Overview
This Frontiers in Molecular Neuroscience mini-review by Stanton, Malijauskaite, McGourty, and Grabrucker (University of Limerick) proposes that metal dyshomeostasis is a candidate connecting axis between the proteome, transcriptome, epigenome, metabolome, microbiome, inflammasome, and lipidome in autism spectrum disorders (ASD). The authors argue that metallomics studies have historically been conducted in isolation from other omics layers and that integrating trace-metal composition data across those layers may explain ASD pathologies that any single layer cannot. The review covers essential-metal dyshomeostasis (zinc, copper, iron, manganese) and toxic-metal accumulation (lead, cadmium, mercury, aluminum) with attention to the gut-brain axis and maternal-fetal exposure pathways. The review carries a declared funding conflict: the work was supported by the International Zinc Association in collaboration with Zinpro Corp., which markets zinc supplements.
Study design
Narrative mini-review (journal header label: “MINI REVIEW”). No primary samples were collected and no original analytical measurements were performed. The authors searched the peer-reviewed literature on ASD and individual omics domains (proteomics, transcriptomics, epigenomics, metabolomics, microbiomics, inflammasomics, lipidomics) and synthesized findings thematically around zinc, copper, iron, manganese, lead, cadmium, mercury, and aluminum. No PRISMA diagram, formal search strategy, or explicit inclusion and exclusion criteria are described in the paper. The review proposes a conceptual model in which the metallome acts as a shared biological correlate underpinning heterogeneous ASD pathology.
Samples
No primary samples. The paper reviews published studies involving children and adults diagnosed with ASD, neurotypical controls, unaffected siblings, and animal models (Shank3 knockout mice, MeCP2-deficient mice, FMR1 knockout mice). The biological matrices studied in cited primary literature include whole blood, serum, plasma, hair, urine, nail, deciduous tooth, cerebrospinal fluid, and post-mortem brain tissue. The age ranges, cohort sizes, and geographic origins of participants vary across the dozens of primary studies cited; this paper does not pool or harmonize them.
Illustrative scope of cited primary studies: Yasuda et al. (2013) covered n = 1,967 hair samples from individuals with ASD and found a correlation between age and abnormal metal levels. A systematic review cited as Yassa et al. (2020) is described as covering more than 100 papers and 100,000 participants for zinc and copper ratios in ASD.
Methods
This paper performed no laboratory analysis. Where cited primary studies are described, analytical methods mentioned include inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS), and serum lipid profiling for ceruloplasmin (copper) and transferrin (iron). No specific instrument models, digestion protocols, calibration procedures, or QA/QC details are provided in this review for any cited study.
Instrument
Not reported. This is a narrative review; no primary analytical instruments were used.
LOD/LOQ
Not reported. This is a narrative review; primary detection limits were the responsibility of the cited studies and are not synthesized here.
CRM/recovery
Not reported. No primary analyses were conducted.
Results values
This paper presents no original concentration measurements. All quantitative values cited in the text originate in primary studies. The following are the specific quantitative claims made in the review text, with the primary source identified as stated by the authors.
Zinc (Zn) in ASD vs. neurotypical controls
Zinc concentrations in individuals with ASD are reported to be “typically decreased between 15 to 40%” relative to neurotypical individuals, based on multiple cited primary studies including Al-Ayadhi (2011), Blaurock-Busch et al. (2011), and Fido and Al-Saad (2005). A systematic review and meta-analysis by Saghazadeh and Rezaei (2017) is cited as confirming lower zinc levels in ASD across multiple matrices. Yasuda et al. (2016) covered zinc/copper ratios in blood.
Zinc/copper (Zn/Cu) ratio as a biomarker
Faber et al. (2009) are cited for the proposition that the plasma zinc/serum copper ratio is a candidate biomarker for ASD. Russo et al. (2011) are cited for a significant correlation between zinc/copper ratios, high-density lipoproteins, and total cholesterol levels in ASD cohorts.
Mercury (Hg) and lead (Pb) in ASD
Skalny et al. (2017; Biol. Psychiatry 79, 340-368) are cited for a systematic review and meta-analysis finding higher blood and erythrocyte mercury and lead levels, and higher hair mercury, in individuals with ASD compared with controls. Sajdel-Kupiec et al. (2015) are cited for a correlation between blood mercury levels and inflammatory-related neuropeptides in children with ASD. Geier et al. (2010) and Geier and Geier (2007) are cited for blood mercury and blood lead as toxicity biomarkers in ASD.
