A CLN8 biallelic missense variant causes epilepsy with severe treatment-resistant psychosis.

Epilepsy and psychosis are dysfunctions of the nervous system that may occasionally co-occur. The current study was designed to investigate the causes of psychosis with or without epilepsy in Pakistani families. We identified two consanguineous families in which all affected members had treatment-resistant psychosis while three patients also had epilepsy. Every participant was examined by psychiatrists and a psychologist, while epilepsy was diagnosed by neurologists. The doctors confirmed the presence of severe psychosis with or without epilepsy in the patients and their absence in other participants. Exome sequencing identified a biallelic variant c.570G > T; p.Trp190Cys in CLN8 that segregated with the phenotype of epilepsy with psychosis in one family whereas the results for the other family were negative. CLN8 variant affects an amino acid which is conserved in diverse vertebrate orthologues. In-silico analysis indicated that substitution of tryptophan with cysteine resulted in the loss of an intramolecular interaction, which may affect protein folding. This study emphasizes that CLN8-related phenotype can include severe treatment-resistant psychosis and also provides a genotypic extension.