Metabolic Signatures Differentiate Rett Syndrome From Unaffected Siblings

Abstract

Rett syndrome (RTT, OMIM 312750), a severe neurodevelopmental disorder characterized by regression with loss of spoken language and hand skills, development of characteristic hand stereotypies, and gait dysfunction, is primarily caused by de novo mutations in the X-linked gene Methyl-CpG-binding protein 2 (MECP2). Currently, treatment options are limited to symptomatic management, however, reversal of disease phenotype is possible in mouse models by restoration of normal MECP2 gene expression. A significant challenge is the lack of biomarkers of disease state, disease severity, or treatment response. Using a non-targeted metabolomic approach we evaluated metabolite profiles in plasma from thirty-four people with RTT compared to thirty-seven unaffected age-and gender-matched siblings. We identified sixty-six significantly altered metabolites that cluster broadly into amino acid, nitrogen handling, and exogenous substance pathways. RTT disease metabolite and metabolic pathways abnormalities point to evidence of oxidative stress, mitochondrial dysfunction, and alterations in gut microflora. These observed changes provide insight into underlying pathological mechanisms and the foundation for biomarker discovery of disease severity biomarkers.

Metabolomic Fingerprint of Mecp2-Deficient Mouse Cortex: Evidence for a Pronounced Multi-Facetted Metabolic Component in Rett Syndrome

“…Previous studies of brain metabolite alterations in postmortem patient tissue samples or of Mecp2 -mutant mice were ad hoc and targeted to a specific group of molecules, mainly neurotransmitters and their breakdown products (see below). Only one untargeted metabolome study has been conducted to date, focusing on the blood plasma of RTT patients and control subjects [ 37 ]. It must be considered that we studied the most severe conditions arising in the adult male, hemizygous Mecp2 −/y mouse model.…”

“…However, these concomitant changes could not be observed in CSF [ 62 ]. A more recent study revealed in RTT patient-derived blood samples clear changes in amino acid levels, with an increase or trending increase in aspartate, glutamate, cysteine, glycine, and serine, and a decrease or trending decrease in arginine, histidine, and phenylalanine [ 37 ]. In contrast, an RTT mouse study on full brain extracts yielded only slight changes in amino acid levels (glutamine increased, GABA trend to decrease).…”

“…Thirteen of the 20 proteinogenic amino acids (L-alanine, L-glutamic acid, L-leucine, L-isoleucine, L-lysine, L-methionine, L-phenylalanine, L-proline, L-serine, L-threonine, L-tryptophan, L-tyrosine, and L-valine) showed significantly elevated concentrations in the Mecp2 −/y cortex (see also Table 1 , Figure 4 ). A metabolomics study of RTT patient’s plasma revealed significant changes in four proteinogenic amino acids: aspartate and glutamate were upregulated, whereas arginine and histidine were downregulated [ 37 ]. In our study, only one of the four, L-glutamic acid, was detected as being significantly upregulated.…”

“…From the mechanistic perspective, liver failure should be considered as a cause of the increased urea levels in the Mecp2 −/y cortex, because Mecp2 deletion in mice also results in a fatty liver [ 79 ]. It should be mentioned, however, that urea levels did not differ in the plasma of RTT patients and control subjects (see [ 37 ], Supplementary Materials Table S3 of this reference).…”

“…Metabolomic studies in RTT are currently in their early stages but bear the potential to provide global insights into pathogenic mechanisms. Recently, the suitability of this approach was demonstrated in a first metabolomics study on RTT patient-derived blood samples [ 37 ], and the characterization of the gut microbiome and metabolome in RTT patients [ 38 ]. An earlier pilot metabolic screening in male Mecp2 -null ( Mecp2 −/y ) mice analyzed full brain extracts by means of high-resolution magnetic resonance spectroscopy.…”