PLOD1 and type 2 diabetes mellitus: As shown in Figure 1, patients affected by type 2 diabetes mellitus (T2DM) with testosterone deficiency exhibited more severe gut dysbiosis, characterized by increased abundance of Streptococcus, which positively correlated with insulin, C-peptide (CRP), and the homeostatic model assessment of insulin resistance (HOMA-IR), and negatively with LH levels [17].