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Article

Alteration of Fatty Acid Profile in Fragile X Syndrome

by
Armita Abolghasemi
1,
Maria Paulina Carullo
2,
Ester Cisneros Aguilera
3,
Asma Laroui
1,
Rosalie Plantefeve
1,
Daniela Rojas
1,
Serine Benachenhou
1,
María Victoria Ramírez
2,
Mélodie Proteau-Lemieux
4,
Jean-François Lepage
4,
François Corbin
1,
Mélanie Plourde
3,
Mauricio Farez
2,
Patricia Cogram
5 and
Artuela Çaku
1,*
1
Centre de Recherche du CHUS, Department of Biochemistry, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
2
Department of Child Neurology, Raúl Carrea Institute for Neurological Research (FLENI), Buenos Aires C1428AQK, Argentina
3
Centre de Recherche sur le Vieillissement, Departments of Medicine, University of Sherbrooke, Sherbrooke, QC J1H 4C4, Canada
4
Department of Pediatrics and Centre de Recherche du CHUS, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
5
Biomedicine Division, Centre for Systems Biotechnology, Fraunhofer Chile Research Foundation, Santiago 7500588, Chile
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2022, 23(18), 10815; https://doi.org/10.3390/ijms231810815
Submission received: 9 July 2022 / Revised: 28 August 2022 / Accepted: 12 September 2022 / Published: 16 September 2022
(This article belongs to the Special Issue Emerging Role of Lipids in Metabolism and Disease – 3rd Edition)

Abstract

:
Fragile X Syndrome (FXS) is the most prevalent monogenic cause of Autism Spectrum Disorders (ASDs). Despite a common genetic etiology, the affected individuals display heterogenous metabolic abnormalities including hypocholesterolemia. Although changes in the metabolism of fatty acids (FAs) have been reported in various neuropsychiatric disorders, it has not been explored in humans with FXS. In this study, we investigated the FA profiles of two different groups: (1) an Argentinian group, including FXS individuals and age- and sex-matched controls, and (2) a French-Canadian group, including FXS individuals and their age- and sex-matched controls. Since phospholipid FAs are an indicator of medium-term diet and endogenous metabolism, we quantified the FA profile in plasma phospholipids using gas chromatography. Our results showed significantly lower levels in various plasma FAs including saturated, monosaturated, ω-6 polyunsaturated, and ω-3 polyunsaturated FAs in FXS individuals compared to the controls. A decrease in the EPA/ALA (eicosapentaenoic acid/alpha linoleic acid) ratio and an increase in the DPA/EPA (docosapentaenoic acid/eicosapentaenoic acid) ratio suggest an alteration associated with desaturase and elongase activity, respectively. We conclude that FXS individuals present an abnormal profile of FAs, specifically FAs belonging to the ω-3 family, that might open new avenues of treatment to improve core symptoms of the disorder.

1. Introduction

Fragile X Syndrome (FXS) is an X-linked neurodevelopmental disorder known to be the most prevalent hereditary monogenic cause of Intellectual Disability (ID) and Autism Spectrum Disorders (ASDs) [1,2]. FXS is caused by a mutation of the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene (FMR1 Fragile X Messenger Ribonucleoprotein 1 [Homo Sapiens (Human)]—Gene—NCBI, n.d.), leading to a deficit in the Fragile X Mental Retardation Protein (FMRP) [3]. It is well established that the decrease in expression of FMR1 affects the brain and cognitive functions [4]. However, the ubiquitous expression of FMRP in the body suggests a specific role in other organs [5]. Specifically, preclinical and clinical studies have shown that the lack of FMRP is associated with metabolic alterations, including a decrease in body fat storage as well as a reduction in plasma glucose, glycerol, and cholesterol levels [6,7,8,9].
Lipid content represents more than half of the brain’s dry weight, and fatty acids are among the most crucial lipid molecules that determine the brain’s integrity and function [10]. Fatty acids (FAs) classify into three categories: saturated FAs (SFAs, with no double bonds), monounsaturated FAs (MUFAs, with a single double bond), and polyunsaturated FAs (PUFAs, with ≥2 double bonds). Further, PUFAs, due to the position of their first double bond on methyl terminals, are classified into omega-3 (ω-3) and omega-6 (ω-6) FAs [11]. PUFAs include important structural and functional FAs such as the essential FAs of linolenic acid (ALA, 18:3 ω-3) and linoleic acid (LA, 18:2 ω-6), which are metabolized by elongation and desaturation into eicosapentaenoic acid (EPA, 20:5 ω-3), docosahexaenoic acid (DHA, 22:6 ω-3), and arachidonic acid (AA, 20:4 ω-6) via the elongase and desaturases enzymes [12,13]. Adequate FA intake is important for brain development, perfusion, inflammatory processes, and the synthesis of neuroprotective metabolites [12,14]. Various studies have shown that the lack of ALA has a behavioral impact on both animal and human models.
Changes in the FA profile of various tissues, including plasma, red blood cells, and post-mortem brain, have been reported in various neuropsychiatric disorders such as attention deficit hyperactivity disorder (ADHD), schizophrenia, anxiety disorders, ID, and ASD [15,16,17,18,19]. Specifically, low levels of plasma ALA, LA, EPA, DHA, and AA have been reported in children with autism compared to the controls [20,21]. Moreover, supplementation with FAs, particularly ω-3 FAs, including ALA, EPA, and DHA, has shown improvements in autistic behavioral symptoms [22,23,24]. Despite these findings in autism, a disorder for which FXS is the prototypic model, to the best of our knowledge, the FA profile in FXS individuals has not been studied. The present work aimed to characterize the FA profile of plasma phospholipids in FXS individuals as compared to healthy controls for the first time. Since FXS is the most prevalent hereditary monogenic cause of intellectual ID and ASD, we hypothesized that FXS individuals would show lower levels of plasma FAs compared to controls, which may provide new insights into treatment strategies for FXS.

2. Results

2.1. Study Population Characteristics

The study population included two groups comprising two ethnic cohorts, as shown in Table 1. The majority of the participants were male. All Argentinian FXS individuals had the full FMR1 mutation, while 11% of the French-Canadian cohort were mosaics. There was no statistical difference in age and sex between FXS individuals and controls. The fasting conditions applied to Argentinian and French-Canadian cohorts were 6 and 12 h, respectively.