Hair trace elements across multiple metals
Adams et al. (2007; J. Toxicol. Environ. Health A 70, 1046-1051) are cited for lead, zinc, and copper in hair and baby tooth samples. Lakshmi Priya and Geetha (2011; Biol. Trace Elem. Res. 142, 148-158) are cited for copper, zinc, magnesium, selenium, lead, and mercury in hair and nail of children with ASD. Blaurock-Busch et al. (2011) are cited for heavy metals and trace elements in hair and urine of Arab children with ASD, covering lead, zinc, copper, cadmium, and mercury. No specific numeric values from these primary studies are re-quoted in the review text.
Zinc and gut microbiome
The paper cites Reed et al. (2015) and Koren and Tako (2020) for the claim that approximately 20% of dietary zinc is absorbed via intestinal bacteria and that alterations in gut microbial composition occur in response to zinc availability. The microbiome genera Verrucomicrobia, Firmicutes, and Actinobacteria are cited as responsive to zinc status.
Cadmium (Cd) mechanisms
Yang et al. (2016) are cited for cadmium-induced toxicity in rat primary mid-brain neuroglial cultures via oxidative stress from microglia. Wang et al. (2019) are cited for cadmium exposure impairing adult hippocampal neurogenesis. Chen et al. (2016; 10.1016/j.taap.2016.11.011) are cited for cadmium induction of NLRP3 inflammasome via NF-kB in human endothelial cells. No primary concentrations are stated.
Table content
The only table in the paper (Table 1) lists bioinformatics platforms for multi-omics data integration (mixOmics-DIABLO, MINT, omicade4, OmicsPASS, 3Omics, Ingenuity Pathway Analysis, MoCluster, MMOmics) and their working environments. It contains no heavy metal concentration data.
Regulatory context
No regulatory concentration limits (FDA, EU, Codex, WHO/JECFA) for any heavy metal in any food or biological matrix are cited in this paper. The review is a neuroscience mechanisms paper focused on pathophysiological pathways, not food safety regulation. All reference values mentioned are mechanistic or biomarker thresholds drawn from cited clinical and laboratory studies.
Limitations
The authors acknowledge the following limitations. The vast majority of ASD-related omics studies investigated a single omics domain in isolation; few studies simultaneously measured multiple omics layers in the same individuals, limiting the ability to test multi-omics integration hypotheses in a single cohort. ASD is described as having a “highly variable clinical phenotype” and cohorts differ in age, severity, biosample matrix, analytical method, and geographic origin, making cross-study comparison difficult. Findings across metallomics studies are inconsistent and reflect differences in sample size, population, assessment method, and ASD severity. The review explicitly frames all metal-omics associations as correlational; causality between metal dyshomeostasis and ASD pathology is not established. Most mechanistic data come from mouse knockout models whose translation to human ASD is not guaranteed. The declared funding relationship with the International Zinc Association and Zinpro Corp. is a potential source of bias toward positive framing of zinc supplementation as a therapeutic target, though the authors state the funder had no role in design, analysis, writing, or submission decisions.
Evidence fitness
Mechanism context only. This paper is a narrative mini-review with no primary measurements. It is useful as a secondary source for understanding the cross-omics mechanisms through which zinc deficiency and toxic metal elevation (lead, mercury, cadmium) may propagate through the proteome, transcriptome, epigenome, inflammasome, microbiome, and lipidome in ASD populations. It identifies the most-cited primary literature for quantitative values (Adams 2007, Faber 2009, Skalny 2017, Yasuda 2011, Yasuda 2013, Lakshmi Priya 2011, Blaurock-Busch 2011) and those primary studies are the appropriate citation targets when quantitative metal levels in ASD populations are needed. The paper should not be cited as the source of any specific concentration value. The declared funding conflict from the zinc industry warrants additional scrutiny for any zinc-specific conclusions. No food matrices, food products, or dietary exposure estimates are discussed; the matrices are exclusively biological fluids and tissues from clinical ASD studies.
Related evidence
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