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The brain-derived neurotrophic factor Val66Met variant is associated with hippocampal volumes in newborn infants1Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States, 2Division of Neonatology, Maternal and Perinatal Center, Toyama University Hospital, Toyama, Japan, 3University of Hawaii, Honolulu, HI, United States, 4Key Laboratory for Biomedical Engineering of Ministry of Education, College of Biomedical Engineering & Instrument Science, Zhejiang University, Hangzhou, China, 5Department of Neurology, Kobe University, Kobe, Japan, 6Center for Imaging Science Faculty, Johns Hopkins University, Baltimore, MD, United States, 7Diagnostic Radiology and Nuclear Medicine, and Neurology, University of Maryland, Baltimore, MD, United States, 8Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, United States
Synopsis
The brain-derived neurotrophic factor (BDNF) Val66Met variant (Met+) is associated
with onset of neuropsychiatric disorders. Met+ individuals had smaller hippocampi than
those with Met-; whether this phenotype is present at birth is unknown. To
minimize postnatal environmental influences, we studied newborn Met+ and Met-
infants and compared their hippocampal volumes relative to the intracranial
volumes (ICV). Hippocampal volumes and ICVs were automatically parcellated. The Met+ group had significantly smaller %
hippocampal volumes than the Met- group (p=0.011). The BDNF Val66Met
variant is associated with smaller hippocampal volumes in newborn infants,
suggesting the gene’s effects on prenatal
hippocampal development.
INTRODUCTION:
A common and functionally relevant single nucleotide polymorphism for the brain-derived neurotrophic factor (BDNF), the Val66Met variant, with a methionine substitution for valine at residue 66 (Met+), has been associated with poorer learning and memory1-4 and onset of neuropsychiatric disorders.5 Human subjects with the Met+ allele also showed abnormal hippocampal activation on functional MRI, and lower hippocampal N-acetyl aspartate (NAA) on MR spectroscopy.4 Furthermore, Met+ adults and adolescents had smaller hippocampi compared to those without the substitution (Met-), although the results are still controversial and whether the smaller hippocampi resulted from other postnatal environmental influences is unknown. These inconsistencies may be attributed to the complex role that BNDF might have, including gene-gene interactions and epigenetic or environmental influences, which ultimately may influence hippocampal development or remodeling.6 To minimize postnatal environmental influences, we studied newborn infants and compared the hippocampal volumes of those with and without the BNDF Val66Met variant.METHODS:
Participants: 66 healthy newborn infants (36 boys and 30 girls) underwent an MRI scan at 37.9 – 47.6 postmenstrual weeks and were evaluated for the BDNF genotype. The participants were part of a larger neuro-development study, which was approved by the Cooperative IRB of the Queen's Medical Center, the University of Hawaii, and the Johns Hopkins University.
BDNF genotyping: Buccal swabs were obtained from these infants. Genotyping for BDNF rs6265 was done using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) followed by electrophoresis on a 4% agarose gel. AflIII restriction enzyme was used resulting in 2 bands of 77 and 59-bp for the G allele and 2 bands of 143- and 59-bp for the A allele.
MRI acquisition: All MRI scans were performed at the University of Hawaii and the Queen's Medical Center MR Research Center in Honolulu, HI, as described in our prior work.7,8A 3D magnetization-prepared rapid gradient echo (MPRAGE) scan was acquired with the following parameters: TE = 4.15 ms, TI = 1400 ms, TR = 3200 ms, flip angle = 7°, matrix 176 x 256 x 160, 1 mm isotropic resolution.
Image analysis: The MRIs were automatically parcellated into hippocampus and intracranial space (Fig. 1) using a multi-atlas label fusion method, implemented in the MRICloud (https://braingps.anatomyworks.org) 9for the volume measurement. The resultant parcellation maps for each MRI were reviewed by a neonatologist for the quality control. The raw hippocampal volume was normalized relative to the intracranial volume (ICV).
Statistics: Effects of the genotypes Met+ (Met/Met or Met/Val) vs. Met- (Val/Val) on the ICV and % hippocampal volume relative to ICV were investigated using analysis of covariance, with postmenstrual age and sex as covariates.
