PP03.15 – 2755: Clinical metabolomics reveals a novel plasma biomarker for Snyder Robinson syndrome (X-linked spermine synthase deficiency)

Objective Clinical metabolomics has emerged as a powerful tool to study metabolic perturbations in various diseases and to unravel novel biomarkers. In a monocenter study on metabolic-genetic research into epileptic encephalopathies, we applied untargeted metabolomics in parallel with exome sequencing in twin brothers with epileptic encephalopathy of unknown etiology. Genetic analysis confirmed Snyder-Robinson syndrome (SRS), a rare X-linked mental retardation syndrome. The underlying spermine synthase (SMS) deficiency affects polyamine metabolism and reduces intracellular spermine. So far, the diagnosis of SRS relied on a reduced spermine/spermidine ratio in lymphoblasts and/or sequencing of the SMS gene. Case The male monozygotic twins presented with developmental delay, progressive microcephaly and discrete dysmorphic features. From the age of 12 months, they developed therapy-resistant seizures with recurrent irregular myoclonic jerks and serial spasms in twin A. The EEG showed an abnormal background activity and multifocal and generalized spike waves. Additional atonic and tonic seizures and atypical absences occurred in both. At the age of 15 months, they developed a severe encephalopathy with frequent seizures, loss of milestones, impairment of visual interaction and a transient choreo-athetotic movement disorder. Both twins showed signs of osteopenia, twin B suffered a non-traumatic clavicular fraction at 23 months. Methods Clinical exome sequencing was applied in both twins and their parents. Sanger sequencing was applied to confirm the candidate variant. An untargeted plasma metabolomics analysis was performed by liquid chromatography–high-resolution mass spectrometry (LC-MS). Results Exome sequencing revealed a novel SMS missense mutation. Discriminant statistical analysis of the LC-MS data showed a distinct plasma metabolomics profile while comparative analysis versus age-matched controls revealed significantly elevated levels of N-acetylspermidine, a metabolite involved in spermine metabolism. Conclusion A combined clinical “omics” approach revealed N-acetylspermidine as a novel plasma biomarker for spermine synthase deficiency and identified a novel missense mutation in twin boys with SRS.