Targeting the Diagnosis in an Adolescent with Epilepsy and Intellectual Disability through Next-Generation Metabolic Screening

A 16-year-old boy, born to consanguineous parents in Syria and living as a refugee in the Netherlands since the age of 14 years, was admitted to our tertiary pediatric intensive care unit with status epilepticus after discontinuation of valproic acid. He was treated with valproic acid since early infancy for seizures of unknown cause, but as he had been seizure-free for many years, discontinuation was attempted. Brain magnetic resonance imaging showed nonspecific white matter abnormalities and changes attributable to prolonged seizures or meningitis, such as brain fullness with mildly effaced ventricles and mild meningeal enhancement in the precentral gyri. Chromosomal microarray analysis showed a normal XY profile. Biochemical screening for inherited metabolic disorders (IMD) was performed through next-generation metabolic screening (NGMS) (1), an ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry (Agilent 6545 QTOF) metabolomics approach, validated under ISO15189 accreditation as first-tier diagnostic screening for IMD in our laboratory. In short, a panel of known IMD-related metabolites is filtered from the untargeted metabolomics data for initial diagnostic interpretation. For each patient, significantly altered metabolites are identified, and a semiquantitative fold change compared to controls is evaluated. The NGMS IMD-metabolite panel is frequently updated to include novel diagnostic metabolites encountered in the untargeted metabolomics data in a research setting. For example, the metabolites 2S, 6S- and 2S; 6R-oxopropylpiperidine-2-carboxylic acid; 6-oxopiperidine-2-carboxylic acid; and 6-(carboxymethyl)piperidine-2-carboxylic acid were recently added to the panel as novel biomarkers for pyridoxine dependent epilepsy due to deficiency of α-aminoadipic semialdehyde dehydrogenase, encoded by ALDH7A1 (PDE-ALDH7A1) (2, 3). PDE-ALDH7A1 is a defect in lysine catabolism (Fig. 1), leading to secondary deficiency of pyridoxine (vitamin B6) through complexation with accumulating piperideine-6-carboxylic acid.