatment, and one died at the age of 4 years and 5 months from probable sudden unexpected death in epilepsy. Seven different SPOUT1 variants were identified in the four patients, including six missense variants and one deletion variant. AlphaFold2 prediction indicated that all variants alternated the number or the length of bonds between animo acids in protein SPOUT1. Neurophysiological results from spout1 knockout zebrafish revealed the presence of epileptiform signals in 9 out of 63 spout1 knockout zebrafishes (P = 0.009). Transcriptome sequencing revealed 21 differentially expressed genes between spout1 knockout and control groups, including 13 up-regulated and 8 down-regulated genes. Two axonal transport-related genes, kif3a and ap3d1, were most prominently involved in enriched Gene Ontology (GO) terms.

Conclusions: This study identified SPOUT1 as a novel candidate gene of DEE, which follows the autosomal-recessive inheritance pattern. IESS is the most common epilepsy syndrome. Downregulation of axonal transport-related genes, KIF3A and AP3D1, may play a crucial role in the pathogenesis of DEE.