Tolerability and Efficacy of L-Serine in Patients With GRIN-related Encephalopathy

GRIN-related disorders encompass a new group of Inborn Errors of Metabolism according to the recent nosology published by Ferreira et al (Genet Med, 2019). These rare conditions represent a subtype of paediatric encephalopathies leading to intellectual disability, hypotonia, communication deficits and motor impairment (Orphanet entries: 178469, 289266, 101685, for GRIN1, GRIN2A and GRIN2B, respectively). Mutations leading to glutamatergic hypotransmission can be potentially treated with L-Serine leading to significant clinical benefits in patients according to a pilot study published by our group (Soto et al, 2019). In our study, the investigators will include about 20 spanish patients older than 2 years of age, harbouring GRIN variants functionally anotated as loss-of-function pathogenic variants. The investigators will evaluate dose tolerability, efficacy of the treatment according to neurocognitive and motor scales, as well as the effects of L-serine in microbiome composition.