Gender Incongruence is a condition where a person experiences discomfort or distress because there's a mismatch between their biological sex and gender identity. It's sometimes known as gender dysphoria.
Gender Incongruence is now classified as a Sexual Health Condition, Gender Dysphoria is not a mental illness, but individuals left without support can develop poor mental health, feel isolated from society, suffer anxiety, depression which can lead to self harm practices and suicidal thoughts.
With support from families, friends and wider social contacts, to be recognised as the gender identity they feel to be, through the use of preferred name and pronouns, and the freedom to express their gender, trans people will find themselves a route to happiness.
This route may include social transition, taking steps to alter their appearance / gender expression, and possibly medical treatments to adjust their body to match their gender identity.