2.2. FA Profile

FXS participants showed lower levels for all FAs as compared to controls. The statistical significance was reached for the majority of SFAs, MUFAs, and PUFAs, as shown in Table 2. Specifically, significant lower levels were shown in the total amount of MUFA and PUFA families, with more significancy in PUFA (p = 0.0081 and p = 0.0015, respectively), including both ω-3 and ω-6 with, respectively, 22% and 16% lower levels of FAs in FXS compare to controls. Comparable results were obtained when male FXS were compared to male controls (Supplementary Table S1)
Although our results from age-related analysis showed significant differences in FA levels of FXS adults compared to controls (Supplementary Table S2), interestingly children and adolescent cohorts did not show any difference in the level of FAs compared to controls (Supplementary Tables S3 and S4, respectively).

2.2.1. ω-6 FA Profile

All ω-6 FAs were significantly lower in the FXS group compared to the matched controls (Table 2 and Figure 1). LA (C18:2 ω-6) was significantly lower in both cohorts, Argentinians (14%, median in FXS, 389.4 mg/L, vs. controls, 451.7 mg/L, p = 0.0246) and French-Canadians (39%, median in FXS, 307.6 mg/L, vs. controls, 400.6 mg/L, p = 0.0030) compared to the controls, as shown in Supplementary Tables S5 and S6.

2.2.2. ω-3 FA Profile

There was a decreasing trend for all four measured ω-3 FAs, including ALA (C18:3 ω-3), EPA (C20:5 ω-3), DPA (C22:5 ω-3), and DHA (C22:6 ω-3), as shown in Table 1 and Figure 2. The EPA was lower in both the FXS cohorts of Argentinians (31%, median in FXS, 4.8 mg/L, vs. controls, 9.8 mg/L) and French-Canadians (50%, median in FXS, 10.2 mg/L, vs. controls, 14.5 mg/L) compared to the controls, as shown in Supplementary Tables S5 and S6. Moreover, the DHA was lower in both FXS cohorts, Argentinians (19%, median in FXS, 47.6 mg/L, vs. controls, 58.1 mg/L) and French-Canadians (51%, median in FXS, 39.5 mg/L, vs. controls, 80.8 mg/L) compared to the controls, as shown in Supplementary Tables S5 and S6.

2.3. Estimation of Metabolical Enzymes Activity

The ratio of specific FAs was used to estimate the activity of enzymes involved in FA metabolism. There was a significant decrease in the EPA/ALA (20:5/18:3 ω-3; estimation of delta5 and delta6 desaturase activity) ratio in the FXS group as compared to the controls (medians, respectively, 2.4 vs. 3.1, p = 0.0410). Likewise, there was an increase in the DPA/EPA (22:5/20:5 ω-3; estimation of elongase activity) ratio in the FXS group as compared to the controls (medians, respectively, 2.5 vs. 1.6, p = 0.0455). There was no difference in the ratios of either the 20:4/20:3 or 20:3/18:3 ω-6 FA biosynthesis pathways.

