What are longitudinal monozygotic twin studies? For what purpose are they utilized in research and clinical psychology?

each response MUST be 150 words per question
No Plagiarism, must use citations and references
Psychologists and psychiatrists can determine whether an individual is more susceptible to mental illness by conducting a family medical history. Familial pattern and prevalence data for psychological disorders can be found in the DSM 5.

For example if you look under panic disorder in the DSM 5:

“First-degree biological relatives of individuals with panic disorder are up to 8 times more likely to develop panic disorder. If the age at onset of the panic disorder is before 20, first-degree relatives have been found to be up to 20 times more likely to have panic disorder….Twin studies indicate a genetic contribution to the development of panic disorder.”

The DSM 5 has familial information for all the psychological disorders listed in the manual.
Explain

What are longitudinal monozygotic twin studies? For what purpose are they utilized in research and clinical psychology?