Genes
Epigenetic modifications, particularly DNA methylation and microRNAs (miRNAs), might have the potential to identify AR patients. One recent study has demonstrated changes in DNA methylation in tryptase gamma 1 (TPSG1 ), schlafen (SLFN12 ), and mucin 4 (MUC 4 ), following controlled allergen challenge, and suggested that baseline epigenetic status may act as a potential biomarker for AR symptom severity.84 Another recent study has indicated that nasal epigenome associated with asthma, FeNO and IgE may serve as a sensitive biomarker of asthma, allergy and airway inflammation in children.85 Other studies have reported that subsets of circulating miRNAs are solely expressed in the blood of patients with AR and asthmatics and may therefore be used as non-invasive biomarkers for diagnosis and characterization of these diseases.86,87
Metabolites
Metabolites have also been proposed as biomarkers for AR. A very recent study of serum metabolomics has demonstrated that at least nine metabolites (13(S)-HPODE, bilirubin, leukotriene D4, hypoxanthine, L-stercobilinogen, N-succinyl-L-diaminopimelic acid, chlorophyll b, 15-hydroxyeicosatetraenoic acid, and urate) were significantly altered in the serum of AR patients, and therefore may provide a better understanding of the metabolic pathways involved in the aetiology of AR.88 Additionally, decreased serum lactoferrin level has been reported to be associated with the phenotype ofDermatophagoides pteronyssinus (Der p1 )-sensitive AR, and in combination with serum Der p1 -specific IgE level, may serve as a serologic biomarker for early detection of AR.89