3. Discussion

The metabolic basis of FXS pathology and its impacts on the clinical phenotype are poorly understood. In this study, we performed FA profiling in two distinct cohorts to explore if alterations of FAs reported in ASD are similarly found in FXS. To the best of our knowledge, this report is the first to measure FAs content in plasma phospholipids in humans with FXS as compared to age and sex matched controls.
Our results show a decreasing trend of all measured FAs in FXS as compared to controls, reaching the statistical significance for the majority of SFA, MUFAs, and PUFAs. FAs are involved in the biosynthesis of different lipid structures including sterols, phospholipids, eicosanoids, and glycolipids [25]. We have previously reported lower plasma cholesterol levels in FXS individuals as compared to healthy controls [7]. Taken together, our findings suggest a reduction in all plasma lipids in FXS. Since both FAs and cholesterol are the most abundant lipids in the human brain [26] and are essential for cell membrane integrity and synaptic development [27,28], a reduction in plasma lipid content might have an impact on membrane cell structure and stability. We recently showed that FXS individuals display a reduction in cholesterol content in platelet-derived lipid rafts that were associated with specific traits of aberrant behavior [29]. Indeed, lipid rafts are dynamic structures enriched in lipids that recruit important synaptic receptors (mGluRs, NMDAR, and AMPAR) and facilitate protein–protein and protein-lipid interactions of intracellular signaling molecules [30]. Since platelets are used as a proxy model of human neurons, further lipidomic studies are warranted to explore if FAs are decreased as well. We thus hypothesize that the decrease in total lipids in FXS might have a mechanistic implication in FXS pathophysiology through an alteration of lipid raft content. Specifically, our results showed a significantly lower level of PUFAs, including EPA and DHA in FXS individuals as compared to controls. Consistent with our results, a study on 153 autistic children showed a marked reduction in DHA (22:6 ω-3) levels in plasma phospholipids [31]. Another study on plasma phospholipid fatty acids of 15 ASD children showed lower levels of DHA as compared to 18 children with Intellectual Disability, which resulted in lower levels of total ω-3 and, consequently, a 25% decrease in the ω-3/ω-6 ratio [32]. Comparable results were also reported in ADHD, another disorder for which the phenotype partly overlaps with that of FXS. Specifically, the phospholipid analysis of erythrocytes showed significantly lower levels of DHA and total ω-3; a higher level of total ω-6 and a lower ratio of ω-3/ω-6 FAs in 11 ADHD patients compared to 12 healthy controls [33]. Considering the high prevalence of ASD and ADHD in FXS (respectively, up to 50% and 59%), the consistent findings of FA profile alterations suggest that ω-3 FAs are potentially involved in FXS pathophysiology [34,35]. Indeed, preclinical studies in FXS showed that the supplementation of ω-3 FAs rescued some aspects of Fragile X phenotypes in fmr1-KO mice and rats [36,37]. Specifically, the ω-3 FA supplementation of fmr1-KO mice with a PUFA-enriched diet, containing 11.2% of EPA and 6.5% of DHA, improved their behavioral abnormalities, including alterations in emotionality, social interaction, and non-spatial memory [36]. Moreover, the impact of ω-3 PUFA dietary supplementation was recently investigated on the altered behavior of Fmr1-Δexon 8 rats, another FXS animal model associated with FXS [37]. Their deficits in the social and cognitive domains were counteracted by perinatal ω-3 PUFA supplementation. To the best of our knowledge, there has been no clinical study of FA supplementation on FXS humans, while clinical trials in ASD and ADHD are numerous and advocate that ω-3 supplementation might improve their behavioral phenotype. For instance, early studies in ASD showed that ω-3 FA supplementation with 0.93 g of EPA and DHA for 6 weeks [38] or with 135 mg EPA and 90 mg DHA for 3 months [39] had therapeutic effects on the language and maladaptive behaviors in ASD children. Another open-label study of EPA and DHA supplementation (190 mg of EPA acid and 90 mg of DHA per 500 mg capsule; 2 capsules per day) on ten ASD children showed an improvement on the Autism Treatment Evaluation Checklist [40]. However, a recent double-blind, randomized placebo-controlled study on 54 ASD children showed that supplementation for 6 months with ω-3 FAs (including 800 mg/day of DHA and 25 mg/day of EPA) had no impact on clinical test scores [41].
Meanwhile, a double-blind randomized placebo-controlled trial with 40 boys with ADHD and 39 matched healthy controls showed that daily ω-3 supplementation with 650 mg of EPA and 650 mg of DHA reduced ADHD symptoms after 4 months of treatment [42]. Another double-blind placebo-controlled study of ω-3 FA supplementation with 600 mg EPA and 120 mg DHA for 16 months improved the working memory function in 55 ADHD children [43]. The studies on ASD and ADHD suggest that various ratios of EPA to DHA in ω-3 FA supplements have inconsistent effects on the clinical profile [41,43,44]. DHA and EPA are structural components of cell membranes in the central nervous system. DHA contributes to neuronal growth and differentiation, while EPA has important anti-inflammatory functions [45,46]. Considering the important roles of both these FAs as well as the fact that the majority content of EPA can be converted into DHA [47], we hypothesize that a supplementation formula with a higher EPA content than DHA might be more effective in the treatment of neurodevelopmental disorders, including FXS.
In the current study, we also reported a significant decrease in LA for both cohorts. ALA showed a decreasing trend in FXS individuals as compared to healthy controls, although it did not reach statistical significance. In parallel to our result, two studies in ASD children showed a significant decrease in free plasma LA and ALA as compared to healthy controls [31,48]. The conversion of LA and ALA into their relevant PUFA products is mediated by elongases and desaturases. Specifically, delta5-desaturase and delta6-desaturase are key enzymes of PUFA desaturation [49,50,51]. The two enzymes are very competitive between the ω-6 and ω-3 families, including LA and ALA, as well as their downstream PUFA metabolites such as AA, EPA, and DHA [52]. In the present study, we observed a significant decrease in the EPA/ALA ratio and a significant increase in the DPA/EPA ratio in FXS patients as compared to controls. No significant differences were seen for the ω-6 ratios, suggesting that both desaturases and elongase might be more engaged with ω-6 than ω-3 metabolism. Considering that dietary FA intake along with desaturases determines PUFA quality and quantity [53], further research including food questionnaires and an RNA expression analysis are needed to explore a potential alteration of these enzymes’ activity.
The results of the current study should be considered in light of some limitations. The effects of several factors on the FA profile such as sex, diet, and BMI were not monitored in this study. Since FXS is highly prevalent in males, the limited number of recruited females did not allow us to draw female-related conclusions. Considering difficulties in overseeing the adequate intake of ω-6 and ω-3 through food questionnaires [54], it is not clear if dietary records would have been relevant in the FXS population. In the present study, we quantified FAs in plasma phospholipids, which reflect the dietary intakes during the past few weeks and are not influenced by recent FA intake [55,56]. Moreover, our subgroup analysis showed a significant decrease in DHA and EPA only in adults with FXS. However, the small sample size of children and adolescent participants provides inconclusive results for these age groups. Further studies including young children are warranted to characterize the FA profile abnormalities and, thus, to determine if there is an age range for early intervention in terms of FA supplementation that could benefit this population. In addition, we did not include any data about the clinical profile. For both cohorts, the available clinical data including behavioral questionnaires were inconsistent and insufficient to perform a correlation analysis. Considering the positive results of preclinical studies in FXS and clinical studies in the ASD of PUFA supplementation, we support the inclusion of phenotype evaluations for future studies targeting FA profiles. The identification of clinical traits related to specific PUFAs will help identify potential outcomes for future trials with FA supplementation. Since FXS is a rare disease, it is difficult to recruit and reach a large sample size, although multi-centric studies can help to perform larger scale population studies to validate our results.
In conclusion, the consistent findings in both the Argentinian and Canadian cohorts suggest a perturbation of the FA profile of FXS individuals, in particular of various FAs belonging to the ω-3 family. These observations are somehow consistent with the previous studies on other neurodevelopmental disorders including ASD or ADHD. Our results provide new directions for preclinical research to explore the underlying causes and effects of low plasma lipids in FXS and further explore treatment strategies, including supplementation with EPA and/or DHA.

