Abundant pleiotropy across neuroimaging modalities identified through a multivariate genome-wide association study

Genetic pleiotropy is abundant across spatially distributed brain characteristics derived from one neuroimaging modality (e.g. structural, functional or diffusion magnetic resonance imaging [MRI]). A better understanding of pleiotropy across modalities could inform us on the integration of brain function, micro- and macrostructure. Here we show extensive genetic overlap across neuroimaging modalities at a locus and gene level in the UK Biobank (N = 34,029) and ABCD Study (N = 8607). When jointly analysing phenotypes derived from structural, functional and diffusion MRI in a genome-wide association study (GWAS) with the Multivariate Omnibus Statistical Test (MOSTest), we boost the discovery of loci and genes beyond previously identified effects for each modality individually. Cross-modality genes are involved in fundamental biological processes and predominantly expressed during prenatal brain development. We additionally boost prediction of psychiatric disorders by conditioning independent GWAS on our multimodal multivariate GWAS. These findings shed light on the shared genetic mechanisms underlying variation in brain morphology, functional connectivity, and tissue composition.

[Genetics of brain networks]

BACKGROUND

Genetic analyses reveal multiple genes and pathways that are involved in brain networks. Similarly, for psychiatric disorders several genes and reliable changes in brain features have been found, raising the question of the relationship between the two.

AIM

To explore the genetics of brain networks in relation to mental health.

METHOD

Review of selected literature on the genetics of brain networks in the context of common psychiatric phenotypes.

RESULTS

Well-defined genetic conditions allow us to infer the relationship between brain networks and symptoms. In complex traits where many genes have an effect, genome-wide association studies can help us interrogate their genetics.

CONCLUSION

The combination of neuroimaging and genetics data opens new possibilities to map the biological processes that underpin behaviour, mental health and psychiatric conditions.

Connectome organization is related to longitudinal changes in general functioning, symptoms and IQ in chronic schizophrenia

Emerging evidence suggests schizophrenia to involve widespread alterations in the macroscale wiring architecture of the human connectome. Recent findings of attenuated connectome alterations in unaffected siblings of schizophrenia patients suggest that altered connectome organization may relate to the vulnerability to develop the disorder, but whether it relates to progression of illness after disease onset is currently unknown. Here, we examined the interaction between connectome structure and longitudinal changes in general functioning, clinical symptoms and IQ in the 3years following MRI assessment in a group of chronically ill schizophrenia patients. Effects in patients were compared to associations between connectome organization and changes in subclinical symptoms and IQ in healthy controls and unaffected siblings of schizophrenia patients. Analyzing the patient sample revealed a relationship between structural connectivity-particularly among central 'brain hubs'-and progressive changes in general functioning (p=0.007), suggesting that more prominent impairments of hub connectivity may herald future functional decline. Our findings further indicate that affected local connectome organization relates to longitudinal increases in overall PANSS symptoms (p=0.013) and decreases in total IQ (p=0.003), independent of baseline symptoms and IQ. No significant associations were observed in controls and siblings, suggesting that the findings in patients represent effects of ongoing illness, as opposed to normal time-related changes. In all, our findings suggest connectome structure to have predictive value for the course of illness in schizophrenia.

Smaller hippocampal volume as a vulnerability factor for the persistence of post-traumatic stress disorder

BACKGROUND

Smaller hippocampal volume has often been observed in patients with post-traumatic stress disorder (PTSD). However, there is no consensus whether this is a result of stress/trauma exposure, or constitutes a vulnerability factor for the development of PTSD. Second, it is unclear whether hippocampal volume normalizes with successful treatment of PTSD, or whether a smaller hippocampus is a risk factor for the persistence of PTSD.

METHOD

Magnetic resonance imaging (MRI) scans and clinical interviews were collected from 47 war veterans with PTSD, 25 healthy war veterans (combat controls) and 25 healthy non-military controls. All veterans were scanned a second time with a 6- to 8-month interval, during which PTSD patients received trauma-focused therapy. Based on post-treatment PTSD symptoms, patients were divided into a PTSD group who was in remission (n = 22) and a group in whom PTSD symptoms persisted (n = 22). MRI data were analysed with Freesurfer.

RESULTS

Smaller left hippocampal volume was observed in PTSD patients compared with both control groups. Hippocampal volume of the combat controls did not differ from healthy controls. Second, pre- and post-treatment analyses of the PTSD patients and combat controls revealed reduced (left) hippocampal volume only in the persistent patients at both time points. Importantly, hippocampal volume did not change with treatment.

CONCLUSIONS

Our findings suggest that a smaller (left) hippocampus is not the result of stress/trauma exposure. Furthermore, hippocampal volume does not increase with successful treatment. Instead, we demonstrate for the first time that a smaller (left) hippocampus constitutes a risk factor for the persistence of PTSD.

Graph analysis of the anatomical network organization of the hippocampal formation and parahippocampal region in the rat

Graph theory was used to analyze the anatomical network of the rat hippocampal formation and the parahippocampal region (van Strien et al., Nat Rev Neurosci 10(4):272-282, 2009). For this analysis, the full network was decomposed along the three anatomical axes, resulting in three networks that describe the connectivity within the rostrocaudal, dorsoventral and laminar dimensions. The rostrocaudal network had a connection density of 12% and a path length of 2.4. The dorsoventral network had a high cluster coefficient (0.53), a relatively high path length (1.62) and a rich club was identified. The modularity analysis revealed three modules in the dorsoventral network. The laminar network contained most information. The laminar dimension revealed a network with high clustering coefficient (0.47), a relatively high path length (2.11) and four significantly increased characteristic network building blocks (structural motifs). Thirteen rich club nodes were identified, almost all of them situated in the parahippocampal region. Six connector hubs were detected and all of them were located in the entorhinal cortex. Three large modules were revealed, indicating a close relationship between the perirhinal and postrhinal cortex as well as between the lateral and medial entorhinal cortex. These results confirmed the central position of the entorhinal cortex in the (para)hippocampal network and this possibly explains why pathology in this region has such profound impact on cognitive function, as seen in several brain diseases. The results also have implications for the idea of strict separation of the "spatial" and the "non-spatial" information stream into the hippocampus. This two-stream memory model suggests that the information influx from, respectively, the postrhinal-medial entorhinal cortex and the perirhinal-lateral entorhinal cortex is separate, but the current analysis shows that this apparent separation is not determined by anatomical constraints.

