INcreased Sun Exposure Without Pain In Research Participants With EPP or XLP

To investigate the efficacy of MT-7117 on time to onset and severity of first prodromal symptoms (burning, tingling, itching, or stinging) associated with sunlight exposure in adults and adolescents with EPP or XLP.

Inclusion Criteria: 1. Subjects provided written informed consent to participate. For minor subjects, both minor's assent and parental consent will be required. 2. Male and female subjects with a confirmed diagnosis of EPP or XLP based on medical history. 3. Subjects aged 12 years to 75 years, inclusive, at Screening. 4. Subjects are willing and able to travel to the study sites for all scheduled visits. 5. In the Investigator's opinion, subject can understand the nature of the study and any risks involved in participation, and willing to cooperate and comply with the protocol restrictions and requirements (including travel and receiving direct sunlight exposure as much as possible). 6. Female subjects who are non-lactating and have a negative urine pregnancy test at baseline visit prior to receiving the first dose of study drug. 7. Female subjects of childbearing potential and male subjects with partner of child-bearing potential currently using/willing to use 2 effective methods of contraception. Additional screening criteria check may apply for qualification. Exclusion Criteria: 1. History or presence of photodermatoses other than EPP or XLP. 2. Subjects who are unwilling or unable to go outside in sunlight during daylight hours most days (e.g., between 1-hour post-sunrise and 1 hour pre-sunset) during the study. 3. Presence or history of any hepatobiliary disease, including druginduced liver injury at screening, determined as clinically significant by the Investigator after the discussion with the Sponsor Medical Monitor. 4. Subjects with aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) ≥ 2.0 × upper limit of normal (ULN) or total bilirubin \>1.5 × ULN at Screening. 5. History (in the last 2 years) or presence of alcohol abuse, or abuse of illicit drugs in the opinion of the Investigator. 6. History of melanoma. 7. Presence of squamous cell carcinoma, basal cell carcinoma, or other malignant skin lesions. Any suspicious lesions or nevi will be evaluated. If the suspicious lesion or nevi cannot be resolved through biopsy or excision, the subject will be excluded from the study. 8. History or presence of psychiatric disease judged to be clinically significant by the Investigator and which may interfere with the study evaluation and/or safety of the subjects. 9. Presence of clinically significant acute or chronic renal disease or subjects with an estimated glomerular filtration rate (eGFR) \