4. Materials and Methods

4.1. Study Population

The study population included two groups: (1) the FXS group including 23 Argentinian FXS patients and 11 French-Canadians FXS individuals recruited at the Neurology Department of FLENI hospital (Buenos Aires, Argentina) and the Fragile X Clinic of the CIUSS de l’Estrie-CHUS (Sherbrooke, QC, Canada), respectively; (2) the control group including age- and sex-matched healthy individuals, recruited through Neurology Department of FLENI hospital (Buenos Aires, Argentina) and the general population of Sherbrooke (Quebec, Canada).
For the Argentinian FXS cohort, the inclusion criteria comprised (1) males and females older than 4 years of age; (2) a diagnosis of Fragile X Syndrome with molecular genetic confirmation; (3) the ability to undergo a blood draw without sedation or anesthesia; (4) an authorized legal representative (usually father, mother or guardian) having a level of comprehension that allows them to understand the study and its procedures and to thus sign an informed consent form; and (5) permitted concomitant medication being stabilized for at least 4 weeks prior to the blood draw. We excluded the individuals who (1) were treated with dopaminergic drugs, N-methyl-D-aspartate (NMDA) antagonists, tricyclic antidepressants, typical antipsychotics, and/or lithium; (2) have been treated with an experimental drug within the four weeks prior to signing the informed consent form or who are receiving treatment with an experimental drug; (3) have a personal history of cerebrovascular disease, brain trauma, significant endocrine disorders, cancer and/or depressive disorder; (4) have a current drug abuse or dependency disorder or in the three months prior to recruitment; and (5) have significant clinical abnormalities in routine laboratory tests.
For the French-Canadian FXS cohort, the inclusion criteria comprised (1) being male aged from 12 to 50 years old; (2) having a confirmed diagnosis of FXS; and (3) the parent/caregiver being available for the clinic visit and cognitive assessments. For the French-Canadian controls, only the first two criteria were considered. We excluded individuals treated with (1) bleeding diathesis; (2) the use of drugs that affect cholesterol metabolism such as hypolipidemic agents, immunosuppressors, retinoids, and corticosteroids; (3) malignancy; (4) liver or renal dysfunction; (5) uncontrolled hypothyroidism or hyperthyroidism; (6) malabsorption/malnutrition; (7) any acute condition or abnormalities in routine laboratory tests; and (8) any neurological or psychological disorders.
This study was approved by both the Scientific and Ethical Board of the Research Center of Centre Hospitalier Universitaire de Sherbrooke (CHUS) and the Ethical Board of the Neurology Department of FLENI hospital. Written informed consent was obtained from the caregiver/guardian on behalf of the minors and adults with FXS as well as from each participant of the control group.

4.2. Sample Collection

Blood samples were collected in K2EDTA tubes (BD Vacutainer®) for both cohorts. Plasma from the French-Canadian cohort was recovered by centrifugation of the whole blood and then stored at −80 °C until use. In parallel, plasma from the Argentinian cohort was recovered by centrifugation and kept at −80 °C. Plasma samples from Argentina were transported to Canada on dry ice and then transferred to −80 °C until FA analysis.

4.3. FA Extraction and Analysis

For FA quantification, a mixture of the internal standards including 25% of triglycerides (19:0), 25% of cholesteryl esters (17:0), 45.5% of phospholipids (15:0), and 4.5% of the free FAs (24:0) was added to a 200 mL plasma sample. Lipids were extracted using the Folch method [57], evaporated under N2, and then reconstituted in 200 mL chloroform. A solid-phase extraction method was used to separate and extract phospholipids, as previously described [58]. Then, phospholipids were methylated by 12% boron trifluoride methanol solution at 90 °C for 30 min to generate fatty acid methyl esters required for their analysis by gas chromatography (model 6890; Agilent, Palo Alto, CA, USA). Fatty acid methyl esters were separated on a BPX-70 fused capillary column (50 m, SGE, Melbourne, Australia) and detected by a flame ionization detector with the same parameter settings described by Chevalier et al. [59]. The chromatogram analysis was performed using the OpenLab CDS ChemStation. The results were calculated in the absolute concentration of fatty acid methyl esters compared to the internal standard (GLC-569B, Nu-Check Prep, Inc., Elysian, MN, USA).

4.4. Statistical Analysis

Statistical differences between the two groups for age and sex were tested using a t-test or Fisher’s exact test, respectively. Moreover, an age-related analysis was performed on three different age groups of children, adolescents, and adults (presented in the supplementary data). The FA data were not normally distributed; therefore, a non-parametric Mann–Whitney test was used for comparison between the two groups of FXS and controls. Multiple testing correction was performed using the false discovery rate (FDR) [60]. Statistical significance was established at an alpha level of rejection of 0.05. All statistical analyses and graphics were performed in GraphPad Prism (GraphPad Software, Version 9.3.1, San Diego, CA, USA).

5. Conclusions

In conclusion, the consistent findings in both Argentinian and Canadian cohorts suggest a perturbation of FA profiles in FXS individuals, in particular, for various FAs belonging to the ω-3 family. These observations are somehow consistent with previous studies on other neurodevelopmental disorders, including ASD or ADHD. Our results provide new directions for preclinical research to explore the underlying causes and effects of low plasma lipids in FXS and further explore treatment strategies, including supplementation with EPA and/or DHA.

Supplementary Materials

The supporting information can be downloaded at https://www.mdpi.com/article/10.3390/ijms231810815/s1.

Author Contributions

Conceptualization, A.Ç. and P.C.; funding acquisition, P.C. and A.Ç.; supervision, A.Ç.; project administration, A.A., M.P.C. and M.F.; investigation, E.C.A., A.L., D.R. and M.V.R.; formal analysis, S.B. and R.P.; visualization, A.A., P.C. and A.Ç.; validation, M.P.-L., P.C. and R.P.; writing, A.A., M.P.C. and A.Ç.; review and editing, M.P., M.P.-L., J.-F.L. and F.C. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by research awards from the Fraxa research foundation.

Institutional Review Board Statement

This study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Centre de Recherche du Centre Hospitalier de l’Université de Sherbrooke (2020-3552) and the IRB of Raul Carrea Institute for neurological science (FLENI) (2016, FXS-001).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Not applicable.