Effects of aging on BOLD fMRI during prosaccades and antisaccades

Age affects the ability to inhibit saccadic eye movements. According to current theories, this may be associated with age-induced neurophysiological changes in the brain and with compensatory activation in frontal brain areas. In the present study, the effects of aging are assessed on brain systems that subserve generation and inhibition of saccadic eye movements. For this purpose, an event-related functional magnetic resonance imaging design was used in adults covering three age ranges (18-30, 30-55, and 55-72 years). Group differences were controlled for task performance. Activity associated with saccadic inhibition was represented by the contrast between prosaccade and antisaccade activation. The tasks activated well-documented networks of regions known to be involved in generation and inhibition of saccadic eye movements. There was an age-related shift in activity from posterior to frontal brain regions after young adulthood. In addition, old adults demonstrated an overall reduction in the blood oxygenation level dependent (BOLD) signal in the visual and oculomotor system. Age, however, did not affect saccade inhibition activity. Mid and old adults appear to increase frontal activation to maintain performance even during simple prosaccades. The global reduction of the BOLD response in old adults could reflect a reduction in neural activity, as well as changes in the neuronal-vascular coupling. Future research should address the impact of altered vascular dynamics on neural activation and the BOLD signal.

Identification and quantification of intermediates of unsaturated fatty acid metabolism in plasma of patients with fatty acid oxidation disorders

The free fatty acid and total fatty acid profiles in plasma of nine patients with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, two with very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency and two with mild-type multiple acyl-CoA dehydrogenase (MAD-m) deficiency, were analyzed by gas chromatography-mass spectrometry. In the plasma of patients with MCAD deficiency we found increases of octanoic acid (8:0), decanoic acid (10:0), 4-decenoic acid (10:1 omega 6), and 4,7-decadienoic acid (10:2 omega 3), all present almost exclusively in free form. The patients with VLCAD deficiency showed increases of mainly 5-tetradecenoic acid (14:1 omega 9) and to a minor extent 5-dodecenoic acid (12:1 omega 7), 5,8-tetradecadienoic acid (14:2 omega 6), and 7,10-hexadecadienoic acid (16:2 omega 6), in both the free and esterified fatty acid fraction. The MAD-m patients showed variable increases of all the unusual fatty acids present in MCAD- and VLCAD-deficient plasma. The 14:1 omega 9, 14:2 omega 6, and 16:2 omega 6 fatty acids were present mainly in the esterified form. Measurement of these fatty acids in plasma by the relatively simple method presented here provides a sensitive and specific aid in the diagnosis of acyl-CoA dehydrogenase deficiency disorders.

Identification and quantification of intermediates of unsaturated fatty acid metabolism in plasma of patients with fatty acid oxidation disorders

The free fatty acid and total fatty acid profiles in plasma of nine patients with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, two with very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency and two with mild-type multiple acyl-CoA dehydrogenase (MAD-m) deficiency, were analyzed by gas chromatography-mass spectrometry. In the plasma of patients with MCAD deficiency we found increases of octanoic acid (8:0), decanoic acid (10:0), 4-decenoic acid (10:1 omega 6), and 4,7-decadienoic acid (10:2 omega 3), all present almost exclusively in free form. The patients with VLCAD deficiency showed increases of mainly 5-tetradecenoic acid (14:1 omega 9) and to a minor extent 5-dodecenoic acid (12:1 omega 7), 5,8-tetradecadienoic acid (14:2 omega 6), and 7,10-hexadecadienoic acid (16:2 omega 6), in both the free and esterified fatty acid fraction. The MAD-m patients showed variable increases of all the unusual fatty acids present in MCAD- and VLCAD-deficient plasma. The 14:1 omega 9, 14:2 omega 6, and 16:2 omega 6 fatty acids were present mainly in the esterified form. Measurement of these fatty acids in plasma by the relatively simple method presented here provides a sensitive and specific aid in the diagnosis of acyl-CoA dehydrogenase deficiency disorders.

Improved determination of very-long-chain fatty acids in plasma and cultured skin fibroblasts: applications to the diagnosis of peroxisomal disorders

Current techniques for the determination of very-long-chain fatty acids from biological samples require laborious procedures including solvent extraction of lipids, purification, hydrolysis, derivatization, purification of derivatized fatty acids by thin-layer chromatography and finally gas chromatographic analysis. A comparison was made between such a procedure based on solvent extraction and a method based on a recently developed direct one-step transesterification reaction. The latter method proved to be much faster and led to higher recoveries of all individual very-long-chain fatty acids from both plasma and skin fibroblasts. The assay proved to be very convenient in the diagnosis of genetically determined disorders in which very-long-chain fatty acids accumulate in tissues and body fluids. Because of its simplicity and speed and because it can be performed with as little as 100 microliters of plasma, the method can be recommended as a valuable screening procedure for peroxisomal disorders.