Hippocampal glutamate-glutamine (Glx) in adults with Down syndrome: a preliminary study using in vivo proton magnetic resonance spectroscopy ((1)H MRS).
BACKGROUND
Down syndrome (DS), or trisomy 21, is one of the most common autosomal mutations. People with DS have intellectual disability (ID) and are at significantly increased risk of developing Alzheimer's disease (AD). The biological associates of both ID and AD in DS are poorly understood, but glutamate has been proposed to play a key role. In non-DS populations, glutamate is essential to learning and memory and glutamate-mediated excitotoxicity has been implicated in AD. However, the concentration of hippocampal glutamate in DS individuals with and without dementia has not previously been directly investigated. Proton magnetic resonance spectroscopy ((1)H MRS) can be used to measure in vivo the concentrations of glutamate-glutamine (Glx). The objective of the current study was to examine the hippocampal Glx concentration in non-demented DS (DS-) and demented DS (DS+) individuals.


METHODS
We examined 46 adults with DS (35 without dementia and 11 with dementia) and 39 healthy controls (HC) using (1)H MRS and measured their hippocampal Glx concentrations.


RESULTS
There was no significant difference in the hippocampal Glx concentration between DS+ and DS-, or between either of the DS groups and the healthy controls. Also, within DS, there was no significant correlation between hippocampal Glx concentration and measures of overall cognitive ability. Last, a sample size calculation based on the effect sizes from this study showed that it would have required 6,257 participants to provide 80% power to detect a significant difference between the groups which would indicate that there is a very low likelihood of a type 2 error accounting for the findings in this study.


CONCLUSIONS
Individuals with DS do not have clinically detectable differences in hippocampal Glx concentration. Other pathophysiological processes likely account for ID and AD in people with DS.
Sackler Institute for Translational Neurodevelopment, Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King's College London, London, UK ; Southern Health NHS Foundation Trust, North Hampshire Community Learning Disability Service, Winchester, Hampshire UK.
Giles My
GM
Tan
Sackler Institute for Translational Neurodevelopment, Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King's College London, London, UK.
Felix
F
Beacher
Sackler Institute for Translational Neurodevelopment, Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King's College London, London, UK.
Eileen
E
Daly
Sackler Institute for Translational Neurodevelopment, Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King's College London, London, UK.
Jamie
J
Horder
Greenfields Monyhull Hospital, Kings Norton, Birmingham UK.
Verinder
V
Prasher
Northumberland Tyne and Wear NHS Foundation Trust, Northgate Hospital, Morpeth, Northumberland UK.
Maria-Luisa
ML
Hanney
Department of Psychology, Institute of Psychiatry, King's College London, London, UK.
Robin
R
Morris
Department of Old Age Psychiatry, Institute of Psychiatry, King's College London, London, UK.
Simon
S
Lovestone
Department of Psychiatry, Royal College of Surgeons in Ireland, Dublin, Ireland.
Kieran C
KC
Murphy
Department of Neuroimaging, Institute of Psychiatry, King's College London, London, UK ; NIHR Biomedical Research Centre for Mental Health and Biomedical Research Unit for Dementia, South London and Maudsley NHS Foundation Trust, London, UK.
Andrew
A
Simmons
Sackler Institute for Translational Neurodevelopment, Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King's College London, London, UK ; NIHR Biomedical Research Centre for Mental Health and Biomedical Research Unit for Dementia, South London and Maudsley NHS Foundation Trust, London, UK.
Declan Gm
DG
Murphy
1H MRS; Alzheimer’s disease; Dementia; Down syndrome; Glutamate-glutamine (Glx); Hippocampus; Intellectual disability; Magnetic resonance spectroscopy