Inclusion Criteria:  INCLUSION CRITERIA FOR TRANSGENDER BOYS AND TRANSGENDER MEN  Sex assigned female at birth and a male gender identity (i.e., transgender male) Aged 12-30 years Have a care provider in the Children's Wisconsin Gender Health Clinic or Froedtert Hospital Inclusion Clinic who has determined the individual meets clinical criteria to start testosterone therapy and plans to initiate this therapy Naïve to testosterone or other masculinizing medical therapy Cisgender girls/women and transgender boys/men of child-bearing potential (defined as having achieved menarche (first menses), excluding those who have had a hysterectomy or are on GnRH agonist therapy (puberty blockers)) must be willing to use effective birth control (which may include abstinence)) from screening visit until final study visit Willing and able to give informed consent or have parent or legal guardian provide informed consent if the subject is < 18 years of age  INCLUSION CRITERIA FOR CISGENDER INDIVIDUALS  Gender identity concordant with sex assigned at birth (i.e., cisgender) Aged 12-30 years Not related to a transgender participant enrolled in the study Naïve to any sex hormone or pubertal blocker therapy or, specific to cisgender girls/women only, must be ≥ 1 year from use of oral contraceptive or other contraceptive technique (intrauterine device, medroxyprogesterone injections) Willing and able to give informed consent or have parent or legal guardian provide informed consent if the subject is < 18 years of age  INCLUSION CRITERIA FOR OPTIONAL NITROGLYCERIN ENDOTHELIUM-INDEPENDENT VASCULAR FUNCTION STUDY  Aged ≥ 18 years No history of migraine headaches Systolic blood pressure ≥ 110 mm Hg No prior past adverse reaction to nitroglycerin Has not used a PDE5 inhibitor (i.e., sildenafil, tadalafil, vardenafil) in the past 7 days  Exclusion Criteria:  -