Acknowledgments

We thank all the Fragile X Syndrome participants and their caregivers as well as all the healthy controls for their participation in this study. We appreciate the nurses for their support during the recruitment. We acknowledge the L’Association X Fragile Québec (Hospital center of the University of Sherbrooke), Síndrome X Frágil Argentina Association, and the IEB institute (university of Chile). Special thanks to the FRAXA research foundation for all the support they provided to this project. In the end, we thank Horacio Martinetto for the support he provided to this project.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Hernandez, R.N.; Feinberg, R.L.; Vaurio, R.; Passanante, N.M.; Thompson, R.E.; Kaufmann, W.E. Autism Spectrum Disorder in Fragile X Syndrome: A Longitudinal Evaluation. Am. J. Med. Genet A 2009, 149A, 1125–1137. [Google Scholar] [CrossRef] [PubMed]
  2. Roberts, J.E.; McCary, L.M.; Shinkareva, S.V.; Bailey, D.B. Infant Development in Fragile X Syndrome: Cross-Syndrome Comparisons. J. Autism Dev. Disord. 2016, 46, 2088–2099. [Google Scholar] [CrossRef] [PubMed]
  3. Berry-Kravis, E.M.; Lindemann, L.; Jønch, A.E.; Apostol, G.; Bear, M.F.; Carpenter, R.L.; Crawley, J.N.; Curie, A.; Des Portes, V.; Hossain, F.; et al. Drug Development for Neurodevelopmental Disorders: Lessons Learned from Fragile X Syndrome. Nat. Rev. Drug Discov. 2018, 17, 280–298. [Google Scholar] [CrossRef] [PubMed]
  4. Lightbody, A.A.; Reiss, A.L. Gene, Brain, and Behavior Relationships in Fragile X Syndrome: Evidence from Neuroimaging Studies. Dev. Disabil. Res. Rev. 2009, 15, 343–352. [Google Scholar] [CrossRef]
  5. Verhelj, C.; de Graaff, E.; Bakker, C.E.; Willemsen, R.; Willems, P.J.; Meijer, N.; Galjaard, H.; Reuser, A.J.J.; Oostra, B.A.; Hoogeveen, A.T. Characterization of FMR1 Proteins Isolated from Different Tissues. Hum. Mol. Genet. 1995, 4, 895–901. [Google Scholar] [CrossRef]
  6. Berry-Kravis, E.M.; Levin, R.; Shah, H.; Mathur, S.; Darnell, J.C.; Ouyang, B. Cholesterol Levels in Fragile X Syndrome. Am. J. Med. Genet A 2015, 167A, 379–384. [Google Scholar] [CrossRef]
  7. Çaku, A.; Seidah, N.G.; Lortie, A.; Gagné, N.; Perron, P.; Dubé, J.; Corbin, F. New Insights of Altered Lipid Profile in Fragile X Syndrome. PLoS ONE 2017, 12, e0174301. [Google Scholar] [CrossRef]
  8. Lisik, M.Z.; Gutmajster, E.; Sieroń, A.L. Low Levels of HDL in Fragile X Syndrome Patients. Lipids 2016, 51, 189–192. [Google Scholar] [CrossRef]
  9. Lumaban, J.G.; Nelson, D.L. The Fragile X Proteins Fmrp and Fxr2p Cooperate to Regulate Glucose Metabolism in Mice. Hum. Mol. Genet. 2015, 24, 2175–2184. [Google Scholar] [CrossRef]
  10. Wainwright, P.E. Dietary Essential Fatty Acids and Brain Function: A Developmental Perspective on Mechanisms. Proc. Nutr. Soc. 2002, 61, 61–69. [Google Scholar] [CrossRef]
  11. Saini, R.K.; Keum, Y.-S. Omega-3 and Omega-6 Polyunsaturated Fatty Acids: Dietary Sources, Metabolism, and Significance—A Review. Life Sci. 2018, 203, 255–267. [Google Scholar] [CrossRef]
  12. Kidd, P.M. Omega-3 DHA and EPA for Cognition, Behavior, and Mood: Clinical Findings and Structural-Functional Synergies with Cell Membrane Phospholipids. Altern. Med. Rev. 2007, 12, 207–227. [Google Scholar]
  13. Plourde, M.; Cunnane, S.C. Extremely Limited Synthesis of Long Chain Polyunsaturates in Adults: Implications for Their Dietary Essentiality and Use as Supplements. Appl. Physiol. Nutr. Metab. 2007, 32, 619–634. [Google Scholar] [CrossRef]
  14. von Schacky, C. Importance of EPA and DHA Blood Levels in Brain Structure and Function. Nutrients 2021, 13, 1074. [Google Scholar] [CrossRef]
  15. Chalon, S. The Role of Fatty Acids in the Treatment of ADHD. Neuropharmacology 2009, 57, 636–639. [Google Scholar] [CrossRef]
  16. Esposito, C.M.; Buoli, M.; Ciappolino, V.; Agostoni, C.; Brambilla, P. The Role of Cholesterol and Fatty Acids in the Etiology and Diagnosis of Autism Spectrum Disorders. Int. J. Mol. Sci. 2021, 22, 3550. [Google Scholar] [CrossRef]
  17. Kao, Y.-C.; Ho, P.-C.; Tu, Y.-K.; Jou, I.-M.; Tsai, K.-J. Lipids and Alzheimer’s Disease. Int. J. Mol. Sci. 2020, 21, 1505. [Google Scholar] [CrossRef]
  18. Puri, B.K.; Gazizova, D. Chapter 28-Omega-3 Fatty Acids in Intellectual Disability, Schizophrenia, Depression, Autism, and Attention-Deficit Hyperactivity Disorder. In Omega-3 Fatty Acids in Brain and Neurological Health; Watson, R.R., De Meester, F., Eds.; Academic Press: Boston, MA, USA, 2014; pp. 349–358. ISBN 978-0-12-410527-0. [Google Scholar]
