Renal, Endocrine, and Bone Changes in Response to FTC/TDF in Uninfected Young Men Who Have Sex With Men (YMSM).

This is a prospective observational cohort sub-study of subjects enrolled in the ATN 110
(NCT01772823) or ATN 113 (NCT01769456) study. All subjects will be followed for at least 48
weeks. Subjects who meet specific bone or renal criteria at Week 48 of the ATN 110
(NCT01772823) or ATN 113 (NCT01769456) study will be followed for an additional 48 weeks in
the Extension Phase of ATN 110 (NCT01772823) or ATN 113 (NCT01769456) and ATN 117
(NCT01769469). The maximum duration of participation will be 96 weeks.

There is no therapeutic intervention specific to this sub-study, and there are no extra study
visits required for participation in this sub-study. Questionnaires will be administered and
blood and urine samples for laboratory evaluation of potential emtricitabine (FTC)/tenofovir
(TDF) (Truvada®) toxicities will be obtained for this sub-study at visits that are required
by the ATN 110 (NCT01772823) or ATN 113 (NCT01769456) study. Measurement of bone mineral
density (BMD) and bone mineral content (BMC) by dual-energy X-ray absorptiometry (DXA) scan
are planned as a part of the ATN 110 (NCT01772823) and ATN 113 (NCT01769456) studies, and
results will be utilized for the analysis in this study. This study does not require extra
BMD or BMC measurements.

Inclusion Criteria:

- Has been enrolled in ATN 110 (NCT01772823) or ATN 113 (NCT01769456) , and

- Willing and able to provide written informed consent

Exclusion Criteria:

-Subjects exempted from undergoing DXA scans in ATN 110 (NCT01772823) or ATN 113
(NCT01769456) are not eligible to enroll in ATN 117 (NCT01769469).