ERG/5-HTP in Fragile X Syndrome (FXS)

This single-center, Phase 2, single-blind, 4-period sequential study will enroll 15 males Fragile X Syndrome, ages 18-45 years old. The study will begin with a Screening period of up to 28 days. During screening, participants and their parent/legal authorized guardian, if indicated, will review and sign an Informed Consent/Assent form prior to any study procedures being performed. Following confirmation of a prior diagnosis for Fragile X, information will be collected to further assess their eligibility. Participants who meet entry criteria and agree to participate will proceed to a Baseline visit. At the Baseline visit (Period 1/Day 1), cognitive, behavioral, ERP and eye tracking assessments will be performed to assess current functioning. The Baseline visit will be followed by four 4-week single-blind treatment periods. During treatment periods, participants will be placed on a different treatment regimen every 4 weeks (listed below). Throughout all 4 periods, participants will take two identical capsules three times a day. If only taking one study drug, they will take one placebo pill with the drug at each dose, and in period 4, they will take two placebo pills at each dose. * Period 1: Ergoloid mesylates (EM) 1 mg three times per day for 4 weeks * Period 2: Ergoloid mesylates (EM) 1 mg TID and 5-hydroxytryptophan (5-HTP) 100 mg three times per day for 4 weeks * Period 3: 5-hydroxytryptophan (5-HTP) 100 mg three times per day for 4 weeks * Period 4: Placebo three times per day for 4 weeks Participants will return to the clinic at the end of each treatment period at weeks 4, 8, 12, and 16 and cognitive and behavioral evaluations will be repeated at these clinic visits. Safety and tolerability assessments will include adverse event monitoring, vital signs, blood chemistry and hematology, and urinalysis. Additionally, participants will be monitored for adverse events via a telephone call at the end of Week 1 of each Period, and one week following completion of Period 4 or following early discontinuation. Total study participation will last up to 21 weeks.