  19. Tsaluchidu, S.; Cocchi, M.; Tonello, L.; Puri, B.K. Fatty Acids and Oxidative Stress in Psychiatric Disorders. BMC Psychiatry 2008, 8, S5. [Google Scholar] [CrossRef]
  20. Jory, J. Abnormal Fatty Acids in Canadian Children with Autism. Nutrition 2016, 32, 474–477. [Google Scholar] [CrossRef]
  21. Mostafa, G.A.; AL-Ayadhi, L.Y. Reduced Levels of Plasma Polyunsaturated Fatty Acids and Serum Carnitine in Autistic Children: Relation to Gastrointestinal Manifestations. Behav. Brain Funct. 2015, 11, 4. [Google Scholar] [CrossRef]
  22. Amminger, G.P.; Berger, G.E.; Schäfer, M.R.; Klier, C.; Friedrich, M.H.; Feucht, M. Omega-3 Fatty Acids Supplementation in Children with Autism: A Double-Blind Randomized, Placebo-Controlled Pilot Study. Biol. Psychiatry 2007, 61, 551–553. [Google Scholar] [CrossRef]
  23. Keim, S.A.; Gracious, B.; Boone, K.M.; Klebanoff, M.A.; Rogers, L.K.; Rausch, J.; Coury, D.L.; Sheppard, K.W.; Husk, J.; Rhoda, D.A. ω-3 and ω-6 Fatty Acid Supplementation May Reduce Autism Symptoms Based on Parent Report in Preterm Toddlers. J. Nutr. 2018, 148, 227–235. [Google Scholar] [CrossRef]
  24. Meguid, N.A.; Atta, H.M.; Gouda, A.S.; Khalil, R.O. Role of Polyunsaturated Fatty Acids in the Management of Egyptian Children with Autism. Clin. Biochem. 2008, 41, 1044–1048. [Google Scholar] [CrossRef]
  25. Johnston, M.R.; Sobhi, H.F. Advances in Fatty Acid Analysis for Clinical Investigation and Diagnosis Using GC/MS Methodology. J. Biochem. Anal. Stud. 2017, 3, 1–11. [Google Scholar] [CrossRef]
  26. Krafft, C.; Neudert, L.; Simat, T.; Salzer, R. Near Infrared Raman Spectra of Human Brain Lipids. Spectrochim. Acta Part A Mol. Biomol. 2005, 61, 1529–1535. [Google Scholar] [CrossRef]
  27. De Carvalho, C.C.C.R.; Caramujo, M.J. The Various Roles of Fatty Acids. Molecules 2018, 23, 2583. [Google Scholar] [CrossRef]
  28. Hussain, G.; Wang, J.; Rasul, A.; Anwar, H.; Imran, A.; Qasim, M.; Zafar, S.; Kamran, S.K.S.; Razzaq, A.; Aziz, N.; et al. Role of Cholesterol and Sphingolipids in Brain Development and Neurological Diseases. Lipids Health Dis. 2019, 18, 26. [Google Scholar] [CrossRef]
  29. Toupin, A.; Benachenhou, S.; Abolghasemi, A.; Laroui, A.; Galarneau, L.; Fülöp, T.; Corbin, F.; Çaku, A. Association of Lipid Rafts Cholesterol with Clinical Profile in Fragile X Syndrome. Sci. Rep. 2022, 12, 2936. [Google Scholar] [CrossRef]
  30. Egawa, J.; Pearn, M.L.; Lemkuil, B.P.; Patel, P.M.; Head, B.P. Membrane Lipid Rafts and Neurobiology: Age-Related Changes in Membrane Lipids and Loss of Neuronal Function. J. Physiol. 2016, 594, 4565–4579. [Google Scholar] [CrossRef]
  31. Wiest, M.M.; German, J.B.; Harvey, D.J.; Watkins, S.M.; Hertz-Picciotto, I. Plasma Fatty Acid Profiles in Autism: A Case-Control Study. Prostaglandins Leukot. Essent. Fat. Acids 2009, 80, 221–227. [Google Scholar] [CrossRef]
  32. Vancassel, S.; Durand, G.; Barthélémy, C.; Lejeune, B.; Martineau, J.; Guilloteau, D.; Andrès, C.; Chalon, S. Plasma Fatty Acid Levels in Autistic Children. Prostaglandins Leukot. Essent. Fat. Acids 2001, 65, 1–7. [Google Scholar] [CrossRef] [PubMed]
  33. Colter, A.L.; Cutler, C.; Meckling, K.A. Fatty Acid Status and Behavioural Symptoms of Attention Deficit Hyperactivity Disorder in Adolescents: A Case-Control Study. Nutr. J. 2008, 7, 8. [Google Scholar] [CrossRef] [PubMed]
  34. Abbeduto, L.; McDuffie, A.; Thurman, A.J. The Fragile X Syndrome–Autism Comorbidity: What Do We Really Know? Front. Genet. 2014, 5, 355. [Google Scholar] [CrossRef] [PubMed]
  35. Sullivan, K.; Hatton, D.; Hammer, J.; Sideris, J.; Hooper, S.; Ornstein, P.; Bailey, D., Jr. ADHD Symptoms in Children with FXS. Am. J. Med. Genet. Part A 2006, 140A, 2275–2288. [Google Scholar] [CrossRef]
  36. Pietropaolo, S.; Goubran, M.; Joffre, C.; Aubert, A.; Lemaire-Mayo, V.; Crusio, W.E.; Layé, S. Dietary Supplementation of Omega-3 Fatty Acids Rescues Fragile X Phenotypes in Fmr1-Ko Mice. Psychoneuroendocrinology 2014, 49, 119–129. [Google Scholar] [CrossRef]
  37. Schiavi, S.; Carbone, E.; Melancia, F.; Buzzelli, V.; Manduca, A.; Campolongo, P.; Pallottini, V.; Trezza, V. Perinatal Supplementation with Omega-3 Fatty Acids Corrects the Aberrant Social and Cognitive Traits Observed in a Genetic Model of Autism Based on FMR1 Deletion in Rats. Nutr. Neurosci. 2022, 25, 898–911. [Google Scholar] [CrossRef]
  38. Politi, P.; Cena, H.; Comelli, M.; Marrone, G.; Allegri, C.; Emanuele, E.; Ucelli di Nemi, S. Behavioral Effects of Omega-3 Fatty Acid Supplementation in Young Adults with Severe Autism: An Open Label Study. Arch. Med. Res. 2008, 39, 682–685. [Google Scholar] [CrossRef]
