Clinical trials

White blood cell (WBC) cystine levels serve as the primary therapeutic target for monitoring cysteamine treatment in cystinosis, with a goal of \<1.9 nmol ½ cystine/mg protein as measured 5-6 hours post-dose when treated with immediate-release formulation, Cystagon® , or 11-12 hours post-dose when treated with delayed-release formulation, Procysbi®, using UCSD granulocyte assay. Although cysteamine dosing in cystinosis has traditionally been individualized based on WBC cystine levels, the FDA-approved Cystagon® prescribing information now includes an approximate recommended maintenance dose of 1.30 g/m²/day. When this dosing strategy is plotted against body weight, it aligns with the dosing regimen of TTI-0102 that was found effective in mitochondrial diseases, demonstrating a linear relationship between dose and weight. The main objective of this study is to demonstrate that administration of a single dose of 60 ± 5 mg/kg/day of TTI-0102 (\~26 mg/kg cysteamine base equivalent) allows maintenance of WBC cystine at \<1.9 nmol ½ cystine/mg protein over 24 hours as determined by UCSD granulocyte assay.

The goal of this clinical trial is to investigate oral TTI-0102 to evaluate its pharmacokinetics, safety, and preliminary efficacy in patients with Leigh syndrome spectrum, in three sequences. First sequence will be placebo-controlled and include 12 adolescents and adults weighing more than 40 kg. Second sequence will be open-label and include 3 adults and 3 children weighing 25-40 kg. Third sequence will also be open-label and will include 3 children weighing 20-25 kg. The main questions clinical trial aims to answer are: * Characterize the relationship between TTI-0102 drug levels by measuring 1. cysteamine pharmacokinetic (PK) parameters 2. pharmacodynamic (PD) efficacy measures * Generate a population PK model and determine dose level for later dosing groups * collect data to inform the design of a subsequent phase 2b/3 study of TTI-0102 in this patient population Participants will be asked to: * Take the study drug twice daily for 12 weeks * Visit the clinic for checkups and testing 7 times in total: once prior to study drug dosing, then 5 times over the 12-week treatment period and one more time a month after the last study drug dose.