3.2 | Analysis of hair metabolome profiles in DCDA-C and DCDA-D twins
Uniform Manifold Approximation and Projection (UMAP) of our hair samples demonstrated distinct global metabolomic separation of DCDA-C, DCDA-D-S, and DCDA-D-L twins (Figure 2A ). DCDA-D-S and DCDA-D-L co-twins more resembled each other, while DCDA-C twins were separated from the larger and smaller DCDA-D twins. In total, nine significant metabolites discriminated DCDA-D-L twins from DCDA-C twins by logistic regression with a p-value less than 0.05 (Figure 2B, comparison 1). This included lower levels of 10,13-dimethyltetradecanoic acid, nicotinamide, three amino acids, and two organic compounds. 17 significant hair metabolites contributed to the separation of the DCDA-D-S and DCDA-C twins (Figure 2B , comparison 2). This encompassed three amino acids and one amino acid derivative at lower levels in DCDA-D-S twins than in DCDA-C twins, while tryptophan, isoleucine, and most of the organic compounds identified in comparison 2 were found at higher levels in DCDA-D-S twins. A single metabolite, cis-aconitic acid, showed higher levels in DCDA-D-L relative to DCDA-D-S (Figure 2B , comparison 3). To find the shared metabolic changes in both larger and smaller DCDA-D co-twins compared to DCDA-C twins, four common differential metabolites in both comparisons 1 and 2 were shortlisted including cysteine, l-leucine, 2-aminobutyric acid, and threonine (Figure 2C ). Noticeably, the lower concentration of cysteine, threonine, and leucine was detected in both DCDA-D-S and DCDA-D-L groups compared to the DCDA-C group. Meanwhile, 2-aminobutyric acid was the only shortlisted metabolite that displayed the lowest concentration in DCDA-C groups compared to both DCDA-D groups.