  39. Patrick, L.; Salik, R. Benefits of Essential Fatty Acid Supplementation on Language and Learning Skills in Autism and Asperger’s Syndrome. Autism Asperger’s Dig. 2005, 36–37. [Google Scholar]
  40. Meiri, G.; Bichovsky, Y.; Belmaker, R.H. Omega 3 Fatty Acid Treatment in Autism. J. Child Adolesc. Psychopharmacol. 2009, 19, 449–451. [Google Scholar] [CrossRef]
  41. de la Torre-Aguilar, M.J.; Gomez-Fernandez, A.; Flores-Rojas, K.; Martin-Borreguero, P.; Mesa, M.D.; Perez-Navero, J.L.; Olivares, M.; Gil, A.; Gil-Campos, M. Docosahexaenoic and Eicosapentaenoic Intervention Modifies Plasma and Erythrocyte Omega-3 Fatty Acid Profiles but not the Clinical Course of Children with Autism Spectrum Disorder: A Randomized Control Trial. Front. Nutr. 2022, 9, 790250. [Google Scholar] [CrossRef]
  42. Bos, D.J.; Oranje, B.; Veerhoek, E.S.; Van Diepen, R.M.; Weusten, J.M.; Demmelmair, H.; Koletzko, B.; de Sain-van der Velden, M.G.; Eilander, A.; Hoeksma, M.; et al. Reduced Symptoms of Inattention after Dietary Omega-3 Fatty Acid Supplementation in Boys with and without Attention Deficit/Hyperactivity Disorder. Neuropsychopharmacology 2015, 40, 2298–2306. [Google Scholar] [CrossRef]
  43. Widenhorn-Müller, K.; Schwanda, S.; Scholz, E.; Spitzer, M.; Bode, H. Effect of Supplementation with Long-Chain ω-3 Polyunsaturated Fatty Acids on Behavior and Cognition in Children with Attention Deficit/Hyperactivity Disorder (ADHD): A Randomized Placebo-Controlled Intervention Trial. Prostaglandins Leukot. Essent. Fat. Acids 2014, 91, 49–60. [Google Scholar] [CrossRef]
  44. Murru, E.; Banni, S.; Carta, G. Nutritional Properties of Dietary Omega-3-Enriched Phospholipids. BioMed Res. Int. 2013, 2013, 965417. [Google Scholar] [CrossRef]
  45. Mallick, R.; Basak, S.; Duttaroy, A.K. Docosahexaenoic Acid, 22:6n-3: Its Roles in the Structure and Function of the Brain. Int. J. Dev. Neurosci. 2019, 79, 21–31. [Google Scholar] [CrossRef]
  46. Serhan, C.N.; Petasis, N.A. Resolvins and Protectins in Inflammation Resolution. Chem. Rev. 2011, 111, 5922–5943. [Google Scholar] [CrossRef]
  47. Metherel, A.H.; Irfan, M.; Klingel, S.L.; Mutch, D.M.; Bazinet, R.P. Compound-Specific Isotope Analysis Reveals No Retroconversion of DHA to EPA but Substantial Conversion of EPA to DHA Following Supplementation: A Randomized Control Trial. Am. J. Clin. Nutr. 2019, 110, 823–831. [Google Scholar] [CrossRef]
  48. El-Ansary, A.K.; Ben Bacha, A.G.; Al- Ayahdi, L.Y. Plasma Fatty Acids as Diagnostic Markers in Autistic Patients from Saudi Arabia. Lipids Health Dis. 2011, 10, 62. [Google Scholar] [CrossRef]
  49. Davidson, E.A.; Pickens, C.A.; Fenton, J.I. Increasing Dietary EPA and DHA Influence Estimated Fatty Acid Desaturase Activity in Systemic Organs Which Is Reflected in the Red Blood Cell in Mice. Int. J. Food Sci. Nutr. 2018, 69, 183–191. [Google Scholar] [CrossRef]
  50. El Boustani, S.; Causse, J.E.; Descomps, B.; Monnier, L.; Mendy, F.; de Paulet, A. Direct in Vivo Characterization of Delta 5 Desaturase Activity in Humans by Deuterium Labeling: Effect of Insulin. Metab.-Clin. Exp. 1989, 38, 315–321. [Google Scholar] [CrossRef]
  51. Horrobin, D.F. Fatty Acid Metabolism in Health and Disease: The Role of Δ-6-Desaturase. Am. J. Clin. Nutr. 1993, 57, 732S–737S. [Google Scholar] [CrossRef]
  52. Brenner, R.R.; Peluffo, R.O. Effect of Saturated and Unsaturated Fatty Acids on the Desaturation in Vitro of Palmitic, Stearic, Oleic, Linoleic, and Linolenic Acids. J. Biol. Chem. 1966, 241, 5213–5219. [Google Scholar] [CrossRef]
  53. Czumaj, A.; Śledziński, T. Biological Role of Unsaturated Fatty Acid Desaturases in Health and Disease. Nutrients 2020, 12, 356. [Google Scholar] [CrossRef] [Green Version]
  54. Hagfors, L.; Nilsson, I.; Sköldstam, L.; Johansson, G. Fat Intake and Composition of Fatty Acids in Serum Phospholipids in a Randomized, Controlled, Mediterranean Dietary Intervention Study on Patients with Rheumatoid Arthritis. Nutr. Metab. 2005, 2, 26. [Google Scholar] [CrossRef]
  55. Kohlmeier, L. Future of Dietary Exposure Assessment. Am. J. Clin. Nutr. 1995, 61, 702S–709S. [Google Scholar] [CrossRef]
  56. Kohlmeier, L. Biomarkers of Fatty Acid Exposure and Breast Cancer Risk. Am. J. Clin. Nutr. 1997, 66, 1548S–1556S. [Google Scholar] [CrossRef]
  57. Folch, J.; Lees, M.; Stanley, G.H.S. A Simple Method for the Isolation and Purification of Total Lipides from Animal Tissues. J. Biol. Chem. 1957, 226, 497–509. [Google Scholar] [CrossRef]