RESULTS:
The Met+ and Met- groups had similar postmenstrual age and sex-proportion. All structural brain MRIs were reviewed visually and found to be normal. The ICVs in the Met+ and Met- groups were not significantly different. However, the average % hippocampal volume relative to the ICV of the Met+ group (0.36%) was significantly smaller than that of the Met- group (0.38%) (ANCOVA-p=0.011) (Fig. 2).DISCUSSION:
Although the hippocampal volumes were assessed in newborn infants that had minimal postnatal environmental influences, the Met+ group demonstrated smaller relative hippocampal volumes than the Met- group. This finding is consistent with findings from animal and in-vitro studies,4,6 as well as findings in some adolescent and adult human studies,10,11 regarding the role of the BDNF Met allele. Our result suggests that the smaller hippocampi represent a prenatal phenotypic expression of the Met+ allele, rather than atrophy due to the postnatal influences. The mechanism of how the BNDF Met allele affects hippocampal development is not fully understood. Mice expressing Val66Met BDNF displayed low level of extracellular BDNF despite the normal level of total BDNF expression and constitutive secretion of BDNF;1 therefore, reduced levels of extracellular BNDF might also have influenced the hippocampal development in our Met+ infants. Further studies are needed to investigate the possible interactive relationships between the BDNF Met allele and other prenatal factors. Met+ is a known risk factor for the onset of neuropsychiatric disorders,5 and smaller hippocampi were commonly reported in those with neuropsychiatric disorders.12 Whether the reduced hippocampal volume also predicts future development of neuropsychiatric disorders is yet to be investigated.CONCLUSION:
The BDNF Val66Met variant is associated with smaller hippocampal volumes in newborn infants, suggesting the gene’s effects on prenatal hippocampal development.Acknowledgements
This publication was made possible by grants from the National Institutes of Health (NIH: R01HD065955; U54NS56883). The contents of this paper are solely the responsibility of the authors and do not necessarily represent the official views of the NIH or the authors’ affiliated institutions. We thank all the families for their willingness to participate in this study. The authors declare no conflicts of interest.References
1. Park H, Poo MM. Neurotrophin regulation of neural circuit development and function. Nat Rev Neurosci. 2013;14(1):7-23
2. H. Frielingsdorf, K.G. Bath, F. Soliman, et al. Variant brain-derived neurotrophic factor Val66Met endophenotypes: implications for posttraumatic stress disorder. Ann. N. Y. Acad. Sci.2010; 1208:150-157 3. C. Cunha, R. Brambilla, K.L. Thomas. A simple role for BDNF in learning and memory? Front. Mol. Neurosci.2010;3:1
4. M.F. Egan, M. Kojima, J.H. Callicott, et al. The BDNF val66met polymorphism affects activity-dependent secretion of BDNF and human memory and hippocampal function. Cell.2003;112: 257-269
5. L. Chen, D.A. Lawlor, S.J. Lewis, et al. Genetic association study of BDNF in depression: Finding from two cohort studies and a meta-analysis. Am. J. Med. Genet.2008;147B:814-821.
6. Magariños AM, Li CJ, Gal Toth J, et al. Effect of brain-derived neurotrophic factor haploinsufficiency on stress-induced remodeling of hippocampal neurons. Hippocampus. 2011;21(3):253-64.
7. Akazawa K, Chang L, Yamakawa R, et al. Probabilistic maps of the white matter tracts with known associated functions on the neonatal brain atlas: Application to evaluate longitudinal developmental trajectories in term-born and preterm-born infants. NeuroImage. 2016; 128: 167-79.
8.Chang L, Oishi K, Skranes J, Buchthal S, Cunningham E, Yamakawa R, Hayama S, Jiang CS, Alicata D, Hernandez A, Cloak C, Wright T, Ernst T. Sex-Specific Alterations of White Matter Developmental Trajectories in Infants With Prenatal Exposure to Methamphetamine and Tobacco. JAMA Psychiatry. 2016 ;73(12):1217-1227.
9. Tang X, Oishi K, Faria AV, et al. Bayesian Parameter Estimation and Segmentation in the Multi-Atlas Random Orbit Model. PloS one. 2013; 8: e65591.
10. Molendijk ML, Bus BA, Spinhoven P, et.al. A systematic review and meta-analysis on the association between BDNF val (66) met and hippocampal volume--a genuine effect or a winners curse? Am J Med Genet B Neuropsychiatr Genet. 2012;159B (6):731-40.
11. Harrisberger F, Spalek K, Smieskova R, et al. The association of the BDNF Val66Met polymorphism and the hippocampal volumes in healthy humans: a joint meta-analysis of published and new data. Neurosci Biobehav Rev. 2014; 42:267-78.
12. Harrisberger F, Smieskova R, Schmidt A, et al. BDNF Val66Met polymorphism and hippocampal volume in neuropsychiatric disorders: A systematic review and meta-analysis. Neurosci Biobehav Rev. 2015; 55:107-18.
13. Otsuka Y, Chang L, Skranes J, Ernst T and Oishi K. Neonatal brain MRI multi-atlas repository for automated image quantification. XXIII World Congress of Neurology. Kyoto, Japan2017.
Figures
A representative MRI of the infant with the parcellation map. The multi-atlas label fusion method implemented in MRICloud was used for the fully automated parcellation.13
(A) Boundaries of the ICV and the hippocampus. Red line shows the contour of the hippocampus and yellow line shows the contour of the ICV.
(B) Magnified view of the hippocampus.
(A) These bargraphs show the average % hippocampal volumes and standard deviations (SD) of the Met+ (orange) and Met- (blue) infants.
(B) These bargraphs show the average ICVs and standard deviations (SD) of the Met+ (orange) and Met- (blue) infants.