  58. Chouinard-Watkins, R.; Conway, V.; Minihane, A.M.; Jackson, K.G.; Lovegrove, J.A.; Plourde, M. Interaction between BMI and APOE Genotype Is Associated with Changes in the Plasma Long-Chain–PUFA Response to a Fish-Oil Supplement in Healthy Participants. Am. J. Clin. Nutr. 2015, 102, 505–513. [Google Scholar] [CrossRef]
  59. Chevalier, L.; Vachon, A.; Plourde, M. Pharmacokinetics of Supplemental Omega-3 Fatty Acids Esterified in Monoglycerides, Ethyl Esters, or Triglycerides in Adults in a Randomized Crossover Trial. J. Nutr. 2021, 151, 1111–1118. [Google Scholar] [CrossRef]
  60. Benjamini, Y.; Hochberg, Y. Controlling the False Discovery Rate: A Practical and Powerful Approach to Multiple Testing. J. R. Stat. Society. Ser. B 1995, 57, 289–300. [Google Scholar] [CrossRef]
Figure 1. Concentrations of selected ω-6 FAs in plasma. Levels are expressed in mg/L of plasma. * p ≤ 0.05; ** p ≤ 0.01. Δ6, delta6-desaturase; Δ5, delta5-desaturase.
Figure 1. Concentrations of selected ω-6 FAs in plasma. Levels are expressed in mg/L of plasma. * p ≤ 0.05; ** p ≤ 0.01. Δ6, delta6-desaturase; Δ5, delta5-desaturase.
Ijms 23 10815 g001
Figure 2. Concentrations of selected ω-3 FAs in plasma. Levels are expressed as mg/L of plasma. * p ≤ 0.05; ** p ≤ 0.01, Δ6, delta6-desaturase; Δ5, delta5-desaturase.
Figure 2. Concentrations of selected ω-3 FAs in plasma. Levels are expressed as mg/L of plasma. * p ≤ 0.05; ** p ≤ 0.01, Δ6, delta6-desaturase; Δ5, delta5-desaturase.
Ijms 23 10815 g002
Table 1. Characteristics of Participants.
Table 1. Characteristics of Participants.
FXSControlsp-Value
All cohorts (N)3434NA
  Argentinians (N)2323
  French-Canadians (N)1111
Sex N (% males)28 (91%)28 (91%)>0.99 1
Age (mean ± SD)22.8 ± 12.823.7 ± 13.60.77 2
  Children, N (mean yrs ± SD)9 (6.3 ± 0.9)9 (6.0 ± 1.2)0.51
  Adolescents N (mean yrs ± SD)4 (14.8 ± 3.8)4 (14.8 ± 3.8)>0.99
  Adults, N (mean yrs ± SD)21 (31.6 ± 7.6)21 (33.1 ± 7.1)0.52
FXS diagnosis
  Full mutation (%)88.6
  Mosaic (%)11.4
1 Fisher test. 2 t-test.
Table 2. FAs Profile in Plasma.
Table 2. FAs Profile in Plasma.
Fatty AcidsFXS (n = 34)
Median in mg/L
[IQ1, IQ3]
Controls (n = 34)
Median in mg/L
[IQ1, IQ3]
Adjusted p-Value *
C14:08.3 [6.8, 9.2]9.5 [7.4, 11.0]0.0455
C16:0490.8 [444.4, 530.5]587.5 [534.2, 681.9]0.0008
C18:0362.7 [307.4, 409.2]387.9 [336.4, 460.0]0.1174
SFA total855.1 [737.7, 962.4]978.6 [898.4, 1070.0]0.0017
C16:1 ω-76.6 [5.6, 8.4]10.0 [8.3, 13.4]0.0008
C18:1 ω-9208.3 [181.9, 242.6]242.3 [216.2, 256.0]0.0158
C18:1 ω-720.7 [16.7, 26.1]26.5 [20.3, 30.5]0.0084
MUFA total236.0 [202.0, 276.7]274.4 [254.0, 297.7]0.0084
C18:2 ω-6372.3 [307.6, 436.7]456.5 [389.3, 515.7]0.0008
C20:3 ω-655.3 [38.9, 76.7]66.5 [55.3, 83.9]0.0460
C20:4 ω-6184.6 [161.2, 226.7]212 [173.6, 283.9]0.0489
ω-6 total621.8 [524.5, 717.0]746.5 [655.2, 867.2]0.0013
C18:3 ω-32.8 [2.1, 3.8]3.4 [2.4, 4.2]0.1844
C20:5 ω-36.4 [4.3, 10.2]12.4 [6.9, 15.5]0.0084
C22:5 ω-315.5 [11.5, 19,5]17.1 [15.2, 21,8]0.1844
C22:6 ω-343.8 [34.2, 55.1]60.0 [38.0, 79.9]0.0336
ω-3 total72.1 [57.0, 85.0]93.7 [68.8, 122.5]0.0173
PUFA total684.1 [600.0, 803.3]842.4 [734.9, 962.3]0.0015
ω-3/ω-60.1 [0.1, 0.1]0.1 [0.1, 0.1]0.4400
C20:5/C18:3(EPA/ALA)2.4 [1.6, 3.6]3.1 [2.6, 4.1]0.0410
C22:5/C20:5(DPA/EPA)2.5 [1.4, 3.2]1.6 [1.2, 2.2]0.0455
C22:6/C22:5(DHA/DPA)2.8 [2.3, 3.3]3.5 [2.4, 4.3]0.1844
C22:6/C20:5(DHA/EPA)6.6 [3.9, 10.0]5.3 [2.7, 8.0]0.2148
20:3/18:20.2 [0.1, 0.2]0.2 [0.1, 0.2]0.7947
20:4/20:33.7 [2.6, 4.5]3.3 [2.7, 3.9]0.6797
IQ1: interquartile range; DPA: decosapentonic acid. * Mann–Whitney test adjusted via the FDR test.
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Abolghasemi, A.; Carullo, M.P.; Aguilera, E.C.; Laroui, A.; Plantefeve, R.; Rojas, D.; Benachenhou, S.; Ramírez, M.V.; Proteau-Lemieux, M.; Lepage, J.-F.; et al. Alteration of Fatty Acid Profile in Fragile X Syndrome. Int. J. Mol. Sci. 2022, 23, 10815. https://doi.org/10.3390/ijms231810815

AMA Style

Abolghasemi A, Carullo MP, Aguilera EC, Laroui A, Plantefeve R, Rojas D, Benachenhou S, Ramírez MV, Proteau-Lemieux M, Lepage J-F, et al. Alteration of Fatty Acid Profile in Fragile X Syndrome. International Journal of Molecular Sciences. 2022; 23(18):10815. https://doi.org/10.3390/ijms231810815

Chicago/Turabian Style

Abolghasemi, Armita, Maria Paulina Carullo, Ester Cisneros Aguilera, Asma Laroui, Rosalie Plantefeve, Daniela Rojas, Serine Benachenhou, María Victoria Ramírez, Mélodie Proteau-Lemieux, Jean-François Lepage, and et al. 2022. "Alteration of Fatty Acid Profile in Fragile X Syndrome" International Journal of Molecular Sciences 23, no. 18: 10815. https://doi.org/10.3390/ijms231810815

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